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.
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.
In line with this approach, there are many options to consider:
- 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 needed to develop a modified or new vaccine;
- a multivalent vaccine containing antigens from different SARS-CoV-2 VOCs;
- a pan SARS-CoV-2 vaccine: a more sustainable long-term option that would effectively be variant-proof.
In the interim, the TAG-CO-VAC encourages COVID-19 vaccine manufacturers to generate and provide data on performance of current and Omicron-specific COVID-19 vaccines, including the breadth, magnitude, and durability of humoral and cell mediated immune responses to variants through monovalent and/or multivalent vaccines. These data will be considered in the context of the framework mentioned above to inform the TAG-CO-VAC decisions when changes to vaccine composition may be required. 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.
Addressing the challenge of continuing to ensure the production of the best possible vaccines in a timely manner requires a continuous exchange of information and collaboration between WHO and its expert groups, the TAG-CO-VAC, regulatory authorities, and COVID-19 vaccine manufacturers. WHO, on behalf of its Member States, is committed to facilitating this process.
This statement and its conclusions will be updated by the TAG-CO-VAC as data become available.