In June 2022, the TAG-CO-VAC released an interim statement noting that index virus-based vaccines continue to provide high levels of protection against severe disease caused by all variants of concern (VOCs) of SARS-CoV-2. including Omicron. However, given the antigenic distance and uncertainties of further viral evolution, the TAG-CO-VAC recognized that the effectiveness of virus index-based vaccines was likely to reduce over time. Therefore, the TAG-CO-VAC advised vaccine manufacturers and regulatory authorities to consider updating the vaccine’s antigen composition to include Omicron, as the most antigenically distinct SARS-CoV-2 variant to date. time, for administration as a booster dose. Multiple vaccine manufacturers have developed COVID-19 vaccines with an updated antigenic composition; this includes several mRNA-based bivalent vaccines containing earlier Omicron descendant lineages, in addition to the index virus (i.e., index virus + BA.1 or BA.4/5), which have been cleared for emergency use by regulatory authorities .
On March 16 and 17, 2023, the TAG-CO-VAC met again in Muscat, Oman. The purpose of the meeting was twofold: to review the evidence on the performance of updated COVID-19 vaccines that incorporate Omicron-descendant lineages as a booster dose; and set deadlines for COVID-19 vaccine composition recommendations in 2023.
Evidence reviewed by the TAG-CO-VAC to assess the performance of updated COVID-19 vaccines that incorporated lineages descended from Omicron included: (1) published observational epidemiological studies of absolute and relative vaccine effectiveness estimates from BA. 1- or BA .mRNA bivalent vaccines containing 4/5 used as booster doses against symptomatic and severe diseases; (2) Laboratory data on the magnitude and amplitude of cross-reactive immune responses against circulating and earlier SARS-CoV-2 variants induced by BA.1 or BA.4/5-containing mRNA vaccines, compared to the index virus -based vaccines, used as booster doses; and (3) laboratory studies and observational data on immune memory responses to assess the impact of repeated antigen challenge on vaccine-induced immunity and protection. More details on the evidence reviewed by the TAG-CO-VAC can be found in the attached document. exhibit.
Based on the review of the data described above, the TAG-CO-VAC concludes:
- Booster doses of index virus-based vaccines continue to provide high levels of protection against severe disease and death caused by all variants of SARS-CoV-2, including contemporary lineages descended from Omicron.
- Protection against severe disease and symptomatic infections induced by index virus-based vaccines and mRNA bivalent vaccines containing BA.1 or BA.4/5 decreases with time. However, protection against severe disease is maintained longer than protection against symptomatic infection.
- Compared with index virus-based vaccines, booster doses of BA.1- or BA.4/5-containing mRNA bivalent vaccines may modestly increase vaccine efficacy against symptomatic disease, while the small amount of studies evaluating serious outcomes show similar estimates for the vaccine. effectiveness.
- Bivalent mRNA vaccines containing BA.1 and BA.4/5 enhance the magnitude and elicit a greater amplitude of cross-reactive immune responses to SARS-CoV-2 variants when used as a booster dose, compared with the index virus. based vaccines
- BA.4/5-containing bivalent mRNA vaccines induced higher neutralizing antibody titers against recent Omicron lineages (BQ.1, XBB.1) compared to BA.1-containing bivalent mRNA vaccines, when were used as a booster dose.
- There is in vitro Evidence demonstrating that immune imprinting, also known as original antigenic sin, a phenomenon in which immune memory recall biases the immune response toward a previously encountered antigen, occurs with repeated exposure to the same antigen. However the clinical impact of immune imprinting in observational epidemiological studies to date is unclear, due to limited data and the potential for bias.
- As previously recommended by the TAG-CO-VAC in its statement published in June 2022Achieving broader cross-reactive vaccine-induced immune responses remains prudent in the context of the continuing evolution of SARS-CoV-2.
- At upcoming TAG-CO-VAC meetings, the antigen composition of the vaccine will be considered, including an assessment of whether the index virus is warranted for inclusion in future vaccine formulations. The TAG-CO-VAC will issue further recommendations on any updates after its next meeting in May 2023 (see below).
- For any vaccine product with an up-to-date antigenic composition, it is imperative that equitable global access be ensured.
- TAG-CO-VAC continues to encourage further development of vaccines that enhance mucosal immunity because they may improve protection against SARS-CoV-2 infection and transmission.
The role of the TAG-CO-VAC is to recommend whether updates to the vaccine composition are needed to continue to safely provide protection against SARS-CoV-2 variants; while recommendations on vaccination policies are issued by the Strategic Advisory Group of Experts on Immunization (SAGE); the latest SAGE recommendations on COVID-19 boosters can be found here.
The TAG-CO-VAC will continue to meet to assess the evidence to inform updates to the antigen composition of the COVID-19 vaccine. To this end, the TAG-CO-VAC plans to meet again twice in 2023: once in May 2023 and again approximately 6 months later. At each meeting, the genetic and antigenic evolution of SARS-CoV-2 variants, the performance of vaccine products against circulating SARS-CoV-2 variants, and the implications for the antigen composition of the COVID-19 vaccine will be evaluated. 19. Based on this evaluation, recommendations will be issued to maintain the current composition of the vaccine or to consider updates. This frequency of evidence review by the TAG-CO-VAC has been proposed given the kinetics of vaccine-derived immunity and the need for continuous monitoring of the evolution of SARS-CoV-2, and will be adjusted if necessary. necessary and as needed.
—————————————————-
Source link