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 Variants of Concern (VOCs) on the performance of COVID-19 vaccines and provides recommendations on COVID-19 vaccine composition.
The work of this group complements that of the Technical Advisory Group on SARS-CoV-2 Virus Evolution (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 Blueprint for Epidemics.
The 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 COVID-19 vaccine strain composition and will advise WHO on updated vaccine compositions, as required. This framework considers the global spread and transmissibility, clinical severity, genetic, antigenic and phenotypic characteristics of the VOC, including capacity for immune escape and assessments of vaccine effectiveness.
With available COVID-19 vaccines, the current focus remains on reducing severe disease and death, as well as protecting health 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 VOCs. For the Omicron variant, the mutational profile and preliminary data indicate that vaccine effectiveness will be reduced against symptomatic disease caused by the Omicron variant, but protection against severe disease is more likely to be preserved. However, more data on vaccine effectiveness, particularly against hospitalization, severe disease, and death are needed, including for each vaccine platform and for various vaccine dosing and product regimens.
In alignment with SAGE and its Working Group on COVID-19 Vaccines, the TAG-CO-VAC therefore supports urgent and broad access to current COVID-19 vaccines for priority populations worldwide to provide protection against severe disease 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 accelerating access to the primary vaccination, particularly for groups at greater risk of developing severe disease.
Composition of current and future COVID-19 vaccines
The TAG-CO-VAC considers that COVID-19 vaccines that have high impact on prevention of infection and transmission, in addition to the prevention of severe disease and death, are needed and should be developed. Until such vaccines are 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 infection and disease by VOCs, including Omicron and future variants.
The TAG-CO-VAC will consider a change in vaccine composition:
- to ensure that vaccines continue to meet the criteria established in WHO’s Target Product Profile for COVID-19 vaccines, including protection against severe disease
- to improve vaccine-induced protection.
To that aim, COVID-19 vaccines need to:
- be based on strains that are genetically and antigenically close to the circulating SARS-CoV-2 variant(s);
- in addition to protection against severe disease and death, be more effective in protection against infection thus lowering community transmission and the need for stringent and broad-reaching public health and social measures;
- elicit immune responses that are broad, strong, and long-lasting in order to reduce the need for successive booster doses.
It would be important for vaccine manufacturers to take steps in the short-term for the development and testing of vaccines with predominant circulating variants and to share these data with the TAG-CO-VAC and other relevant WHO expert committees. Vaccine manufacturers are also encouraged to provide such data for any novel and broadly reactive SARS-CoV-2 vaccines that are developed.
The TAG-CO-VAC will continue to assess evidence on the predominant circulating VOC(s) with respect to properties of spread/transmissibility, clinical severity (virulence), genetic, antigenic and phenotypic characteristics of the VOC, including capacity for immune escape and assessments of vaccine effectiveness and impact, and information provided by manufacturers. The TAG-CO-VAC will then advise WHO on COVID-19 vaccine strain composition, which could potentially be developed either as a monovalent vaccine with the predominant circulating variant or a multivalent vaccine derived from different variants.
Link to the WHO Interim Statement: