Some Vaccines Last a Lifetime. Here’s Why Covid-19 Shots Don’t.

Researchers have calculated a key number—the threshold of protection—for other vaccines. Covid-19’s is still a mystery.

Recent studies have shown that the effectiveness of Covid-19 vaccines is decreasing, though experts say the shots still work well. WSJ explains what the numbers mean and why they don’t tell the full story. Photo illustration: Jacob Reynolds/WSJ
By

Jo Craven McGinty

Why don’t Covid-19 vaccinations last longer?

Measles shots are good for life, chickenpox immunizations protect for 10 to 20 years, and tetanus jabs last a decade or more. But U.S. officials are weighing whether to authorize Covid-19 boosters for vaccinated adults as soon as six months after the initial inoculation.

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