SARS-CoV-2 Omicron variant

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(Redirected from
Lineage B.1.1.529
)

— less common
Major variants

Omicron (B.1.1.529) is a

BQ.1.1
have emerged.

Three doses of a COVID-19 vaccine provide protection against severe disease and hospitalisation caused by Omicron and its subvariants.[14][15][16][17] For three-dose vaccinated individuals, the BA.4 and BA.5 variants are more infectious than previous subvariants but there is no evidence of greater sickness or severity.[13][18][19]

Classification

SARS-CoV-2 depicted in a tree scaled radially by genetic distance, derived from Nextstrain
on 1 December 2021

On 26 November 2021, the

Greek letter omicron.[10] The WHO skipped the preceding letters nu and xi in the Greek alphabet to avoid confusion with the similarities of the English word "new" and the Chinese surname Xi.[20]

The name of the variant has occasionally been mistaken as "Omnicron" among some English speakers, due to a lack of familiarity with the Greek alphabet, and the relative frequency of the Latin prefix "omni" in other common speech.[21][22]

The GISAID project has assigned it the clade identifier GR/484A,[23] and the Nextstrain project has assigned it the clade identifiers 21K and 21L, both belonging to a larger Omicron group 21M.[24]

History

Omicron was first detected on 22 November 2021 in laboratories in

variant of concern and named it "Omicron", after the fifteenth letter in the Greek alphabet.[10] As of 6 January 2022, the variant had been confirmed in 149 countries.[29]

Origin hypotheses

Omicron did not evolve from any other variant, but instead diverged on a distinct track, perhaps in mid-2020.[29][30] Competing hypotheses are being examined.

One origin hypothesis is that various mutations in the Omicron variant, comprising a 9-

HCoV-229E), responsible for the common cold.[31] This is not entirely unexpected — at times, viruses within the body acquire and swap segments of genetic material from each other, and this is one common means of mutation.[31]

A link with HIV infection may explain a large number of mutations in the sequence of the Omicron variant.[32] Indeed, in order to be affected by such a high number of mutations, the virus must have been able to evolve a long time without killing its host, which can occur in people with a weakened immune system who receive enough medical care to survive.[32][33] This is the case in HIV patients in South Africa, who represent about 14% of the population (as of 2017).[34] HIV prevention could be key to reducing the risk of uncontrolled HIV driving the emergence of SARS-CoV-2 variants.[32]

One hypothesis to explain the novel mutations is that SARS-CoV-2 was transmitted from humans to mice and mutated in a population of mice sometime between mid-2020 and late 2021 before reinfecting humans.[30]

On 1 December 2022, a team of researchers from the Charité (Berlin) published a now-retracted study in Science (journal) that claimed that "data revealed genetically diverse Omicron ancestors already existed across Africa by August 2021".[35] After a re-analysis because of doubts,[36] the team retracted the article on 20 December 2022 due to contamination of the samples.[37][38]

Spread

On 24 November 2021, the variant was first reported to the WHO from South Africa based on samples that had been collected from 14 to 16 November.[25] South African scientists were first alerted by samples from the very beginning of November where the PCR tests had S gene target failure (occurs in a few variants, but not in Delta which dominated in the country in October) and by a sudden increase of COVID-19 cases in Gauteng; sequencing revealed that more than 70 percent of samples collected in the province between 14 and 23 November were a new variant.[39]

The first confirmed specimens of Omicron were collected on 8 November 2021 in South Africa and on 9 November in Botswana.[40] Likely Omicron (SGTF) samples had occurred on 4 November 2021 in Pretoria, South Africa.[citation needed]

When WHO was alerted on 24 November, Hong Kong was the only place outside Africa that had confirmed a case of Omicron; one person who traveled from South Africa on 11 November, and another traveler who was cross-infected by this case while staying in the same quarantine hotel.[27]

On 25 November, one confirmed case was identified in Israel from a traveler returning from Malawi,[41] along with two who returned from South Africa and one from Madagascar.[42] All four initial cases reported from Botswana occurred among fully vaccinated individuals.[43]

On 26 November, Belgium confirmed its first case; an unvaccinated person who had travelled from Egypt via Turkey on 11 November.[28] All three initial confirmed and suspected cases reported from Israel occurred among fully vaccinated individuals,[41] as did a single suspected case in Germany.[44]

On 27 November, two cases were detected in the United Kingdom, another two in Munich, Germany and one in Milan, Italy.[45]

On 28 November, 13 cases were confirmed in the Netherlands among the 624 airline passengers who arrived from South Africa on 26 November.

Doha Airport. The two people, who were fully vaccinated, entered isolation; 12 other travellers from southern Africa also entered quarantine for fourteen days, while about 260 other passengers and crew on the flight were directed to isolate.[49] Two travellers from South Africa who landed in Denmark tested positive for COVID-19; it was confirmed on 28 November that both carried the Omicron variant.[50][51] On the same day, Austria also confirmed its first Omicron case.[52] A detected Omicron case was reported in the Czech Republic, from a traveler who spent time in Namibia.[53] Canada also reported its first Omicron cases, with two from travelers from Nigeria, therefore becoming the first North American country to report an Omicron case.[54]

On 29 November, a positive case was recorded in Darwin, Australia. The person arrived in Darwin on a repatriation flight from Johannesburg, South Africa on 25 November, and was taken to a quarantine facility, where the positive test was recorded.[55] Two more people who travelled to Sydney from southern Africa via Singapore tested positive.[56] Portugal reported 13 Omicron cases, all of them members of a soccer club.[57] Sweden also confirmed their first case on 29 November,[58] as did Spain, when a traveler came from South Africa.[59]

On 30 November, the Netherlands reported that Omicron cases had been detected in two samples dating back as early as 19 November.[60] A positive case was recorded in Sydney from a traveller who had visited southern Africa before travel restrictions were imposed, and was subsequently active in the community.[61] Japan also confirmed its first case.[62] Two Israeli doctors tested positive and entered isolation. Both of them had received three shots of the Pfizer vaccine prior to testing positive.[63] In Brazil, three cases of the Omicron variant were confirmed in São Paulo.[64] Another five are under suspicion.[65][66] A person in Leipzig, Germany with no travel history nor contact with travellers tested positive for Omicron.[67]

On 1 December, the Omicron variant was detected in three samples in Nigeria that had been collected from travelers from South Africa within the last week.[68][69] On the same day, public health authorities in the United States announced the country's first confirmed Omicron case. A resident of San Francisco who had been vaccinated returned from South Africa on 22 November, began showing mild symptoms on 25 November[70] and was confirmed to have a mild case of COVID-19 on 29 November.[71] Ireland and South Korea also reported their first cases.[72] South Korea reported its cases from five travelers arriving in South Korea from Nigeria.[73]

On 2 December, Dutch health authorities confirmed that all 14 passengers with confirmed Omicron infection on 26 November had been previously vaccinated.[74] The same day, the Norwegian Institute of Public Health confirmed that 50 attendees of a company Christmas party held at a restaurant in Norway's capital, Oslo, were infected with the Omicron variant.[75] France has confirmed only 25 cases of the new Omicron variant but officials say the number could jump significantly in the coming weeks.[76]

By 6 December, Malaysia confirmed its first case of the variant. The case was a South African student entering to study at a private university.[77] In Namibia, 18 cases out of 19 positive COVID-19 samples that had been collected between 11 and 26 November were found to be Omicron, indicating a high level of prevalence in the country.[78] Fiji also confirmed two positive cases of the variant. They travelled from Nigeria arriving in Fiji on November 25.[79]

On 9 December, Richard Mihigo, coordinator of the World Health Organisation's Immunisation and Vaccine Development Programme for Africa, announced that Africa accounted for 46% of reported cases of the Omicron variant globally.[80]

On 13 December, the first death of a person with Omicron was reported in the UK.[81]

On 16 December, New Zealand confirmed its first case of the Omicron variant, an individual who had traveled from Germany via Dubai.[82]

The first death of a person with Omicron was reported in Germany on 23 December[83] and in Australia on 27 December.[84]

By Christmas 2021, the Omicron Strain became dominant in the US.[85]

On 3 January 2022, South Korea reported the first two deaths of people who tested positive

post mortem for Omicron.[86]

In February 2022, Omicron accounted for 98% of publicly available genetic sequences worldwide.[87]

On 29 March 2022, Omicron subvariant BA.2 overtook BA.1 and became the dominant strain in the U.S.[88][89][90]

As of May 2022, BA.2.12.1 was spreading in the US and two new subvariants of Omicron named BA.4 and BA.5, first detected in January 2022, spread in South Africa. All 3 subvariants have spike protein mutations of L452 and elude immunity from prior BA1 infection.[91]

On 16 March 2023, without seeing a reduction in the threat to public health, the WHO stopped classifying Omicron as a variant of concern in order to maintain this classification only for new threats. Instead, the WHO classified its subvariants as variants of interest and under monitoring.[87]

Reactions

Vaccine producers

On 26 November 2021,

Sinovac said it could quickly mass-produce an inactivated vaccine against the variant and that it was monitoring studies and collecting samples of the variant to determine if a new vaccine is needed.[96]

On 7 December 2021, at a symposium in Brazil with its partner Instituto Butantan, Sinovac said it would update its vaccine to the new variant and make it available in three months.[97] On 2 December, the Finlay Institute was already developing a version of Soberana Plus against the variant.[98] Pfizer hoped to have a vaccine targeted to immunize against Omicron ready by March 2022.[99]

World Health Organization

On 26 November 2021, the WHO asked nations to enhance surveillance and sequencing efforts, submit complete genome sequences and associated metadata to a publicly available database, such as GISAID, report initial cases/clusters associated with virus-of-concern infection to WHO through the IHR mechanism, where capacity exists and in coordination with the international community, perform field investigations and laboratory assessments to improve understanding of the potential impacts of the virus of concern on COVID-19 epidemiology, severity, and the effectiveness of public health and social measures, diagnostic methods, immune responses, antibody neutralization, or other relevant characteristics.[100] On 26 November 2021, WHO advised countries not to impose new restrictions on travel, instead recommending a "risk-based and scientific" approach to travel measures.[101] On the same day, the European Centre for Disease Prevention and Control (ECDC) reported modeling indicating that strict travel restrictions would delay the variant's impact on European countries by two weeks, possibly allowing countries to prepare for it.[102] As with other variants, the WHO recommended that people continue to keep enclosed spaces well ventilated, avoid crowding and close contact, wear well-fitting masks, clean hands frequently, and get vaccinated.[103][104] On 29 November 2021, the WHO said cases and infections were expected among those vaccinated, albeit in a small and predictable proportion.[105]

International response

After the WHO announcement, on the same day, several countries announced travel bans from southern Africa in response to the identification of the variant, including the United States, which banned travel from eight African countries,[106] although as of 30 November 2021 it notably did not ban travel from any European countries, Israel, Canada, or Australia where cases were also detected at the time the bans were announced. Other countries that also implemented travel bans include Japan, Canada, the European Union, Israel, Australia, the United Kingdom, Singapore, Malaysia, Indonesia, Morocco, and New Zealand.[107][108]

On 26 November 2021 the Brazilian Health Regulatory Agency recommended flight restrictions regarding the new variant.[109] The state of New York declared a state of emergency ahead of a potential Omicron spike, although no cases had yet been detected in the state or the rest of the United States.[110] On 27 November 2021, Switzerland introduced obligatory tests and quarantine for all visitors arriving from countries where the variant was detected, which originally included Belgium and Israel.[111]

On 26 November 2021 South African Minister of Health Joe Phaahla defended his country's handling of the pandemic and said that travel bans went against the "norms and standards" of the World Health Organization.[112]

Some speculated that

intellectual property to develop and produce vaccines locally.[113] At the same time, inoculation had slowed in South Africa due to vaccine hesitancy and apathy, with a nationwide vaccination rate of only 35% as of November 24, 2021.[114]

On 29 November 2021, the WHO warned countries that the variant poses a very high global risk with severe consequences and that they should prepare by accelerating vaccination of high-priority groups and

strengthening health systems. WHO director-general Tedros Adhanom described the global situation as dangerous and precarious and called for a new agreement on the handling of pandemics, as the current system disincentivizes countries from alerting others to threats that will inevitably land on their shores. CEPI CEO Richard Hatchett said that the variant fulfilled predictions that transmission of the virus in low-vaccination areas would accelerate its evolution.[105]

In preparation for the Omicron variant arriving in the United States, President Joe Biden stated that the variant is "cause for concern, not panic", reiterated that the government was prepared for the variant and would have it under control and that large-scale lockdowns, similar to the ones in 2020 near the beginning of the pandemic, were "off the table for now."[115]

In mid-December 2021, multiple Canadian provinces reinstated restrictions on gatherings and events such as sports tournaments, and tightened enforcement of

proof of vaccination orders. British Columbia expressly prohibited any non-seated "organized New Year's Eve event",[116][117][118] while Quebec announced a partial lockdown on 20 December 2021, ordering the closure of all bars, casinos, gyms, schools, and theatres, as well as imposing restrictions on the capacity and operating hours of restaurants, and the prohibition of spectators at professional sporting events.[119]

On 18 December 2021, the Netherlands government announced a lockdown intended to prevent spread of the variant during the holiday period.[120]

In late December 2021, some countries shortened the typical six-month interval for a booster dose of the vaccine to prepare for a wave of Omicron, as two doses are not enough to stop the infection. UK, South Korea and Thailand reduced to three months; Belgium, four months; France, Singapore, Taiwan, Italy and Australia, five months. Finland reduced it to three months for risk groups. Other countries continued with a six-month booster schedule. While antibody levels begin to drop at four months, a longer interval usually allows time for the immune system's response to mature.[121]

Market reactions

On 26 November 2021, worry about the potential economic impact of the Omicron variant led to a drop in global markets, including the worst drop of the Dow Jones Industrial Average in 2021, led by travel-related stocks. The price of Brent Crude and West Texas Intermediate oil fell 10% and 11.7%, respectively[122] Cryptocurrency markets were also routed.[123][124] and the South African rand also hit an all-time low for 2021, trading at over 16 rand to the dollar, losing 6% of its value in November.[125][126][127]

In early December 2021,

U.S. Senate Committee on Banking that "The recent rise in COVID-19 cases and the emergence of the Omicron variant pose downside risks to employment and economic activity and increased uncertainty for inflation."[128]

Biology

The genomic sequence of the Omicron variant is pictured above

Mutations

As of June 2022, Omicron had about 50 mutations relative to the Wuhan-Hu-1 or B variant,

cleavage site, which facilitates its transmission.[133][134]

WHO,[103] structure from PDB: 6VYB​.[135]
Mutation prevalence across Omicron lineages
Comparison of mutation prevalence for ORF1a, ORF1b, and S genes of Omicron lineages that are designated Variants of Concern. Characteristic mutations for a lineage are defined as nonsynonymous substitutions or deletions that occur in > 75% of sequences within that lineage.[136]

Subvariants

Several subvariants of Omicron have been discovered and new ones continue to emerge.[12] There are 310 Pango lineages[clarification needed] currently associated with the Omicron variant.[137] The 'standard' sublineage is now referred to as BA.1 (or B.1.1.529.1), and the two other sublineages are known as BA.2 (or B.1.1.529.2) and BA.3 (or B.1.1.529.3).[138] In mid-2022, BA.4 (or B.1.1.529.4) and BA.5 (or B.1.1.529.5) were detected in several countries.[139] They share many mutations, but also significantly differ. In general, BA.1 and BA.2 share 32 mutations, but differ by 28.[140] BA.1 has itself been divided in two, the original BA.1 and BA.1.1 (or B.1.1.529.1.1) where the main difference is that the latter has a R346K mutation.[141]

Standard PCR and rapid tests continue to detect all Omicron subvariants as COVID-19, but further tests are necessary to distinguish the subvariants from each other and from other COVID-19 variants.[142]

Defining mutations in the
SARS-CoV-2 Omicron variant
Gene Amino acid
ORF1ab nsp3: K38R
nsp3: V1069I
nsp3: Δ1265
nsp3: L1266I
nsp3: A1892T
nsp4: T492I
nsp5: P132H
nsp6: Δ105-107
nsp6: A189V
nsp12: P323L
nsp14: I42V
Spike A67V
Δ69-70
T95I
G142D,
Δ143-145
Δ211
L212I
ins214EPE
G339D
S371L
S373P
S375F
K417N
N440K
G446S
S477N
T478K
E484A
Q493R
G496S
Q498R
N501Y
Y505H
T547K
D614G
H655Y
N679K
P681H
N764K
D796Y
N856K
Q954H
N969K
L981F
E T9I
M D3G
Q19E
A63T
N P13L
Δ31-33
R203K
G204R
Sources: UK Health Security Agency[143] CoVariants[24]

BA.2

BA.2 was first detected in a sample from 15 November 2021.[144] A preprint released in February 2022 (published in May) suggested that BA.2 was more transmissible than BA.1 and may cause more severe disease.[145] This was later disproven by a study in late-October 2022, that found BA.2 actually caused less severe disease relative to BA.1 (which in turn, caused less severe disease compared to the delta variant).[146] Therapeutic monoclonal antibodies used to treat people infected with COVID-19 did not have much effect on BA.2, which was "almost completely resistant" to casirivimab and imdevimab, and 35 times more resistant to sotrovimab than the BA.1 subvariant.[citation needed]

Spread

As of 17 January 2022, BA.2 had been detected in at least 40 countries and in all continents except Antarctica.[147] By 31 January, it had been detected in at least 57 countries.[148] In global samples collected from 4 February to 5 March and uploaded to GISAID, BA.2 accounted for c. 34%, compared to 41% for BA.1.1, 25% for BA.1 and less than 1% for BA.3.[149] In a review two weeks later, covering 16 February to 17 March, BA.2 had become the most frequent.[150][151] Based on GISAID uploads, BA.1 peaked in early January 2022, after which it was overtaken by both BA.1.1 and BA.2.[152] In North America, parts of Europe and parts of Asia, BA.1 was first outcompeted by BA.1.1. For example, in the United States, France and Japan, BA.1.1 became the dominant subvariant in January 2022.[153][154][155]

By late December 2021/early January 2022, BA.2 had become dominant in parts of India (already making up almost 80 percent in Kolkata in late December 2021[156]) and the Philippines, had become frequent in Scandinavia, South Africa and Singapore, and was showing signs of growth in Germany and the United Kingdom.[157][158][159][160] In Japan, which has quarantine and detailed screening of all international travellers, as of 24 January, the vast majority of BA.2 had been detected in people that had arrived from India or the Philippines with cases going back at least to 1 December 2021 (far fewer BA.1 or other variants were detected among arrivals from the two countries in that period), but small numbers had also been detected in people arriving from other countries.[161][162][163]

In Denmark, the first BA.2 was in a sample collected on 5 December 2021.[164] By week fifty (13–19 December) it had started to increase, with BA.2 being at around 2 percent of sequenced cases compared to 46 percent BA.1 (remaining Delta). The frequency of both Omicron subvariants continued to increase throughout the last half of December; and by the end of the year BA.2 had reached 20 percent and BA.1 peaked at 72 percent. In January 2022, BA.1 began decreasing, whereas BA.2 continued its increase. By the second week of 2022, the frequency of the two was almost equal, both being near 50 percent.[164] In the following week, BA.2 became clearly dominant in Denmark with 65 percent of new cases.[165] Trends from the other Scandinavian countries, India, South Africa and the United Kingdom also showed that BA.2 was increasing in proportion to BA.1.[166][167] In early February 2022, it had become the dominant subvariant in South Africa, in late February it had become dominant in Germany and in early March it had become dominant in the United Kingdom.[168][169][170] In early March, BA.1.1 was still heavily dominant in the United States (having overtaken BA.1 in January), but BA.2 was increasing in frequency, later becoming dominant in the US by 29 March.[153][171]

XE

A new BA.1–BA.2 recombinant was isolated in the UK in January 2022, dubbed the "XE" recombinant. It was found by the WHO to be potentially 10% more transmissible than BA.2, making it about 43% to 76% to more transmissible than BA.1, and making the XE recombinant the most contagious variant identified at the time.[172]

BA.2.12

There were two new BA.2 subvariants detected in the US state of New York, which are BA.2.12 (or B.1.1.529.2.12) and BA.2.12.1 (or B.1.1.529.2.12.1), both of which have a significant growth advantage of 23–27% over BA.2 and contributing to a rise in infections in central New York, centred on Syracuse and Lake Ontario, which later became dominant by May 24, 2022, in the US.[173]

BA.2.75 and BA.2.75.2

The subvariant BA.2.75 (or B.1.1.529.2.75, nicknamed Centaurus by the media[174]), first detected in India in May 2022, was classified as variant under monitoring by the WHO.[175] Additional newer mutations in this line (like BA.2.75.2 aka B.1.1.529.2.75.2 or Chiron) may be capable of escaping neutralizing antibodies.[176]

XBB and XBB.1

XBB, a recombinant of the BA.2.10.1.1 and BA.2.75.3.1.1.1 sublineages,[177] is an Omicron subvariant first detected in August 2022.[178]

On 20 October 2022, the chief scientist of the World Health Organization (WHO), Soumya Swaminathan, warned that the XBB subvariant of Omicron may cause infections in some countries while the severity of the new variants is not yet known.[179]

On 9 January 2023 the

European CDC said there was suggestive evidence the XBB.1.5 variant had a growth advantage; after becoming dominant in the US, it might become dominant in Europe in the following months.[180] From preliminary evidence, they had assessed the XBB variants had no effect on disease severity and transmissibility.[181]

In early March 2023, XBB.1.16 first appeared in India and caused a surge of hospitalizations.

EG.5 and EG.5.1

EG.5 (or XBB.1.9.2.5), nicknamed by some media "Eris",[185] is a descendant of XBB.1.9.2. The lineage was detected as early as February 2023.[186] On 6 August, the UK Health Security Agency reported the EG.5 strain was responsible for one in seven new cases in the UK during the third week of July.[187] It was identified as a "variant of interest" by the WHO on 9 August 2023. Its key difference from other strains is a "F456L amino acid mutation".[188]

HV.1

HV.1 (or XBB.1.9.2.5.1.6.1) is a sublineage of XBB.1.9.2, of the Omicron family first detected in July 2023.

HV.1 overtook EG.5 as the dominant subvariant in the U.S. in October 2023.[189] In October experts stated that there was no evidence that HV.1 was more severe or transmissible than other Omicron subvariants.[190]

BA.2.86

In mid-August 2023, the CDC and WHO announced they were monitoring another subvariant of Omicron, BA.2.86, a descendant of the BA.2 subvariant. The WHO has placed BA.2.86 as a VUM (variant under monitoring) as it is reported to have more than 30 mutations.[191] As of 18 August, cases had been reported from four countries: three in Denmark and a single each in Israel, the UK and the US. On the same date, UK healthcare authorities noted that its almost simultaneous appearance in several countries still operating detailed genomic surveillance indicated that it likely already was spreading more widely internationally.[192] The first case of BA.2.86 was collected on 24 July 2023 according to the WHO.

BA.3

The third Omicron sublineage, BA.3, is very rare. It has the same S-gene target failure (SGTF) deletion (Δ69-70) as BA.1.[citation needed]

BA.4 and BA.5

In April 2022, the WHO announced it was tracking the BA.4 and BA.5 subvariants with BA.4 having been detected in South Africa, Botswana, Denmark, Scotland and England.[193] Early indications from data collected in South Africa suggested BA.4 and BA.5 have a significant growth advantage over BA.2, which by 12 May earned the status Variant of Concern by the European Centre for Disease Prevention and Control, and, by 20 May, by the UK Health Security Agency.[194][195][196][197] BA.5 was dominant in Portugal by 25 May, accounting for two-thirds of all new cases there.[198] By 24 June, BA.4 and BA.5 together had become dominant variants in the UK and Germany.[199][200][201][202] These two subvariants became dominant in the United States by 28 June.[203][204] By late June, BA.5 became the dominant subvariant in France, with 59% of new cases linked to it.[205][206]

On 10 May 2022, a case of a new subvariant BA.5.2.1 was reported in California.[207] On 10 July, the city of Shanghai reported its first case of BA.5.2.1, in a man who had flown in from Uganda, sparking a new wave of testing.[208] On 22 July, the province of Ontario, Canada announced that subvariant BA.5.2.1 overtook BA.2.12.1 as the main variant in circulation in Ontario around 2 July.[209] Regeneron is reporting that BA.5.2.1 is the main variant in Australia, Belgium, Brunei, Greece and Iceland.[210] The government of Canada also reported in late June and July, of the travelers arriving by air who test positive for COVID-19, a substantial proportion were BA.5.2.1.[211] BF.7 is a shortened version of the sub-variants full name, which is BA.5.2.1.7. This sub-variant is part of Omicron's BA.5 variant, which had the highest number of reported cases globally, accounting for 76.2% of all cases.[212]

BQ.1 and BQ.1.1

In October 2022, two BA.5 subvariants were found: BQ.1 (or B.1.1.529.5.3.1.1.1.1.1) and BQ.1.1 (or B.1.1.529.5.3.1.1.1.1.1.1).[213][214][215] The variants were originally most prevalent in France.[216] As of 17 November, 93% of sequences in France were Omicron sub-lineage BA.5 and among the BA.5 sub-lineages, BQ.1.1 continued to rise (32% vs 25% in the prior week).[217] In November 2022 in the US it was reported the variants were accounting for 44% of new infections. Early laboratory tests found that these subvariants were better at escaping first and booster vaccines than previous variants.[218]

Transmission

False-color transmission electron micrograph of an Omicron variant coronavirus, shown in pink, replicating within the cytoplasm of an infected Vero cell

In humans

In January 2022, William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, compared the contagiousness of the Omicron variant to that of the measles.[219]

On 15 December 2021, Jenny Harries, head of the UK Health Security Agency, told a parliamentary committee that the doubling time of COVID-19 in most regions of the UK was now less than two days despite the country's high vaccination rate. She said that the Omicron variant of COVID-19 is "probably the most significant threat since the start of the pandemic", and that the number of cases in the next few days would be "quite staggering compared to the rate of growth that we've seen in cases for previous variants".[220]

A 2021 study suggested that mutations that promote breakthrough infections or antibody-resistance "like those in Omicron" could be a new mechanism for viral evolution success of SARS-CoV-2 and that such may become a dominating mechanism of its evolution.[221] A preprint supports such an explanation of Omicron's spread, suggesting that it "primarily can be ascribed to the immune evasiveness rather than an inherent increase in the basic transmissibility".[222][223] Studies showed the variant to escape the majority of existing SARS-CoV-2 neutralizing antibodies, including those in sera from vaccinated and convalescent individuals.[224][225][226][227] Nevertheless, existing vaccines were expected to protect against severe illness, hospitalizations, and deaths due to Omicron[228] and, on an individual level, the Omicron variant is milder than earlier variants that evolved when the antibody/vaccination share was lower than it was when Omicron emerged.[229]

In contrast to other investigated variants, Omicron showed substantial, population-level, evasion of immunity from prior infection as well as a higher ability to evade immunity induced by vaccines.[230]

Later research found that the spread of Omicron likely contributed to significant natural immunity to reinfection.[231]

In non-human animals

In February 2022, the first confirmed case infecting a wild animal was confirmed by researchers at Pennsylvania State University in white-tailed deer in Staten Island, N.Y.[232]

Surfaces

Although transmission via fomites is rare, preliminary data indicate that the variant lasts for 194 hours on plastic surfaces and 21 hours on skin, compared with just 56 and 7 hours, respectively, for the original strain.[233][234]

Vaccine effectiveness

Pfizer-BioNTech (BNT162b2) and Moderna (mRNA-1273) mRNA vaccines provide reduced protection against asymptomatic disease but do reduce the risk of serious illness.[235][236][237] On 22 December 2021, the Imperial College COVID-19 Response Team reported an about 41% (95% CI, 3745%) lower risk of a hospitalization requiring a stay of at least 1 night compared to the Delta variant, and that the data suggested that recipients of 2 doses of the Pfizer–BioNTech, the Moderna or the Oxford–AstraZeneca vaccine were substantially protected from hospitalization.[238] In January 2022, results from Israel suggested that a fourth dose is only partially effective against Omicron. Many cases of infection broke through, albeit "a bit less than in the control group", even though trial participants had higher antibody levels after the fourth dose.[239] On 23 December 2021, Nature indicates that, though Omicron likely weakens vaccine protection, reasonable effectiveness against Omicron may be maintained with currently available vaccination and boosting approaches.[240][241]

In December, studies, some of which using large nationwide datasets from either Israel and Denmark, found that

Delta variant, and that a new (often a third) dose – a booster dose – is needed and effective, as it substantially reduces deaths from the disease compared to cohorts who received no booster but two doses.[242][243][244][245][246][247]

Vaccines continue to be recommended for Omicron and its subvariants. Professor Paul Morgan,

Francois Balloux of the Genetics Institute at University College London said, "From what we have learned so far, we can be fairly confident that – compared with other variants – Omicron tends to be better able to reinfect people who have been previously infected and received some protection against COVID-19. That is pretty clear and was anticipated from the mutational changes we have pinpointed in its protein structure. These make it more difficult for antibodies to neutralise the virus."[249]

BA.1 and BA.2

A January 2022 study by the UK Health Security Agency found that vaccines afforded similar levels of protection against symptomatic disease by BA.1 and BA.2, and in both it was considerably higher after two doses and a booster than two doses without booster,[250][251] though because of the gradually waning effect of vaccines, further booster vaccination may later be necessary.[170]

BA.4 and BA.5

In May 2022, a

reinfections, beyond the increase of reinfections caused by the Omicron lineage, even for people who were infected by Omicron BA.1 due to increases in immune evasion, especially for the unvaccinated. However, the observed escape of BA.4 and BA.5 from immunity by a BA.1 infection is more moderate than of BA.1 against studied prior cases of immunity (such as immunity from specific vaccines).[252][253]

Immunity from an Omicron infection for unvaccinated and previously uninfected was found to be weak "against non-Omicron variants",[254] albeit at the time Omicron is, by a large margin, the dominant variant in sequenced human cases.[255]

BQ.1 and BQ.1.1

Subvariants BQ.1 and BQ.1.1 were found in late 2022 to be better at escaping first and booster vaccines than previous variants, and to have further reduced the effectiveness of monoclonal antibody treatments.[256]

Vaccine adjustments

In June 2022,

bivalent vaccines to protect against the SARS-CoV-2 wild-type and the Omicron variant. The bivalent vaccines are well-tolerated and offer immunity to Omicron superior to previous mRNA vaccines.[257] In September 2022, the United States Food and Drug Administration (FDA) authorized the bivalent vaccines for use in the US.[258][259][260]

In June 2023, the FDA advised manufacturers that the 2023–2024 formulation of the COVID-19 vaccines for use in the US be updated to be a monovalent COVID-19 vaccine using the XBB.1.5 lineage of the Omicron variant.[261][262]

Signs and symptoms