In September 2021, WHO established the Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC). This multidisciplinary group of 18 experts reviews and assesses the public health implications of emerging VOCs on the performance of COVID-19 vaccines and provides recommendations on COVID-19 vaccine composition.  The work of this group complements the work of the Technical Advisory Group on the Evolution of SARS-CoV-2 Virus (TAG-VE), the Strategic Advisory Group of Experts on Immunization (SAGE) and its Working Group on COVID-19 Vaccines, and the working groups of the WHO R&D Plan for Epidemics.
Since its emergence, the SARS-CoV-2 virus has continued to evolve and, to date, WHO has designated five variants as Variants of Concern of SARS-CoV-2, namely Alpha, Beta, Gamma, Delta and Omicron, due to their impact on transmission, disease severity or immune escape capacity. Although the Omicron variant is spreading rapidly worldwide, the evolution of SARS-CoV-2 is expected to continue and Omicron is unlikely to be the last VOC.
TAG-CO-VAC is developing a framework to analyze the evidence on emerging VOCs in the context of criteria that would trigger a recommendation to change the composition of the COVID-19 vaccine strain and will advise WHO on updated vaccine compositions as needed.
This framework considers global spread and transmissibility, clinical severity, genetic, antigenic and phenotypic characteristics of VOC, including immune escape capacity, and evaluations of vaccine efficacy.
Since WHO classified the Omicron variant as a VOC on November 26, 2021, the TAG-CO-VAC has met regularly to review the evidence on the characteristics of the Omicron variant. This statement reflects the current understanding of the implications of the appearance of the Omicron variant in current COVID-19 vaccines and provides the TAG-CO-VAC’s current perspective on vaccine options for the future.
Global public health goals of COVID-19 vaccines
With COVID-19 vaccines available, the current goal remains to reduce severe disease and death, as well as to protect healthcare systems. Vaccines that have received WHO emergency use listing, across several vaccine platforms, provide a high level of protection against severe disease and death caused by COVID.
In the case of the Omicron variant, the mutational profile and preliminary data indicate that vaccine efficacy will be reduced against symptomatic disease caused by the Omicron variant, but protection against severe disease is more likely to be retained. However, more data are needed on vaccine efficacy, particularly against hospitalization, severe disease, and death, including for each vaccine platform and various vaccine and product dosing regimens.
Consistent with SAGE and its COVID-19 Vaccines Working Group, TAG-CO-VAC therefore supports urgent and broad access to current COVID-19 vaccines for priority populations worldwide to protect against severe illness and death globally and, in the longer term, to mitigate the emergence and impact of new VOCs by reducing the burden of infection.
In practical terms, while some countries may recommend booster doses of vaccine, the immediate priority for the world is to accelerate access to primary vaccination, especially for groups at highest risk of developing severe disease.
Given the short- and medium-term supply of available vaccines, the need for equity in access to vaccines in all countries to achieve global public health goals, programmatic considerations including vaccine demand, and the evolution of the virus, a vaccination strategy based on repeated booster doses of the original vaccine composition is unlikely to be appropriate or sustainable.
Composition of current and future COVID-19 vaccines
TAG-CO-VAC believes that COVID-19 vaccines that have a high impact on preventing infection and transmission, in addition to preventing severe disease and death, are needed and should be developed. Until such vaccines become available, and as the SARS-CoV-2 virus evolves, the composition of current COVID-19 vaccines may need to be updated to ensure that COVID-19 vaccines continue to provide WHO-recommended levels of protection against COV infection and disease, including Omicron and future variants.
The TAG-CO-VAC will consider a change in vaccine composition
to ensure that the vaccines continue to meet the criteria set out in the WHO target product profile for COVID-19 vaccines, including protection against severe disease improving vaccine-induced protection.
in addition to protection against severe disease and death, be more effective in protecting against infection, thereby reducing community transmission and the need for stringent and wide-ranging health and social measures elicit broad, strong and long-lasting immune responses to reduce the need for successive booster doses.
According to this approach, there are many options to be considered
a monovalent vaccine that elicits an immune response against the predominant circulating variant(s), although this option faces the challenge of the rapid emergence of SARS-CoV-2 variants and the time required to develop a modified or new vaccine.
In the meantime, TAG-CO-VAC encourages COVID-19 vaccine manufacturers to generate and provide data on the performance of current and Omicron-specific COVID-19 vaccines, including the breadth, magnitude and durability of humoral and cell-mediated immune responses to variants via monovalent and/or multivalent vaccines.
These data will be considered in the context of the above framework to inform TAG-CO-VAC decisions when changes in vaccine composition are required. It would be important for vaccine manufacturers to take short-term steps in the development and testing of vaccines with predominantly circulating variants and to share these data with TAG-CO-VAC and other relevant WHO expert committees. Vaccine manufacturers are also encouraged to provide such data for any novel, broadly reactive SARS-CoV-2 vaccines that are developed.
The TAG-CO-VAC will continue to evaluate evidence on the predominant circulating VOC(s) concerning spread/transmissibility properties, clinical severity (virulence), genetic, antigenic and phenotypic characteristics of the VOC, including immune escape capacity, and evaluations of vaccine efficacy and impact, as well as information provided by manufacturers.
TAG-CO-VAC will then advise WHO on the composition of the COVID-19 vaccine strain, which could be developed as a monovalent vaccine with the predominant circulating variant or as a multivalent vaccine derived from different variants.
Meeting the challenge of continuing to ensure the production of the best possible vaccines promptly requires a continuous exchange of information and collaboration between WHO and its expert groups, TAG-CO-VAC, regulatory authorities and the manufacturers of the COVID-19 vaccine. WHO, on behalf of its Member States, is committed to facilitating this process.
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