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The COVID vaccine's technology could finally fix the unreliable flu shot

An mRNA flu vaccine that updates close to season has finally been approved. Its speed means nothing until officials move a decades-old strain deadline

Eileen T. Meslar / Chicago Tribune / Tribune News Service via Getty Images

Americans have gotten a flu shot almost every fall for decades and watched it work only about half the time — and in the worst seasons far less — because manufacturers must lock in the vaccine's formula months before anyone knows which virus will actually spread.

In most recent seasons, the shot has cut the population's risk of a medically attended flu case by somewhere between 30 and 50%, but in a badly mismatched year, that figure can fall to as low as 19%, according to the Center for Disease Control and Prevention. When the strains turn out to be the ones that spread, effectiveness lands near the top of that range, but when the circulating virus differs from the one in the vial, it drops toward the bottom.

The guessing game starts each February, when the World Health Organization names the strains it expects to circulate. Manufacturers then spend roughly six to nine months growing viruses in hundreds of........

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