Oct. 28, 2022

As part of its ongoing work to track variants, WHO's Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE) met on the 24 October 2022 to discuss the latest evidence on the Omicron variant of concern, and how its evolution is currently unfolding, in light of high levels of population immunity in many settings and country differences in the immune landscape. In particular, the public health implications of the rise of some Omicron variants, specifically XBB and its sublineages (indicated as XBB*), as well as BQ.1 and its sublineages (indicated as BQ.1*), were discussed.

Based on currently available evidence, the TAG-VE does not feel that the overall phenotype of XBB* and BQ.1* diverge sufficiently from each other, or from other Omicron lineages with additional immune escape mutations, in terms of the necessary public health response, to warrant the designation of new variants of concern and assignment of a new label.

The two sublineages remain part of Omicron, which continues to be a variant of concern.

This decision will be reassessed regularly. If there is any significant development that warrant a change in public health strategy, WHO will promptly alert Member States and the public.


XBB* is a recombinant of BA.2.10.1 and BA.2.75 sublineages. As of epidemiological week 40 (3 to 9 October), from the sequences submitted to GISAID, XBB* has a global prevalence of 1.3% and it has been detected in 35 countries. The TAG-VE discussed the available data on the growth advantage of this sublineage, and some early evidence on clinical severity and reinfection risk from Singapore and India, as well as inputs from other countries. There has been a broad increase in prevalence of XBB* in regional genomic surveillance, but it has not yet been consistently associated with an increase in new infections. While further studies are needed, the current data do not suggest there are substantial differences in disease severity for XBB* infections. There is, however, early evidence pointing at a higher reinfection risk, as compared to other circulating Omicron sublineages. Cases of reinfection were primarily limited to those with initial infection in the pre-Omicron period. As of now, there are no data to support escape from recent immune responses induced by other Omicron lineages. Whether the increased immune escape of XBB* is sufficient to drive new infection waves appears to depend on the regional immune landscape as affected by the size and timing of previous Omicron waves, as well as the COVID-19 vaccination coverage.


BQ.1* is a sublineage of BA.5, which carries spike mutations in some key antigenic sites, including K444T and N460K. In addition to these mutations, the sublineage BQ.1.1 carries an additional spike mutation in a key antigenic site (i.e. R346T). As of epidemiological week 40 (3 to 9 October), from the sequences submitted to GISAID, BQ.1* has a prevalence of 6% and it has been detected in 65 countries. While there are no data on severity or immune escape from studies in humans, BQ.1* is showing a significant growth advantage over other circulating Omicron sublineages in many settings, including Europe and the US, and therefore warrants close monitoring. It is likely that these additional mutations have conferred an immune escape advantage over other circulating Omicron sublineages, and therefore a higher reinfection risk is a possibility that needs further investigation. At this time there is no epidemiologic data to suggest an increase in disease severity. The impact of the observed immunological changes on vaccine escape remains to be established. Based on currently available knowledge, protection by vaccines (both the index and the recently introduced bivalent vaccines) against infection may be reduced but no major impact on protection against severe disease is foreseen.

Overall summary

The Omicron variant of concern remains the dominant variant circulating globally, accounting for nearly all sequences reported to GISAID[1]. While we are looking at a vast genetic diversity of Omicron sublineages, they currently display similar clinical outcomes, but with differences in immune escape potential.

The potential impact of these variants is strongly influenced by the regional immune landscape. While reinfections have become an increasingly higher proportion of all infections, this is primarily seen in the background of non-Omicron primary infections. With waning immune response from initial waves of Omicron infection, and further evolution of Omicron variants, it is likely that reinfections may rise further.

The role of the TAG-VE is to alert WHO if a variant with a substantially different phenotype (e.g. a variant that can cause a more severe disease or lead to large epidemic waves causing increased burden to the healthcare system) is emerging and likely to pose a significant threat. Based on currently available evidence, the TAG-VE does not feel that the overall phenotype of XBB* and BQ.1* diverge sufficiently from each other, or from other Omicron sublineages with additional immune escape mutations, in terms of the necessary public health response, to warrant the designation of a new variant of concern and assignment of a new label, but the situation will be reassessed regularly. We note these two sublineages remain part of Omicron, which is a variant of concern with very high reinfection and vaccination breakthrough potential, and surges in new infections should be handled accordingly.

While so far there is no epidemiological evidence that these sublineages will be of substantially greater risk compared to other Omicron sublineages, we note that this assessment is based on data from sentinel nations and may not be fully generalizable to other settings. Wide-ranging, systematic laboratory-based efforts are urgently needed to make such determinations rapidly and with global interpretability.

WHO will continue to closely monitor the XBB* and BQ.1* lineages as part of Omicron and requests countries to continue to be vigilant, to monitor and report sequences, as well as to conduct independent and comparative analyses of the different Omicron sublineages.

The TAG-VE meets regularly and continues to assess the available data on the transmissibility, clinical severity, and immune escape potential of variants, including the potential impact on diagnostics, therapeutics, and the effectiveness of vaccines in preventing infection and/or severe disease.

[1] Weekly epidemiological update on COVID-19 - 26 October 2022 (

Dec. 29, 2021

Please see the attached E-book for:


“Investigation of a SARS-CoV-2 B.1.1.529 (Omicron) Variant Cluster — Nebraska, November–December 2021”

Link when live:

Dec. 27, 2021

CDC Updates and Shortens Recommended Isolation and Quarantine Period for General Population

Given what we currently know about COVID-19 and the Omicron variant, CDC is shortening the recommended time for isolation from 10 days for people with COVID-19 to 5 days, if asymptomatic, followed by 5 days of wearing a mask when around others. The change is motivated by science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after. Therefore, people who test positive should isolate for 5 days and, if asymptomatic at that time, they may leave isolation if they can continue to mask for 5 days to minimize the risk of infecting others.

Additionally, CDC is updating the recommended quarantine period for those exposed to COVID-19. For people who are unvaccinated or are more than six months out from their second mRNA dose (or more than 2 months after the J&J vaccine) and not yet boosted, CDC now recommends quarantine for 5 days followed by strict mask use for an additional 5 days. Alternatively, if a 5-day quarantine is not feasible, it is imperative that an exposed person wear a well-fitting mask at all times when around others for 10 days after exposure. Individuals who have received their booster shot do not need to quarantine following an exposure, but should wear a mask for 10 days after the exposure. For all those exposed, best practice would also include a test for SARS-CoV-2 at day 5 after exposure. If symptoms occur, individuals should immediately quarantine until a negative test confirms symptoms are not attributable to COVID-19.

Isolation relates to behavior after a confirmed infection. Isolation for 5 days followed by wearing a well-fitting mask will minimize the risk of spreading the virus to others. Quarantine refers to the time following exposure to the virus or close contact with someone known to have COVID-19. Both updates come as the Omicron variant continues to spread throughout the U.S. and reflects the current science on when and for how long a person is maximally infectious.

Data from South Africa and the United Kingdom demonstrate that vaccine effectiveness against infection for two doses of an mRNA vaccine is approximately 35%. A COVID-19 vaccine booster dose restores vaccine effectiveness against infection to 75%. COVID-19 vaccination decreases the risk of severe disease, hospitalization, and death from COVID-19. CDC strongly encourages COVID-19 vaccination for everyone 5 and older and boosters for everyone 16 and older. Vaccination is the best way to protect yourself and reduce the impact of COVID-19 on our communities.

The following is attributable to CDC Director, Dr. Rochelle Walensky:

“The Omicron variant is spreading quickly and has the potential to impact all facets of our society. CDC’s updated recommendations for isolation and quarantine balance what we know about the spread of the virus and the protection provided by vaccination and booster doses. These updates ensure people can safely continue their daily lives. Prevention is our best option: get vaccinated, get boosted, wear a mask in public indoor settings in areas of substantial and high community transmission, and take a test before you gather.”

Dec. 18, 2021

Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States

Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States (


  • On 26 November 2021, WHO designated the variant B.1.1.529 a variant of concern (VOC), on the basis of advice from WHO’s Technical Advisory Group on Virus Evolution. The variant has been given the name Omicron. Omicron variant is a highly divergent variant with a high number of mutations, including 26-32 in the spike protein, some of which are concerning and may be associated with humoral immune escape potential and higher transmissibility.
  • As of 16 December 2021, the Omicron variant has been identified in 89 countries across all six WHO regions. Current understanding of the Omicron variant will continue to evolve as more data becomes available.
  • The overall threat posed by Omicron largely depends on four key questions, including: (1) how transmissible the variant is; (2) how well vaccines and prior infection protect against infection, transmission, clinical disease and death; (3) how virulent the variant is compared to other variants; and (4) how populations understand these dynamics, perceive risk and follow control measures, including public health and social measures. Public health advice is based on current information and will be tailored as more evidence emerges around those key questions.
  • There is consistent evidence that Omicron has a substantial growth advantage over Delta. It is spreading significantly faster than the Delta variant in countries with documented community transmission, with a doubling time between 1.5–3 days. Omicron is spreading rapidly in countries with high levels of population immunity and it remains uncertain to what extent the observed rapid growth rate can be attributed to immune evasion, intrinsic increased transmissibility or a combination of both. However, given current available data, it is likely that Omicron will outpace Delta where community transmission occurs.
  • There are still limited data on the clinical severity of Omicron. More data are needed to understand the severity profile and how severity is impacted by vaccination and pre-existing immunity. Hospitalizations in the UK and South Africa continue to rise, and given rapidly increasing case counts, it is possible that many healthcare systems may become quickly overwhelmed.
  • Preliminary data suggest that there is a reduction in neutralizing titres against Omicron in those who have received a primary vaccination series or in those who have had prior SARS-CoV-2 infection , which may suggest a level of humoral immune evasion.
  • There are still limited available data, and no peer-reviewed evidence, on vaccine efficacy or effectiveness to date for Omicron. Preliminary findings of vaccine effectiveness studies (test-negative design) were obtained from South Africa and England, the United Kingdom. Available preliminary data to be interpreted with caution as the designs may be subject to selection bias and the results are based on relatively small numbers. Results from England indicate a significant reduction in vaccine effectiveness against symptomatic disease for Omicron compared to Delta after two vaccine doses of either Pfizer BioNTech-Comirnaty or AstraZeneca-Vaxzevria vaccines. There was, however,  higher effectiveness two weeks after a Pfizer BioNTech-Comirnaty booster, which was slightly lower or comparable to that against Delta. A non peer-reviewed study by South Africa researchers using private health insurance data reported reductions in vaccine effectiveness of the Pfizer BioNTech-Comirnaty vaccine against infection, and to a lesser degree against hospitalization.  Details about the methods or results were not available at the time of writing.
  • The diagnostic accuracy of routinely used PCR and antigen-based rapid diagnostic test (Ag-RDT) assays does not appear to be impacted by Omicron. Most Omicron variant sequences reported include a deletion in the S gene, which can cause an S gene target failure (SGTF) in some PCR assays. Though a minority of publicly-shared sequences lack this deletion, SGTF can be used as a proxy marker to screen for Omicron. However, confirmation should be obtained by sequencing, as this deletion can also be found in other VOCs (e.g. Alpha and subsets of Gamma and Delta) circulating at low frequencies globally.
  • Therapeutic interventions for the management of patients with severe or critical COVID-19 associated with the Omicron variant that target host responses (such as corticosteroids, and interleukin 6 receptor blockers) are expected to remain effective.  However, preliminary data from preprint publications suggest that some of the monoclonal antibodies developed against SARS-CoV-2 may have decreased neutralization against Omicron. Monoclonal antibodies will need to be tested individually for their antigen binding and virus neutralization, and these studies should be prioritized

To read the full document, click here: 

Enhancing Readiness for Omicron (B.1.1.529): Technical Brief and Priority Actions for Member States (

To view previous versions of this technical brief, please see the links below. The current version of all WHO information products and publications is authoritative.

28 November 2021 (updated 29 November with minor editorial corrections)

10 December 2021 (updated from the last version published on 28 November 2021)


Dec. 3, 2021




CDC is working with the Minnesota Department of Health and the New York City Department of Health and Mental Hygiene to investigate a confirmed case of COVID-19 caused by the Omicron variant. The individual, a resident of Minnesota, developed mild symptoms on November 22 and sought COVID-19 testing on November 24. The person has since recovered. The individual traveled to New York City and attended the Anime NYC 2021 convention at the Javits Center from November 19-21, 2021.


CDC recommends people follow COVID-19 prevention strategiesEveryone 5 years and older should get vaccinated and get a booster shot, if recommended. Get tested if you have symptoms and stay home if you are sick.


The following is attributable to CDC Director, Dr. Rochelle Walensky

“CDC has been actively monitoring and preparing for this variant. We have been working closely with Minnesota’s Department of Health and will continue to work diligently with other U.S. and global public health and industry partners as we learn more. CDC has expanded its capacity for genomic sequencing over the past nine months and we have more tools to fight the variant than we had at this time last year from vaccines to boosters to the prevention strategies that we know work including masking in indoor public settings, washing your hands frequently and physical distancing. These methods work to prevent the spread of COVID-19, no matter the genetic sequence.”