Key points
SARS-CoV-2 continues to circulate and evolve with important genetic and antigenic evolution of the spike protein.
The objective of an update to COVID-19 vaccine antigen composition is to enhance vaccine-induced immune responses to circulating SARS-CoV-2 variants.
As the virus is expected to continue to evolve from JN.1, the TAG-CO-VAC advises the use of a monovalent JN.1 lineage as the antigen in future formulations of COVID-19 vaccines.
In accordance with WHO SAGE policy, vaccination programmes should continue to use any of the WHO emergency-use listed or prequalified COVID-19 vaccines and vaccination should not be delayed in anticipation of access to vaccines with an updated composition.
Evidence reviewed
The published and unpublished evidence reviewed by the TAG-CO-VAC included: (1) SARS-CoV-2 genetic evolution with support from the WHO Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE); (2) Antigenic characterization of previous and emerging SARS-CoV-2 variants using virus neutralization tests with animal antisera or human sera and further analysis of antigenic relationships using antigenic cartography; (3) Immunogenicity data on the breadth of neutralizing antibody responses elicited by currently approved vaccine antigens against circulating SARS-CoV-2 variants using animal and human sera, including modelling data; (4) Vaccine effectiveness estimates (VE) of currently approved vaccines during periods of circulation of XBB.1 and JN.1 lineages; (5) Preliminary immunogenicity data on immune responses following infection with circulating SARS-CoV-2 variants; and (6) Preliminary preclinical and clinical immunogenicity data on the performance of candidate vaccines with updated antigens shared confidentially by vaccine manufacturers with TAG-CO-VAC. Further details on the publicly available data reviewed by the TAG-CO-VAC can be found in the accompanying data annex. Unpublished and/or confidential data reviewed by the TAG-CO-VAC are not shown.
The objective of an update to COVID-19 vaccine antigen composition is to enhance vaccine-induced immune responses to circulating SARS-CoV-2 variants.
As the virus is expected to continue to evolve from JN.1, the TAG-CO-VAC advises the use of a monovalent JN.1 lineage as the antigen in future formulations of COVID-19 vaccines.
In accordance with WHO SAGE policy, vaccination programmes should continue to use any of the WHO emergency-use listed or prequalified COVID-19 vaccines and vaccination should not be delayed in anticipation of access to vaccines with an updated composition.
Evidence reviewed
The published and unpublished evidence reviewed by the TAG-CO-VAC included: (1) SARS-CoV-2 genetic evolution with support from the WHO Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE); (2) Antigenic characterization of previous and emerging SARS-CoV-2 variants using virus neutralization tests with animal antisera or human sera and further analysis of antigenic relationships using antigenic cartography; (3) Immunogenicity data on the breadth of neutralizing antibody responses elicited by currently approved vaccine antigens against circulating SARS-CoV-2 variants using animal and human sera, including modelling data; (4) Vaccine effectiveness estimates (VE) of currently approved vaccines during periods of circulation of XBB.1 and JN.1 lineages; (5) Preliminary immunogenicity data on immune responses following infection with circulating SARS-CoV-2 variants; and (6) Preliminary preclinical and clinical immunogenicity data on the performance of candidate vaccines with updated antigens shared confidentially by vaccine manufacturers with TAG-CO-VAC. Further details on the publicly available data reviewed by the TAG-CO-VAC can be found in the accompanying data annex. Unpublished and/or confidential data reviewed by the TAG-CO-VAC are not shown.
Summary of available evidence
- SARS-CoV-2 continues to circulate and evolve; there are genetic changes in important regions of the spike protein of SARS-CoV-2.
- As of April 2024, nearly all (>94%) SARS-CoV-2 genetic sequences in publicly available databases are derived from JN.1, and these variants continue to displace existing XBB lineage variants (e.g. EG.5). This displacement indicates greater fitness of JN.1 derived variants as compared to other circulating SARS-CoV-2 variants in the human population.
- Several JN.1 derived variants (e.g. JN.1.13.1, JN.1.11.1, KP.2) have independently evolved changes in the spike protein at epitopes involving amino acid residues 346 and/or 456. Substitutions at these amino acid residues have been identified in previous SARS-CoV-2 variants (e.g. R346T in BQ.1 and XBB; F456L in EG.5 and HK.3) and are within epitopes known to be targeted by neutralizing antibodies.
- Given the displacement of XBB lineage variants by JN.1 derived variants, it is likely that, in the near-term, circulating SARS-CoV-2 variants will be derived from JN.1.
- In immunologically naïve animal and human sera, XBB.1.5 and JN.1 are antigenically distinct SARS-CoV-2 variants. In non-naïve animals and humans, post-monovalent XBB.1.5 vaccination sera, with or without recent prior infection, neutralize XBB.1.5 and its derivatives including EG.5, HK.3, HV.1, as well as BA.2.86 and JN.1. However, neutralization titres against JN.1 in published and unpublished studies were typically lower (2-5-fold) than those against the homologous XBB.1.5 immunizing antigen. There are further reductions in cross neutralization of JN.1 variants with F456L and/or R346T substitutions.
- Secondary analysis of published immunogenicity data demonstrates that an additional vaccine dose with an updated vaccine antigen results in an average 40% increase in neutralizing antibodies to that variant as compared to vaccines with a previous vaccine antigen. Using statistical modeling, the predicted additional effectiveness of a vaccine dose with an updated vaccine antigen may be approximately 23-33% against severe disease as compared to a previous vaccine antigen and 11-25% against symptomatic disease.
As of April 2024, nearly all circulating SARS-CoV-2 variants reported in publicly available databases are JN.1 derived variants. As virus evolution is expected to continue from JN.1, future formulations of COVID-19 vaccines should aim to induce enhanced neutralizing antibody responses to JN.1 and its descendent lineages. One approach recommended by TAG-CO-VAC is the use of a monovalent JN.1 lineage (GenBank: PP298019, GISAID: EPI_ISL_18872762) antigen in vaccines.
The continued use of the current monovalent XBB.1.5 formulation will offer protection given the neutralizing antibody responses to early JN.1 descendent lineages, and the evidence from early rVE studies against JN.1. However, it is expected that the ability for XBB.1.5 vaccination to protect against symptomatic disease may be less robust as SARS-CoV-2 evolution continues from JN.1. Other formulations and/or platforms that achieve robust neutralizing antibody responses against currently circulating variants, particularly JN.1 descendent lineages, can also be considered.
In accordance with WHO SAGE policy, vaccination programmes should continue to use any of the WHO emergency-use listed or prequalified COVID-19 vaccines and vaccination should not be delayed in anticipation of access to vaccines with an updated composition. WHO stresses the importance of access to and equity in the use of all available COVID-19 vaccines.
Further data requirements and considerations
Given the limitations of the evidence upon which the recommendations above are derived and the anticipated continued evolution of the virus, the TAG-CO-VAC strongly encourages generation of data on immune responses and clinical endpoints (i.e. VE) on the performance of all currently approved COVID-19 vaccines against emerging SARS-CoV-2 variants, and candidate vaccines with an updated antigen over time.
As previously stated, the TAG-CO-VAC continues to encourage the further development of vaccines that may improve protection against infection and reduce transmission of SARS-CoV-2.
Website: International Conference on Infectious Diseases
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