2009 swine flu pandemic
2009 swine flu pandemic | |
---|---|
Pigs, likely indirectly | |
Location | Worldwide |
First outbreak | North America[1][2] |
Index case | Veracruz, Mexico[1][3] |
Arrival date | September 2008[4][5] |
Date | January 2009 – 10 August 2010[6][7] |
Confirmed cases | 491,382 (lab-confirmed)[8] |
Suspected cases‡ | 700 million to 1.4 billion (estimate)[9] |
Deaths | Lab confirmed deaths: 18,449 (reported to the WHO)[10] Estimated excess death: 284,000[11] |
‡Suspected cases have not been confirmed by laboratory tests as being due to this strain, although some other strains may have been ruled out. |
Influenza (flu) |
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The 2009 swine flu pandemic, caused by the
Some studies estimated that the real number of cases including asymptomatic and mild cases could be 700 million to 1.4 billion people—or 11 to 21 percent of the global population of 6.8 billion at the time.[9] The lower value of 700 million is more than the 500 million people estimated to have been infected by the Spanish flu pandemic.[18] However, the Spanish flu infected approximately a third of the world population at the time, a much higher proportion.[19]
The number of lab-confirmed deaths reported to the WHO is 18,449[10] and is widely considered a gross underestimate.[20] The WHO collaborated with the US Centers for Disease Control and Prevention (USCDC) and Netherlands Institute for Health Services Research (NIVEL) to produce two independent estimates of the influenza deaths that occurred during the global pandemic using two distinct methodologies. The 2009 H1N1 flu pandemic is estimated to have actually caused about 284,000 (range from 150,000 to 575,000) excess deaths by the WHO-USCDC study and 148,000–249,000 excess respiratory deaths by the WHO-NIVEL study.[21][22] A study done in September 2010 showed that the risk of serious illness resulting from the 2009 H1N1 flu was no higher than that of the yearly seasonal flu.[23] For comparison, the WHO estimates that 250,000 to 500,000 people die of seasonal flu annually.[24] However, the H1N1 influenza epidemic in 2009 resulted in a large increase in the number of new cases of narcolepsy.[25]
Unlike most strains of influenza, the
Name
The World Health Organization uses the term "(H1N1) 2009 pandemic" when referring to the event, and officially adopted the name "A(H1N1)pdm09" for the virus in 2010, after the conclusion of the pandemic.[31]
Controversy arose early on regarding the wide assortment of terms used by journalists, academics, and officials. Labels like "H1N1 flu", "Swine flu", "Mexican flu", and variations thereof were typical. Criticism centered on how these names may confuse or mislead the public. It was argued that the names were
Official entities adopted terms with varying consistency over the course of the pandemic. The
As terminology changed to deal with these and other such issues, further criticism was made that the situation was unnecessarily confusing. For example, the news department at the journal Science produced an article with the humorous title "Swine Flu Names Evolving Faster Than Swine Flu Itself".[39]
History
Analysis of the genetic divergence of the virus in samples from different cases indicated that the virus jumped to humans in 2008, probably after June, and not later than the end of November,[40] likely around September 2008.[4][5] The research also indicated the virus had been latent in pigs for several months prior to the outbreak, suggesting a need to increase agricultural surveillance to prevent future outbreaks.[41] In 2009, U.S. agricultural officials speculated, although emphasizing that there was no way to prove their hypothesis, that "contrary to the popular assumption that the new swine flu pandemic arose on factory farms in Mexico, [the virus] most likely emerged in pigs in Asia, but then traveled to North America in a human."[15] However, a subsequent report[42] by researchers at the Mount Sinai School of Medicine in 2016 found that the 2009 H1N1 virus likely originated from pigs in a very small region of central Mexico.[43]
Initially called an "outbreak", widespread H1N1 infection was first recognized in the state of
Despite being informally called "swine flu", the H1N1 flu virus cannot be spread by eating pork products;
The pandemic began to taper off in November 2009,[51] and by May 2010, the number of cases was in steep decline.[52][53][54][55] On 10 August 2010, the Director-General of the WHO, Margaret Chan, announced the end of the H1N1 pandemic[7] and announced that the H1N1 influenza event had moved into the post-pandemic period.[56] According to WHO statistics (as of July 2010), the virus had killed more than 18,000 people since it appeared in April 2009; however, they state that the total mortality (including deaths unconfirmed or unreported) from the H1N1 strain is "unquestionably higher".[52][57] Critics claimed the WHO had exaggerated the danger, spreading "fear and confusion" rather than "immediate information".[58] The WHO began an investigation to determine[59] whether it had "frightened people unnecessarily".[60] A flu follow-up study done in September 2010, found that "the risk of most serious complications was not elevated in adults or children."[61] In a 5 August 2011 PLOS ONE article, researchers estimated that the 2009 H1N1 global infection rate was 11% to 21%, lower than what was previously expected.[62] However, by 2012, research showed that as many as 579,000 people could have been killed by the disease, as only those fatalities confirmed by laboratory testing were included in the original number, and meant that many without access to health facilities went uncounted. The majority of these deaths occurred in Africa and Southeast Asia. Experts, including the WHO, have agreed that an estimated 284,500 people were killed by the disease, much higher than the initial death toll.[63][64]
Signs and symptoms
The symptoms of H1N1 flu are similar to those of other
In September 2009, the CDC reported that the H1N1 flu "seems to be taking a heavier toll among chronically ill children than the seasonal flu usually does".[30] Through 8 August 2009, the CDC had received 36 reports of pediatric deaths with associated influenza symptoms and laboratory-confirmed pandemic H1N1 from state and local health authorities within the United States, with 22 of these children having neurodevelopmental conditions such as cerebral palsy, muscular dystrophy, or developmental delays.[70] "Children with nerve and muscle problems may be at especially high risk for complications because they cannot cough hard enough to clear their airways".[30] From 26 April 2009, to 13 February 2010, the CDC had received reports of the deaths of 277 children with laboratory-confirmed 2009 influenza A (H1N1) within the United States.[71]
Severe cases
The World Health Organization reports that the clinical picture in severe cases is strikingly different from the disease pattern seen during epidemics of seasonal influenza. While people with certain underlying medical conditions are known to be at increased risk, many severe cases occur in previously healthy people. In severe cases, patients generally begin to deteriorate around three to five days after symptom onset. Deterioration is rapid, with many patients progressing to respiratory failure within 24 hours, requiring immediate admission to an intensive care unit. Upon admission, most patients need immediate respiratory support with mechanical ventilation.[72]
Complications
Most complications have occurred among previously unhealthy individuals, with
A United Kingdom investigation of risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza looked at 631 patients from 55 hospitals admitted with confirmed infection from May through September 2009. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged ≥65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with a severe outcome, as were radiologically confirmed pneumonia and a raised C-reactive protein (CRP) level (≥100 mg/L). 59% of all in-hospital deaths occurred in previously healthy people.[74]
Fulminant (sudden-onset) myocarditis has been linked to infection with H1N1, with at least four cases of myocarditis confirmed in patients also infected with A/H1N1. Three out of the four cases of H1N1-associated myocarditis were classified as fulminant, and one of the patients died.[75] Also, there appears to be a link between severe A/H1N1 influenza infection and pulmonary embolism. In one report, five out of 14 patients admitted to the intensive care unit with severe A/H1N1 infection were found to have pulmonary emboli.[76]
An article published in
Diagnosis
Confirmed diagnosis of pandemic H1N1 flu requires testing of a
On 22 June 2010, the CDC announced a new test called the "CDC Influenza 2009 A (H1N1)pdm Real-Time RT-PCR Panel (IVD)". It uses a molecular biology technique to detect influenza A viruses and specifically the 2009 H1N1 virus. The new test will replace the previous real-time RT-PCR diagnostic test used during the 2009 H1N1 pandemic, which received an emergency use authorization from the U.S. Food and Drug Administration in April 2009. Tests results are available in four hours and are 96% accurate.[84]
Cause
The virus was found to be a novel strain of influenza for which existing
Analyses of the genetic sequences of the first isolates, promptly shared on the
The virus was less lethal than previous pandemic strains and killed about 0.01–0.03% of those infected; the
In June 2010, scientists from Hong Kong reported discovery of a new swine flu virus: a hybrid of the pandemic H1N1 virus and viruses previously found in pigs. It was the first report of a reassortment of the pandemic virus, which in humans had been slow to evolve. Nancy Cox, head of the influenza division at the U.S. Centers for Disease Control and Prevention, has said, "This particular paper is extremely interesting because it demonstrates for the first time what we had worried about at the very onset of the pandemic, and that is that this particular virus, when introduced into pigs, could reassort with the resident viruses in pigs and we would have new gene constellations. And bingo, here we are." Pigs have been termed the mixing vessel of flu because they can be infected both by avian flu viruses, which rarely directly infect people, and by human viruses. When pigs become simultaneously infected with more than one virus, the viruses can swap genes, producing new variants which can pass to humans and sometimes spread amongst them.[93] "Unlike the situation with birds and humans, we have a situation with pigs and humans where there's a two-way street of exchange of viruses. With pigs it's very much a two-way street."[94]
Transmission
Spread of the H1N1 virus is thought to occur in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing by people with influenza. Sometimes people may become infected by touching something—such as a surface or object—with flu viruses on it and then touching their face.[46]
The basic reproduction number (the average number of other individuals whom each infected individual will infect, in a population which has no immunity to the disease) for the 2009 novel H1N1 is estimated to be 1.75.[95] A December 2009 study found that the transmissibility of the H1N1 influenza virus in households is lower than that seen in past pandemics. Most transmissions occur soon before or after the onset of symptoms.[96]
The H1N1 virus has been transmitted to animals, including
Prevention
Because the H1N1 vaccine was initially in short supply in the U.S., the CDC recommended that initial doses should go to priority groups such as pregnant women, people who live with or care for babies under six months old, children six months to four years old and health-care workers.[101] In the UK, the NHS recommended vaccine priority go to people over six months old who were clinically at risk for seasonal flu, pregnant women and households of people with compromised immunity.[102]
Although it was initially thought that two injections would be required, clinical trials showed that the new vaccine protected adults "with only one dose instead of two;" thus the limited vaccine supplies would go twice as far as had been predicted.[103][104] Health officials worldwide were also concerned because the virus was new and could easily mutate and become more virulent, even though most flu symptoms were mild and lasted only a few days without treatment. Officials also urged communities, businesses, and individuals to make contingency plans for possible school closures, multiple employee absences for illness, surges of patients in hospitals, and other effects of potentially widespread outbreaks.[105] Disaster response organizations such as Direct Relief helped by providing protective items to clinical workers to help them stay healthy throughout flu season.[106][107]
In February 2010, the CDC's Advisory Committee on Immunization Practices voted for "universal" flu vaccination in the U.S. to include all people over six months of age. The 2010–2011 vaccine will protect against the 2009 H1N1 pandemic virus and two other flu viruses.[108]
Public health response
On 27 April 2009, the European Union health commissioner advised Europeans to postpone nonessential travel to the United States or Mexico. This followed the discovery of the first confirmed case in Spain.[109] On 6 May 2009, the Public Health Agency of Canada announced that their National Microbiology Laboratory (NML) had mapped the genetic code of the swine flu virus, the first time that had been done.[110] In the U.K., the National Health Service launched a website, the National Pandemic Flu Service,[111] allowing patients to self-assess and get an authorisation number for antiviral medication. The system was expected to reduce the burden on general practitioners.[102]
U.S. officials observed that six years of concern about
Vaccines
By 19 November 2009, doses of vaccine had been administered in over 16 countries. A 2009 review by the U.S. National Institutes of Health (NIH) concluded that the 2009 H1N1 vaccine has a safety profile similar to that of the seasonal vaccine.
In 2011, a study from the US Flu Vaccine Effectiveness Network estimated the overall effectiveness of all pandemic H1N1 vaccines at 56%. A CDC study released 28 January 2013, estimated that the Pandemic H1N1 vaccine saved roughly 300 lives and prevented about a million illnesses in the US. The study concluded that had the vaccination program started two weeks earlier, close to 60% more cases could have been prevented. The study was based on an effectiveness in preventing cases, hospitalizations, and deaths of 62% for all subgroups except people over 65, for whom the effectiveness was estimated at 43%. The effectiveness was based on European and Asian studies and expert opinion. The delay in vaccine administration demonstrated the shortcomings of the world's capacity for vaccine-production, as well as problems with international distribution. Some manufacturers and wealthy countries had concerns regarding liability and regulations, as well as the logistics of transporting, storing, and administering vaccines to be donated to poorer countries.[116]
Accusations of conflict of interest
In January 2010, Wolfgang Wodarg, a German deputy who trained as a physician and chaired the health committee at the Council of Europe, claimed that major firms had organized a "campaign of panic" to put pressure on the World Health Organization (WHO) to declare a "false pandemic" to sell vaccines. Wodarg said the WHO's "false pandemic" flu campaign is "one of the greatest medicine scandals of the century". He said that the "false pandemic" campaign began in May 2009 in Mexico City, when a hundred or so "normal" reported influenza cases were declared to be the beginning of a threatening new pandemic, although he said there was little scientific evidence for it. Nevertheless, he argued that the WHO, "in cooperation with some big pharmaceutical companies and their scientists, re-defined pandemics," removing the statement that "an enormous amount of people have contracted the illness or died" from its existing definition and replacing it by stating simply that there has to be a virus, spreading beyond borders and to which people have no immunity.[117]
The WHO responded by stating that they take their duty to provide independent advice seriously and guarded against interference from outside interests. Announcing a review of the WHO's actions, spokeswoman Fadela Chaib stated: "Criticism is part of an outbreak cycle. We expect and indeed welcome criticism and the chance to discuss it".[118][119] The WHO also stated on their website that "The world is going through a real pandemic. The description of it as a fake is wrong and irresponsible".[120] In March 2010, the Council of Europe launched an enquiry into "the influence of the pharmaceutical companies on the global swine flu campaign", and a preliminary report was in preparation.[121]
On 12 April 2010, Keiji Fukuda, the WHO's top influenza expert, stated that the system leading to the declaration of a pandemic led to confusion about H1N1 circulating around the world and he expressed concern that there was a failure to communicate in regard to uncertainties about the new virus, which turned out to be not as deadly as feared. WHO Director-General Margaret Chan appointed 29 flu experts from outside the organization to conduct a review of WHO's handling of the H1N1 flu pandemic. She told them, "We want a frank, critical, transparent, credible and independent review of our performance."[122]
In June 2010,
Infection control
Travel precautions
On 7 May 2009, the WHO stated that containment was not feasible and that countries should focus on mitigating the effect of the virus. They did not recommend closing borders or restricting travel.
U.S. airlines had made no major changes as of the beginning of June 2009, but continued standing practices which include looking for passengers with symptoms of flu,
According to studies conducted in Australia and Japan, screening individuals for influenza symptoms at airports during the 2009 H1N1 outbreak was not an effective method of infection control.[127][128]
Schools
U.S. government officials were especially concerned about schools because the H1N1 flu virus appeared to disproportionately affect young and school-age people, between six months and 24 years of age.[129] The H1N1 outbreak led to numerous precautionary school closures in some areas. Rather than closing schools, the CDC recommended that students and school workers with flu symptoms should stay home for either seven days total, or until 24 hours after symptoms subsided, whichever was longer.[130] The CDC also recommended that colleges should consider suspending fall 2009 classes if the virus began to cause severe illness in a significantly larger share of students than the previous spring. They also urged schools to suspend rules, such as penalties for late papers or missed classes or requirements for a doctor's note, to enforce "self-isolation" and prevent students from venturing out while ill;[131] schools were advised to set aside a room for people developing flu-like symptoms while they waited to go home and to have ill students or staff and those caring for them use face masks.[132]
In California, school districts and universities were on alert and worked with health officials to launch education campaigns. Many planned to stockpile medical supplies and discuss worst-case scenarios, including plans to provide lessons and meals for low-income children in case elementary and secondary schools closed.[133] University of California campuses stockpiled supplies, from paper masks and hand sanitizer to food and water.[133] To help prepare for contingencies, University of Maryland School of Medicine professor of pediatrics James C. King Jr. suggested that every county should create an "influenza action team" to be run by the local health department, parents, and school administrators.[134] By 28 October 2009, about 600 schools in the United States had been temporarily closed, affecting over 126,000 students in 19 states.[135]
Workplace
Fearing a worst-case scenario, the U.S.
The CDC estimated that as much as 40% of the workforce might be unable to work at the peak of the pandemic due to the need for many healthy adults to stay home and care for an ill family member,[137] and advised that individuals should have steps in place should a workplace close down or a situation arise that requires remote work.[138] The CDC further advised that persons in the workplace should stay home sick for seven days after getting the flu, or 24 hours after symptoms end, whichever is longer.[130]
In the UK, the Health and Safety Executive (HSE) also issued general guidance for employers.[139]
Face masks
The U.S. CDC did not recommend the use of face masks or respirators in non-health care settings, such as schools, workplaces, or public places, with a few exceptions: people who were ill with the virus when around other people, and people who were at risk for severe illness while caring for someone with the flu.[140] There was some disagreement about the value of wearing face masks, as some experts feared that masks may have given people a false sense of security and should not have replaced other standard precautions.[141] Yukihiro Nishiyama, professor of virology at Nagoya University's School of Medicine, commented that the masks are "better than nothing, but it's hard to completely block out an airborne virus since it can easily slip through the gaps".[142][143] According to mask manufacturer
Quarantine
During the height of the fear of a pandemic, some countries initiated or threatened to initiate
Pigs and food safety
The pandemic virus is a type of swine influenza, derived originally from a strain which lived in pigs, and this origin gave rise to the common name of "swine flu". This term is widely used by mass media, though the Paris-based World Organisation for Animal Health as well as industry groups such as the U.S. National Pork Board, the American Meat Institute, and the Canadian Pork Council objected to widespread media use of the name "swine flu" and suggested it should be called "North American flu" instead, while the World Health Organization switched its designation from "swine influenza" to "influenza A (H1N1)" in late April 2009.[153][154] The virus has been found in U.S. hogs,[155] and Canadian[156] as well as in hogs in Northern Ireland, Argentina, and Norway.[157] Leading health agencies and the United States Secretary of Agriculture have stressed that eating properly cooked pork or other food products derived from pigs will not cause flu.[158][159] Nevertheless, on 27 April Azerbaijan imposed a ban on the importation of animal husbandry products from the entire Americas.[160] The Indonesian government also halted the importation of pigs and initiated the examination of 9 million pigs in Indonesia.[161] The Egyptian government ordered the slaughter of all pigs in Egypt on 29 April.[162]
Treatment
A number of methods have been recommended to help ease symptoms, including adequate liquid intake and rest.
If the fever is mild and there are no other complications, fever medication is not recommended.[164] Most people recover without medical attention, although ones with pre-existing or underlying medical conditions are more prone to complications and may benefit from further treatments.[166]
People in at-risk groups should be treated with
To help avoid shortages of these drugs, the U.S. CDC recommended oseltamivir treatment primarily for people hospitalised with pandemic flu; people at risk of serious flu complications due to underlying medical conditions; and patients at risk of serious flu complications. The CDC warned that the indiscriminate use of antiviral medications to prevent and treat influenza could ease the way for
Side effects
Both medications mentioned above for treatment, oseltamivir and zanamivir, have known side effects, including lightheadedness, chills, nausea, vomiting, loss of appetite, and trouble breathing. Children were reported to be at increased risk of self-injury and confusion after taking oseltamivir.[163] The WHO warned against buying antiviral medications from online sources and estimated that half the drugs sold by online pharmacies without a physical address were counterfeit.[171]
Resistance
In December 2012, the
Antivirals effectiveness questioned in healthy adults
On 8 December 2009, the
Epidemiology
Area | Lab confirmed deaths reported to the WHO |
---|---|
Worldwide (total) | At least 18,449 |
Africa | 168 |
Americas | At least 8,533 |
Eastern Mediterranean | 1,019 |
Europe | At least 4,079 |
South-East Asia | 1,992 |
Western Pacific | 1,858 |
Further information: Cases and deaths by country
Note: The ratio of confirmed deaths to total deaths due to the pandemic is unknown. For more information, see "Data reporting and accuracy". |
While it is not known precisely where or when the virus originated,[4][178] analyses in scientific journals have suggested that the H1N1 strain responsible for the 2009 outbreak first evolved in September 2008 and circulated amongst humans for several months, before being formally recognised and identified as a novel strain of influenza.[4][5]
Mexico
The virus was first reported in two U.S. children in March 2009, but health officials have reported that it apparently infected people as early as January 2009 in Mexico.[6] The outbreak was first identified in Mexico City on 18 March 2009;[179] immediately after the outbreak was officially announced, Mexico notified the U.S. and World Health Organization, and within days of the outbreak Mexico City was "effectively shut down".[180] Some countries cancelled flights to Mexico while others halted trade. Calls to close the border to contain the spread were rejected.[180] Mexico already had hundreds of non-lethal cases before the outbreak was officially discovered, and was therefore in the midst of a "silent epidemic". As a result, Mexico was reporting only the most serious cases which showed more severe signs different from those of normal flu, possibly leading to a skewed initial estimate of the case fatality rate.[179]
United States
The new strain was first identified by the CDC in two children, neither of whom had been in contact with pigs. The first case, from
The first confirmed H1N1/09 pandemic flu death, which occurred at Texas Children's Hospital in Houston, Texas, was of a toddler from Mexico City who was visiting family in Brownsville, Texas, before being air-lifted to Houston for treatment.[181] The Infectious Diseases Society of America estimated that the total number of deaths in the U.S. was 12,469.[182]
Data reporting and accuracy
Influenza surveillance information "answers the questions of where, when, and what influenza viruses are circulating. Sharing of such information is especially crucial during an emergent pandemic as in April 2009, when the genetic sequences of the initial viruses were rapidly and openly shared via the GISAID Initiative within days of identification,[183] playing a key role in facilitating an early response to the evolving pandemic.[184][185][186] Surveillance is used to determine if influenza activity is increasing or decreasing, but cannot be used to ascertain how many people have become ill with influenza."[187] For example, as of late June, influenza surveillance information showed the U.S. had nearly 28,000 laboratory-confirmed cases including 3,065 hospitalizations and 127 deaths. But mathematical modelling showed an estimated 1 million Americans had the 2009 pandemic flu at the time, according to Lyn Finelli, a flu surveillance official with the CDC.[188] Estimating deaths from influenza is also a complicated process. In 2005, influenza only appeared on the death certificates of 1,812 people in the US. The average annual US death toll from flu is, however, estimated to be 36,000.[189] The CDC explains:[190] "[I]nfluenza is infrequently listed on death certificates of people who die from flu-related complications" and hence, "Only counting deaths where influenza was included on a death certificate would be a gross underestimation of influenza's true impact."
Influenza surveillance information on the 2009 H1N1 flu pandemic is available, but almost no studies attempted to estimate the total number of deaths attributable to H1N1 flu. Two studies were carried out by the CDC; the later of them estimated that between 7,070 and 13,930 deaths were attributable to H1N1 flu from April to 14 November 2009.[191] During the same period, 1,642 deaths were officially confirmed as caused by H1N1 flu.[192][193] The WHO stated in 2010 that total mortality (including unconfirmed or unreported deaths) from H1N1 flu was "unquestionably higher" than their own confirmed death statistics.[194]
The initial outbreak received a week of near-constant media attention.
Follow-up
A Wisconsin study published in the
CDC illness and death estimates from April 2009 to April 2010, in the US are as follows:
- between 43 million and 89 million cases of 2009 H1N1 occurred between April 2009 and 10 April 2010. The mid-level in this range is about 61 million people infected with 2009 H1N1.
- between about 195,000 and 403,000 H1N1-related hospitalizations occurred between April 2009 and 10 April 2010. The mid-level in this range is about 274,000 2009 H1N1-related hospitalizations.
- between about 8,870 and 18,300 2009 H1N1-related deaths occurred between April 2009 and 10 April 2010. The mid-level in this range is about 12,470 2009 H1N1-related deaths.[199][200][201]
It has been stated that about 36,000 die from the seasonal flu in the U.S. each year,[202] and this is frequently understood as an indication that the H1N1 strain was not as severe as seasonal influenza. The 36,000 estimate was presented in a 2003 study by CDC scientists and refers to a period from 1990 to 1991 through 1998–99. During those years, the number of estimated deaths ranged from 17,000 to 52,000, with an average of about 36,000. Throughout that decade, influenza A (H3N2) was the predominant virus during most of the seasons, and H3N2 influenza viruses are typically associated with higher death rates. The JAMA study also looked at seasonal influenza-associated deaths over a 23-year period, from 1976 to 1977 and 1998–99 with estimates of respiratory and circulatory influenza-associated deaths ranging from about 5,000 to about 52,000, and an average of about 25,000. CDC believes that the range of deaths over the past 31 years (~3,000 to ~49,000) is a more accurate representation of the unpredictability and variability of flu-associated deaths.[203] The annual toll from seasonal influenza in the US between 1979 and 2001 is estimated at 41,400 deaths on average.[204] Therefore, the H1N1 pandemic estimated mortality of 8,870 to 18,300 is just below the mid-range of estimates.[205]
The 2009 pandemic caused US hospitals to make significant preparations in terms of hospital surge capacities, especially within the emergency department and among vulnerable populations. In many cases, hospitals were relatively successful in making sure that those patients most severely affected by the influenza strain were able to be seen, treated, and discharged in an efficient manner. A case-study of the preparation, planning, mitigation, and response efforts during the fall of 2009 is that of the Children's Hospital of Philadelphia (CHOP) which took several steps to increase the emergency department (ED) surge capacity response. CHOP used portions of the main lobby area as an ED waiting room; several of the region's hospital-based outpatient facilities were in use during evening and weekend hours for non-emergency cases; the ED's 24-hour short-stay unit was utilized to care for ED patients in a longer-term capacity; non-board certified physicians (in pediatric emergency medicine) and inpatient-unit medical nurses were utilized for ED patient care; hospital units normally utilized for other medical or therapeutic purposes were transformed into ED patient rooms; and rooms normally used for only one patient were expanded to at least a capacity of 2.[206]
Comparisons to other pandemics and epidemics
Annual influenza epidemics are estimated to affect 5–15% of the global population. Although most cases are mild, these epidemics still cause severe illness in 3–5 million people and 290,000–650,000 deaths worldwide every year.
In addition to these annual epidemics, Influenza A virus strains caused three global pandemics during the 20th century: the Spanish flu in 1918,
The
Name | Date | World pop. | Subtype | Reproduction number[215] | Infected (est.) | Deaths worldwide | Case fatality rate | Pandemic severity |
---|---|---|---|---|---|---|---|---|
Spanish flu[216] | 1918–20 | 1.80 billion | H1N1
|
1.80 (IQR, 1.47–2.27) | 33% (500 million)[217] or >56% (>1 billion)[218] | 17[219]–100[220][221] million | 2–3%,[218] or ~4%, or ~10%[222] | 5 |
Asian flu | 1957–58 | 2.90 billion | H2N2
|
1.65 (IQR, 1.53–1.70) | >17% (>500 million)[218] | 1–4 million[218] | <0.2%[218] | 2 |
Hong Kong flu | 1968–69 | 3.53 billion | H3N2
|
1.80 (IQR, 1.56–1.85) | >14% (>500 million)[218] | 1–4 million[218] | <0.2%[218][223] | 2 |
1977 Russian flu | 1977–79 | 4.21 billion | H1N1
|
? | ? | 0.7 million[224] | ? | ? |
2009 swine flu pandemic[225][226] | 2009–10 | 6.85 billion | H1N1/09 | 1.46 (IQR, 1.30–1.70) | 11–21% (0.7–1.4 billion)[227] | 151,700–575,400[228] | 0.01%[229][230] | 1 |
Typical seasonal flu[t 1] | Every year | 7.75 billion | A/H3N2, A/H1N1, B , ...
|
1.28 (IQR, 1.19–1.37) | 5–15% (340 million – 1 billion)[231] 3–11% or 5–20%[232][233] (240 million – 1.6 billion) |
290,000–650,000/year[234] | <0.1%[235] | 1 |
Notes
|
The influenza virus has caused several pandemic threats over the past century, including the pseudo-pandemic of 1947 (thought of as mild because although globally distributed, it caused relatively few deaths),
People who contracted influenza before 1957 appeared to have some immunity to H1N1 flu. According to Daniel Jernigan, head of flu epidemiology for the U.S. CDC "Tests on blood serum from older people showed that they had antibodies that attacked the new virus ... That does not mean that everyone over 52 is immune, since Americans and Mexicans older than that have died of the new flu".[238]
In June 2012, a model based study found that the number of deaths related to the H1N1 influenza may have been fifteen times higher than the reported laboratory confirmed deaths, with 80% of the respiratory and cardiovascular deaths in people younger than 65 years and 51% occurring in southeast Asia and Africa. A disproportionate number of pandemic deaths might have occurred in these regions and that efforts to prevent future influenza pandemics need to effectively target these regions.[239]
A WHO-supported 2013 study estimated that the 2009 global pandemic respiratory mortality was ~10-fold higher than the World Health Organization's laboratory-confirmed mortality count (18.631). Although the pandemic mortality estimate was similar in magnitude to that of seasonal influenza, a marked shift toward mortality among persons less than 65 years of age occurred, so that many more life-years were lost. Between 123,000 and 203,000 pandemic respiratory deaths were estimated globally for the last nine months of 2009. The majority (62–85%) were attributed to persons under 65 years of age. The burden varied greatly among countries. There was an almost 20-fold higher mortality in some countries in the Americas than in Europe. The model attributed 148,000–249,000 respiratory deaths to influenza in an average pre-pandemic season, with only 19% in persons <65 years of age.[240]
The COVID-19 pandemic is not caused by an influenza virus but SARS-CoV-2, a coronavirus which also primarily affects the respiratory system.
See also
- SARS
- 2009 swine flu pandemic tables
- 2015–16 Zika virus epidemic
- Black Death
- COVID-19 pandemic
- G4 EA H1N1
- Health crisis
- MERS
- Public health emergency (United States)
- Western African Ebola virus epidemic
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Further reading
- Cannell JJ, Zasloff M, Garland CF, Scragg R, Giovannucci E (February 2008). "On the epidemiology of influenza". Virology Journal. 5 (1): 29. PMID 18298852.
- MacPhail T (2014). The Viral Network. Ithaca; London: Cornell University Press. ISBN 978-0-8014-7983-0.
- Smith GJ, Vijaykrishna D, Bahl J, Lycett SJ, Worobey M, Pybus OG, et al. (June 2009). "Origins and evolutionary genomics of the 2009 swine-origin H1N1 influenza A epidemic". Nature. 459 (7250): 1122–25. PMID 19516283.
- Soundararajan V, Tharakaraman K, Raman R, Raguram S, Shriver Z, Sasisekharan V, Sasisekharan R (June 2009). "Extrapolating from sequence – the 2009 H1N1 'swine' influenza virus". Nature Biotechnology. 27 (6): 510–13. S2CID 22710439.
- Centers for Disease Control Prevention (CDC) (October 2009). "Introduction and transmission of 2009 pandemic influenza A (H1N1) Virus – Kenya, June–July 2009". MMWR. Morbidity and Mortality Weekly Report. 58 (41): 1143–46. from the original on 13 May 2011.
External links
- Influenza: H1N1 at Curlie
- Pandemic (H1N1) 2009 at the World Health Organization (WHO)
- International Society for Infectious Diseases PROMED-mail news updates