The Future of SARS-CoV-2 Vaccination — Lessons from Influenza

By Arnold S. Monto, M.D.

“After a period of falling Covid-19 illness rates, the recent spread of the delta variant of SARS CoV-2 was a major disappointment and necessitated a reexamination of some previous assumptions.  This reconsideration may, at least in part, be a correction to overly optimistic views of what highly effective SARS-CoV-2 vaccines could accomplish. Some observers had hoped the vaccines could eliminate transmission of the virus, the ultimate goal of reaching herd immunity. 1 A more likely picture of our future with this virus comes into focus if we examine the well-known infection patterns of another respiratory virus, influenza, both in and outside pandemics. That experience can help us reset expectations and modify goals for dealing with SARS-CoV-2 as it further adapts to a global spread.

Early results from the clinical trials and observational studies of mRNA vaccines against SARS-CoV-2 indicated that not only were they are highly effective at preventing symptomatic infection, but they were also effective in preventing asymptomatic infection and therefore transmission. 2 The basic criterion used for emergency use authorization by the Food and Drug Administration was a standard one: prevention of laboratory-confirmed clinical infection meeting a case definition. The effect on asymptomatic infections was a welcome surprise because it has been thought that most vaccines for respiratory illnesses, including influenza, are “leaky” — that is, they allow some degree of asymptomatic infection and are better at preventing symptomatic infection.”

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The Future of SARS-CoV-2