Does frequently updating COVID-19 vaccines have any benefits? | Explained Premium
The Hindu
COVID-19 vaccines: A new study has found that updated vaccines improved neutralising antibody titres compared to non-updated formulations, but the matching problem persists
Researchers update the composition of influenza vaccines every six months to match the strains of the virus that are circulating in the wild, so that the shots may provide protective immunity against the flu. But despite their best efforts, researchers rarely perfectly match the strains loaded in the vaccine with the strains circulating by the time the vaccines reach the market.
The reason for this is the long gestation period – usually at least six months – between identifying the circulating strain and the development, manufacturing, and distribution of the vaccines. By the time the updated flu vaccine is available, the circulating strain may have drifted from the one contained in the vaccine, thanks to the high mutational rates of influenza viruses.
The ‘match’ between strains included in the vaccine and strains in circulation is the most important factor controlling the vaccine effectiveness (VE) of flu vaccines. The VE increases by more than 25% when there is a match with the circulating strains but can be as low as 10% in seasons when there is no match.
Another issue with flu vaccines is the durability of protection. According to a recent study, the VE declines by 7% for H3N2 to 11% for H1N1 viruses per month, and could vanish as soon as 90 days after vaccination.
There are some striking similarities between the influenza and COVID-19 vaccines. The VE of COVID-19 vaccines varies according to the disease’s progression as well as the circulating strains. With the advent of the highly mutated Omicron variant of SARS-CoV-2, the VE of COVID-19 vaccines has nose-dived.
According to one large study, COVID-19 vaccines had a VE of 52.8% against the Delta variant but only 16.4% against the Omicron. Another large review – of the findings of 78 studies on the VE of four COVID-19 vaccines before the advent of Omicron – concluded that VE against symptomatic disease waned by 20-30% by the sixth month of the primary series.
Thus, researchers worldwide rushed to revise COVID-19 vaccines that contained the ancestral strain to match the circulating strain of SARS-CoV-2, and thus remain clinically relevant.
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