Consider updating COVID-19 vaccine composition to include omicron: WHO to authorities

The only other precedent we have for updating vaccines regularly based on the circulating strain is for flu. But the comparison may not be fair

By Taran Deol
Published: Monday 17 April 2023
Consider updating COVID vaccine composition to include omicron: WHO to authorities
Tailoring vaccines to keep up with evolving SARS-CoV-2 strains is the easiest to do for mRNA-based vaccines. Photo: iStock
Photo: iStock Tailoring vaccines to keep up with evolving SARS-CoV-2 strains is the easiest to do for mRNA-based vaccines. Photo: iStock Photo: iStock

The first dose of a clinically approved vaccine against SARS-CoV-2, developed by Pfizer, was administered on December 8, 2020. Since then, the roadmap for immunisation against COVID-19 has evolved several times, attempting to keep up with the mutating virus. 

The Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC), in its most recent meeting held March 16-17, discussed two key objectives: Review the evidence on the performance of updated COVID-19 vaccines that incorporate descendent lineages of Omicron as a booster dose; and establish timelines for COVID-19 vaccine composition recommendations in 2023.

The report, published by the World Health Organization (WHO) April 14, noted that while index virus-based vaccines continue to provide protection against severe disease and death, their effectiveness in protecting against symptomatic infection has been waning. 

Keeping this in mind, the report made recommendations to update existing vaccines to try and bridge the “antigenic distance” in the backdrop of “uncertainties of further viral evolution”. The suggestion seemed mild because the body simply “advised vaccine manufacturers and regulatory authorities to consider an update of vaccine antigen composition by including Omicron, as the most antigenically distinct SARS-CoV-2 variant thus far, for administration as a booster dose.” 

While the report acknowledged that variant-specific boosters targeting BA.1 and BA.4 / BA.5 confer better protection than using the original vaccine, it also shed light on the immune imprinting phenomenon, where “immune memory recall biases the immune response towards previously encountered antigen”. 

However, limited data based on epidemiological studies plagues our understanding of the clinical impact of immune imprinting. The global health body remains steadfast in its view that “achieving broader cross-reactive vaccine-induced immune responses remains prudent in the context of continued SARS-CoV-2 evolution.” 

In conclusion, the report outlined the aims of the upcoming meetings of TAG-CO-VAC; whether the index virus should be a part of future vaccination updates. 

Tailoring vaccines to keep up with the evolving SARS-CoV-2 is a practice that began last July, when sub-lineages of Omicron had begun causing waves across different geographies. It is the easiest to do so for mRNA-based vaccines. 

Essentially, the existing antigen is replaced with a new antigen, for which two critical ingredients are needed: Genetic sequence of the spike protein from a new variant of concern and a DNA template to build the mRNA, Down To Earth (DTE) had earlier reported

Experts estimated that it will take 52 days for manufacturers to carry out preclinical tests and another 100 days for human trials. Updating viral vector and protein-based vaccines is a more tedious and long-drawn process. 

The only other precedent we have for updating vaccines regularly based on what strain is circulating is with flu. But that comparison is not entirely fair, since we understand the flu virus much better than SARS-CoV-2. 

Read more: How do you make a universal flu vaccine? A microbiologist explains

“The value in developing new variant vaccines is always mitigated against the time taken to find a new variant, figure out if it’s an important one, [and then] develop, modify the vaccine, check it’s worked and approve,” Paul Hunter, professor of medicine at the University of East Anglia, was quoted as saying in an article for journal The BMJ.

Three risk groups have been identified based on risk of severe disease and death, complimented with our understanding of vaccine performance, cost-effectiveness, programmatic factors and community acceptance; high, medium and low, according to the latest set of recommendations made by the Strategic Advisory Group of Experts on Immunization (SAGE) March 28, 2023.

For the high priority group — older adults; younger adults with significant comorbidities (diabetes, heart disease); people with immunocompromising conditions (those living with HIV, transplant recipients), including children aged six months and older; pregnant persons; and frontline health workers — SAGE recommended an additional booster shot 6-12 months after the last dose. 

For the medium priority group —  healthy adults below 60 years of age and children and adolescents with comorbidities — SAGE recommended primary vaccination and one booster dose. 

For the low priority group, SAGE suggests making vaccination decisions based on “contextual factors, such as the disease burden, cost effectiveness, and other health or programmatic priorities and opportunity costs”.

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