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	Researchers note that although current vaccines were not designed against the Delta variant, they nonetheless are highly effective, but to a lesser degree: protection fell from 91% to 66%.<ref name=Forbes>[https://www.forbes.com/sites/brucelee/2021/08/24/cdc-covid-19-vaccine-effectiveness-fell-from-91-to-66-with-delta-variant/?sh=27bfdae428f7 "CDC: Covid-19 Vaccine Effectiveness Fell From 91% To 66% With Delta Variant"], ''Forbes'', 24 August 2021</ref>{{Unreliable source?|date=October 2021}}{{Medical citation needed|date=October 2021}} One expert stated that "those who are infected following vaccination are still not getting sick and not dying like was happening before vaccination."<ref name=TNR/> "This virus is the most efficient virus for finding new hosts that are vulnerable," stated Dr. [[Eric Topol]], director and founder of the [[Scripps Research]] Translational Institute.<ref name=TNR/> By late August 2021 the Delta variant accounted for 99 percent of U.S. cases and was found to double the risk of severe illness and hospitalization for those not yet vaccinated.<ref name=LATimes-delta>[https://www.latimes.com/science/story/2021-08-28/hospitalization-risk-doubled-for-unvaccinated-covid-patients-infected-with-delta-variant "Among the unvaccinated, Delta variant more than doubles risk of hospitalization"], ''Los Angeles Times'', 28 August 2021</ref>		Researchers note that although current vaccines were not designed against the Delta variant, they nonetheless are highly effective, but to a lesser degree: protection fell from 91% to 66%.<ref name=Forbes>[https://www.forbes.com/sites/brucelee/2021/08/24/cdc-covid-19-vaccine-effectiveness-fell-from-91-to-66-with-delta-variant/?sh=27bfdae428f7 "CDC: Covid-19 Vaccine Effectiveness Fell From 91% To 66% With Delta Variant"], ''Forbes'', 24 August 2021</ref>{{Unreliable source?|date=October 2021}}{{Medical citation needed|date=October 2021}} One expert stated that "those who are infected following vaccination are still not getting sick and not dying like was happening before vaccination."<ref name=TNR/> "This virus is the most efficient virus for finding new hosts that are vulnerable," stated Dr. [[Eric Topol]], director and founder of the [[Scripps Research]] Translational Institute.<ref name=TNR/> By late August 2021 the Delta variant accounted for 99 percent of U.S. cases and was found to double the risk of severe illness and hospitalization for those not yet vaccinated.<ref name=LATimes-delta>[https://www.latimes.com/science/story/2021-08-28/hospitalization-risk-doubled-for-unvaccinated-covid-patients-infected-with-delta-variant "Among the unvaccinated, Delta variant more than doubles risk of hospitalization"], ''Los Angeles Times'', 28 August 2021</ref>
	In September 2021, the European Journal of Epidemiology published a study demonstrating that increases in COVID-19 are unrelated to levels of vaccination across 68 countries and 2947 counties in the United States. The study also indicated that the trend line suggests a marginally positive association such that countries with a higher percentage of their population fully vaccinated have higher COVID-19 cases per 1 million people. The authors of the study advised that sole reliance on vaccination as a primary strategy to mitigate COVID-19 and its adverse consequences needs to be re-examined, especially considering the Delta variant and the likelihood of future variants.<ref>{{cite journal |title=Increases in COVID-19 are unrelated to levels of vaccination across 68 countries and 2,947 counties in the United States |journal=European Journal of Epidemiology |date=September 30, 2021 |url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8481107/ |access-date=22 October 2021}}</ref>
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Revision as of 01:17, 27 October 2021

Further information: COVID-19 vaccine

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COVID-19 vaccine clinical research is the clinical research on COVID-19 vaccines, including their efficacy, effectiveness and safety. There are 24 vaccines authorized for use by national governments, with six vaccines being approved for emergency or full use by at least one WHO-recognised stringent regulatory authority; and five of them are in Phase IV. 204 vaccines under clinical trials that have not yet been authorized. There are also nine clinical trials on heterologous vaccination courses.

In

Oxford–AstraZeneca, Convidecia, and Janssen), and six subunit vaccines (Abdala, COVAX-19, EpiVacCorona, MVC-COV1901, Soberana 02, and ZF2001).^[1][2] In total, 330 vaccine candidates are in various stages of development, with 102 in clinical research, including 30 in Phase I trials, 30 in Phase I–II trials, 25 in Phase III trials, and 8 in Phase IV development.^[1]

Formulation

This section's factual accuracy may be compromised due to out-of-date information. Please help update this article to reflect recent events or newly available information. (August 2021)

As of September 2020[update], eleven of the vaccine candidates in clinical development use

immunological adjuvant is a substance formulated with a vaccine to elevate the immune response to an antigen, such as the COVID‑19 virus or influenza virus.^[4] Specifically, an adjuvant may be used in formulating a COVID‑19 vaccine candidate to boost its immunogenicity and efficacy to reduce or prevent COVID‑19 infection in vaccinated individuals.^[4][5] Adjuvants used in COVID‑19 vaccine formulation may be particularly effective for technologies using the inactivated COVID‑19 virus and recombinant protein-based or vector-based vaccines. Aluminum salts, known as "alum", were the first adjuvant used for licensed vaccines, and are the adjuvant of choice in some 80% of adjuvanted vaccines.^[5] The alum adjuvant initiates diverse molecular and cellular mechanisms to enhance immunogenicity, including release of proinflammatory cytokines.^[4][5]

Trial and authorization status

Phase I trials test primarily for safety and preliminary dosing in a few dozen healthy subjects, while Phase II trials – following success in Phase I – evaluate

control group, and test effectiveness of the vaccine to prevent the disease (an "interventional" or "pivotal" trial), while monitoring for adverse effects at the optimal dose.^[6][7] Definition of vaccine safety, efficacy, and clinical endpoints in a Phase III trial may vary between the trials of different companies, such as defining the degree of side effects, infection or amount of transmission, and whether the vaccine prevents moderate or severe COVID‑19 infection.^[8][9][10]

A clinical trial design in progress may be modified as an "adaptive design" if accumulating data in the trial provide early insights about positive or negative efficacy of the treatment.^[11][12] Adaptive designs within ongoing Phase II–III clinical trials on candidate vaccines may shorten trial durations and use fewer subjects, possibly expediting decisions for early termination or success, avoiding duplication of research efforts, and enhancing coordination of design changes for the Solidarity trial across its international locations.^[11][13]

List of authorized and approved vaccines

Further information: List of COVID-19 vaccine authorizations

For COVID-19 vaccination policy by country, see Vaccination policy § Table.

National

Biologic License Applications for the Pfizer–BioNTech and Moderna COVID‑19 vaccines have been submitted to the US Food and Drug Administration (FDA).^[14][15]

• 
  RNA vaccines and DNA vaccines

    Pfizer–BioNTech

    Moderna

    ZyCoV-D
• 
  Sputnik V

    Sputnik Light

    Convidecia

Sinopharm (WIBP)

  Others

Medigen (MVC)

  COVAX-19

In July 2021, the U.S. Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) issued a joint statement reporting that a booster dose is not necessary for those who have been fully vaccinated.^[314]

In August 2021, the FDA and the CDC authorized the use of an additional mRNA vaccine dose for immunocompromised individuals.^[315][316] The authorization was extended to cover other specific groups in September 2021.^{[317][318][319]}

In October 2021, the FDA and the CDC authorized the use of either homologous or heterologous vaccine booster doses.^[320][321]

Heterologous prime-boost vaccination

In October 2021, the US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) authorized the use of either homologous or heterologous vaccine booster doses.^[320][321]

Some experts believe that

In February 2021, the Oxford Vaccine Group launched the Com-COV vaccine trial to investigate heterologous prime-boost courses of different COVID-19 vaccines.^[324] As of June 2021, the group is conducting two phase II studies: Com-COV and Com-COV2.^[325]

In Com-COV, the two heterologous combinations of the

In Com-COV2, the first dose is the Oxford–AstraZeneca vaccine or the Pfizer vaccine, and the second dose is the Moderna vaccine, the Novavax vaccine, or a homologous vaccine equal to the first dose, with an interval of 56 or 84 days between doses.^[328]

A study in the UK is evaluating annual heterologous boosters by randomly selecting the following vaccines:

Vaccine efficacy is the reduction in risk of getting the disease by vaccinated participants in a controlled trial compared with the risk of getting the disease by unvaccinated participants.^[338] An efficacy of 0% means that the vaccine does not work (identical to placebo). An efficacy of 50% means that there are half as many cases of infection as in unvaccinated individuals.^{[citation needed]}

COVID-19 vaccine efficacy may be adversely affected if the arm is held improperly or squeezed so the vaccine is

The observed substantial efficacy of certain mRNA vaccines even after partial (1-dose) immunization[349]^[337] indicates a non-linear dose-efficacy relation already seen in the phase I-II study^[350] and suggests that personalization of the vaccine dose (regular dose to the elderly, reduced dose to the healthy young,^[351] additional booster dose to the immunosuppressed^[352]) might allow accelerating vaccination campaigns in settings of limited supplies, thereby shortening the pandemic, as predicted by pandemic modeling.^[353]

Ranges below are 95% confidence intervals unless indicated otherwise, and all values are for all participants regardless of age, according to the references for each of the trials. By definition, the accuracy of the estimates without an associated confidence interval is unknown publicly. Efficacy against severe COVID-19 is the most important, since hospitalizations and deaths are a public health burden whose prevention is a priority.^[354] Authorized and approved vaccines have shown the following efficacies:

Effectiveness

As of August 2021, data from studies in the U.S. and in other countries found that the COVID-19 vaccines available in the United States are "highly protective against severe illness, hospitalization, and death due to COVID-19".^[389] In comparison with fully vaccinated people, the CDC found that unvaccinated people were 5 times more likely to be infected, 10 times more likely to be hospitalized, and 11 times more likely to die.^[390][391]

By late August 2021, after the

As a result of the CDC reports, President Joe Biden said that "virtually all" COVID-19 hospitalizations and deaths in the U.S. were among unvaccinated people.[395] A study in the state of Washington found that unvaccinated people were six times more likely to test positive for COVID-19, 37 times more likely to be hospitalized, and 67 times more likely to die, compared to those who had been vaccinated.^[396]

Researchers note that although current vaccines were not designed against the Delta variant, they nonetheless are highly effective, but to a lesser degree: protection fell from 91% to 66%.^{[397][unreliable source?][medical citation needed]} One expert stated that "those who are infected following vaccination are still not getting sick and not dying like was happening before vaccination."^[393] "This virus is the most efficient virus for finding new hosts that are vulnerable," stated Dr. Eric Topol, director and founder of the Scripps Research Translational Institute.^[393] By late August 2021 the Delta variant accounted for 99 percent of U.S. cases and was found to double the risk of severe illness and hospitalization for those not yet vaccinated.^[398]

Studies

The real-world studies of vaccine effectiveness measure to which extent a certain vaccine has succeeded in preventing COVID-19 infection, symptoms, hospitalization and death for the vaccinated individuals in a large population under routine conditions that are less than ideal.^[399]

• In Israel, among the 715,425 individuals vaccinated by the Moderna or Pfizer-BioNTech vaccines during the period 20 December 2020, to 28 January 2021, it was observed for the period starting seven days after the second shot, that only 317 people (0.04%) became sick with mild/moderate COVID-19 symptoms and only 16 people (0.002%) were hospitalized.^[400]
• The Pfizer-BioNTech and Moderna COVID-19 vaccines provide highly effective protection, according to a report from the U.S. Centers for Disease Control and Prevention (CDC). Under real-world conditions, mRNA vaccine effectiveness of full immunization (≥14 days after second dose) was 90% against SARS-CoV-2 infections regardless of symptom status; vaccine effectiveness of partial immunization (≥14 days after first dose but before second dose) was 80%.^[401]
• 15,121 health care workers from 104 hospitals in England, that all had tested negative for COVID-19 antibodies prior of the study, were followed by RT-PCR tests twice a week from 7 December 2020 to 5 February 2021, during a time when the Alpha variant (lineage B.1.1.7) was in circulation as the dominant variant. The study compared the positive results for the 90.7% vaccinated share of their cohort with the 9.3% unvaccinated share, and found that the Pfizer-BioNTech vaccine reduced all infections (including asymptomatic), by 72% (58–86%) three weeks after the first dose and 86% (76–97%) one week after the second dose.^{[402][needs update]}
• A study of the general population in Israel conducted from 17 January to 6 March 2021, during a time when the Alpha variant was in circulation as the dominant variant, found that the Pfizer vaccine reduced asymptomatic COVID-19 infections by 94% and symptomatic COVID-19 infections by 97%.^[403]
• A study, among pre-surgical patients across the Mayo Clinic system in the United States, showed that mRNA vaccines were 80% protective against asymptomatic infections.^[404]
• A study in England found that a single dose of the Oxford–AstraZeneca COVID-19 vaccine is about 73% (27–90%) effective in people aged 70 and older.^[405]

Critical coverage

While the most immediate goal of vaccination during a pandemic is to protect individuals from severe disease, a long-term goal is to eventually eradicate it. To do so, the proportion of the population that must be immunized must be greater than the critical vaccination coverage ${\displaystyle V_{c}}$. This value can be calculated from the basic reproduction number ${\displaystyle R_{0}}$ and the vaccine effectiveness against transmission ${\displaystyle E}$ as:^[427]

${\displaystyle V_{c}={\frac {1-1/R_{0}}{E}}}$

Assuming R₀ ≈ 2.87 for SARS-CoV-2,^[428] then, for example, the coverage level would have to be greater than 72.4% for a vaccine that is 90% effective against transmission. Using the same relationship, the required effectiveness against transmission can be calculated as:

${\displaystyle E={\frac {1-1/R_{0}}{V_{c}}}}$

Assuming the same R₀ ≈ 2.87, the effectiveness against transmission would have to be greater than 86.9% for a realistic coverage level of 75%^[348] or 65.2% for an impossible coverage level of 100%. Less effective vaccines would not be able to eradicate the disease.

Several post-marketing studies have already estimated the effectiveness of some vaccines against asymptomatic infection. Prevention of infection has an impact on slowing transmission (particularly asymptomatic and pre-symptomatic), but the exact extent of this effect is still under investigation.^[429]

Some variants of SARS-CoV-2 are more transmissible, showing an increased effective reproduction number, indicating an increased basic reproduction number. Controlling them requires greater vaccine coverage, greater vaccine effectiveness against transmission, or a combination of both.

In July 2021, several experts expressed concern that achieving herd immunity may not currently be possible because the Delta variant is transmitted among those immunized with current vaccines.^[430] The CDC published data showing that vaccinated people could transmit the Delta strain, something officials believed was not possible with other variants.^[431]

Variants

This section's factual accuracy may be compromised due to out-of-date information. The reason given is: Information taken from WHO's COVID-19 Weekly Epidemiological Update is outdated and inaccurate. The latest version now is 20 July, edition 49. Please help update this article to reflect recent events or newly available information. (July 2021)

The interplay between the SARS-CoV-2 virus and its human hosts was initially natural but is now being altered by the prompt availability of vaccines.^[432] The potential emergence of a SARS-CoV-2 variant that is moderately or fully resistant to the antibody response elicited by the COVID-19 vaccines may necessitate modification of the vaccines.^[433] The emergence of vaccine-resistant variants is more likely in a highly vaccinated population with uncontrolled transmission.^[434] Trials indicate many vaccines developed for the initial strain have lower efficacy for some variants against symptomatic COVID-19.^[435] As of February 2021^[update], the US Food and Drug Administration believed that all FDA authorized vaccines remained effective in protecting against circulating strains of SARS-CoV-2.^[433]

Alpha (lineage B.1.1.7)

Limited evidence from various preliminary studies reviewed by the WHO indicated retained efficacy/effectiveness against disease from Alpha with the Oxford–AstraZeneca vaccine, Pfizer–BioNTech and Novavax, with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated retained antibody neutralization against Alpha with most of the widely distributed vaccines (Sputnik V, Pfizer–BioNTech, Moderna, CoronaVac, BBIBP-CorV, Covaxin), minimal to moderate reduction with the Oxford–AstraZeneca and no data for other vaccines yet.^[436]

In December 2020, a new SARS‑CoV‑2 variant, the Alpha variant or lineage B.1.1.7, was identified in the UK.^[437]

Early results suggest protection to the variant from the Pfizer-BioNTech and Moderna vaccines.^[438][439]

One study indicated that the Oxford–AstraZeneca COVID-19 vaccine had an efficacy of 42–89% against Alpha, versus 71–91% against other variants.^{[440][unreliable medical source?]}

Preliminary data from a clinical trial indicates that the Novavax vaccine is ~96% effective for symptoms against the original variant and ~86% against Alpha.^[441]

Beta (lineage B.1.351)

Limited evidence from various preliminary studies reviewed by the WHO have indicated reduced efficacy/effectiveness against disease from Beta with the Oxford–AstraZeneca vaccine (possibly substantial), Novavax (moderate), Pfizer–BioNTech and Janssen (minimal), with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated possibly reduced antibody neutralization against Beta with most of the widely distributed vaccines (Oxford–AstraZeneca, Sputnik V, Janssen, Pfizer–BioNTech, Moderna, Novavax; minimal to substantial reduction) except CoronaVac and BBIBP-CorV (minimal to modest reduction), with no data for other vaccines yet.^[436]

Moderna has launched a trial of a vaccine to tackle the Beta variant or lineage B.1.351.^[442] On 17 February 2021, Pfizer announced neutralization activity was reduced by two-thirds for this variant, while stating that no claims about the efficacy of the vaccine in preventing illness for this variant could yet be made.^[443] Decreased neutralizing activity of sera from patients vaccinated with the Moderna and Pfizer-BioNTech vaccines against Beta was later confirmed by several studies.^[439][444] On 1 April 2021, an update on a Pfizer/BioNTech South African vaccine trial stated that the vaccine was 100% effective so far (i.e., vaccinated participants saw no cases), with six of nine infections in the placebo control group being the Beta variant.^[445]

In January 2021, Johnson & Johnson, which held trials for its Janssen vaccine in South Africa, reported the level of protection against moderate to severe COVID-19 infection was 72% in the United States and 57% in South Africa.^[446]

On 6 February 2021, the Financial Times reported that provisional trial data from a study undertaken by South Africa's University of the Witwatersrand in conjunction with Oxford University demonstrated reduced efficacy of the Oxford–AstraZeneca COVID-19 vaccine against the variant.^[447] The study found that in a sample size of 2,000 the AZD1222 vaccine afforded only "minimal protection" in all but the most severe cases of COVID-19.^[448] On 7 February 2021, the Minister for Health for South Africa suspended the planned deployment of about a million doses of the vaccine whilst they examine the data and await advice on how to proceed.^[448][449]

In March 2021, it was reported that the "preliminary efficacy" of the Novavax vaccine (NVX-CoV2373) against Beta for mild, moderate, or severe COVID-19^[450] for HIV-negative participants is 51%.

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "COVID-19 vaccine clinical research" – news · newspapers · books · scholar · JSTOR (June 2021) (Learn how and when to remove this message)

Gamma (lineage P.1)

Limited evidence from various preliminary studies reviewed by the WHO have indicated likely retained efficacy/effectiveness against disease from Gamma with CoronaVac and BBIBP-CorV, with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated retained antibody neutralization against Gamma with Oxford–AstraZeneca and CoronaVac (no to minimal reduction) and slightly reduced neutralization with Pfizer–BioNTech and Moderna (minimal to moderate reduction), with no data for other vaccines yet.^[436]

The Gamma variant or lineage P.1 variant (also known as 20J/501Y.V3), initially identified in Brazil, seems to partially escape vaccination with the Pfizer-BioNTech vaccine.^[444]

Delta (lineage B.1.617.2)

Limited evidence from various preliminary studies reviewed by the WHO have indicated likely retained efficacy/effectiveness against disease from Delta with the Oxford–AstraZeneca vaccine and Pfizer–BioNTech, with no data for other vaccines yet. Relevant to how vaccines can end the pandemic by preventing asymptomatic infection, they have also indicated reduced antibody neutralization against Delta with single-dose Oxford–AstraZeneca (substantial reduction), Pfizer–BioNTech and Covaxin (modest to moderate reduction), with no data for other vaccines yet.^[436]

In October 2020, a new variant was discovered in India, which was named

Side effects

This section needs expansion. You can help by adding to it. (July 2021)

Serious adverse events associated with receipt of new vaccines targeting COVID-19 are of high interest to the public.[461] All vaccines that are administered via intramuscular injection, including COVID-19 vaccines, have side effects related to the mild trauma associated with the procedure and introduction of a foreign substance into the body.^[462] These include soreness, redness, rash, and inflammation at the injection site. Other common side effects include fatigue, headache, myalgia (muscle pain), and arthralgia (joint pain) which generally resolve within a few days.^[463] One less-frequent side effect (that generally occurs in less than 1 in 1,000 people) is hypersensitivity (allergy) to one or more of the vaccine's ingredients, which in some rare cases may cause anaphylaxis.^{[464][465][466][467]} More serious side effects are very rare because a vaccine would not be approved even for emergency use if it had any known frequent serious adverse effects.^{[citation needed]}

Reporting

Most countries operate some form of adverse effects reporting scheme, for example Vaccine Adverse Event Reporting System in the United States and the Yellow Card Scheme^[468] in the United Kingdom. In some of these, the data is open to public scrutiny, for example, in the UK, a weekly summary report is published.^[469] Concerns have been raised regarding both over-^[470] and under-reporting^{[citation needed]} of adverse effects.

UK

In the UK, as of 22 September 2021, following the administering of over 48 million first vaccine doses and over 44 million second vaccine doses, there had been 347,447 suspected Covid-19 vaccine related events ('suspected adverse reactions', or 'ADRs') recorded in the Yellow Card system. The majority of these were reports of relatively minor effects (local reactions or temporary flu-like symptoms). Among more serious ADRs, the largest case load came from suspected thrombo-embolic events, of which a total of 439 were recorded, 74 of these fatal.^[469] A total of 1,682 suspected fatal ADRs were recorded.^[469] For comparison, at this date, the UK had had over 7,500,000 confirmed cases of Covid-19 and over 136,000 people had died within 28 days of a positive test for coronavirus.^[469]

Embolic and thrombotic events

The Janssen COVID-19 vaccine reported rare

In a study on the serologic response to COVID-19 messenger RNA vaccines among patients with lymphoma, leukemia and myeloma, it was found that one-quarter of patients did not produce measurable antibodies, varying by blood cancer type. Patients with these conditions need to take precautions to avoid exposure to COVID-19.[474]

References