How long does COVID-19 vaccine protection last?

How long does the protection against COVID-19 vaccines last?

Experts do not know yet because they are still studying vaccinated people to see when the protection may disappear. How well the vaccines work against new variants will also determine if, when and how often additional shots may be needed.

“We only have information as long as the vaccines have been tested,” said Deborah Fuller, a vaccine researcher at the University of Washington. “We need to examine the vaccinated population and start seeing at what point do people become vulnerable again to the virus?”

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So far, Pfizer’s ongoing trials show that the company’s two-dose vaccine will remain very effective for at least six months and probably longer. People who received Moderna’s vaccine also still had remarkable levels of antiviral antibodies six months after the second shot required.

Antibodies do not tell the whole story either. To fight uninvited guests like viruses, our immune system also has another line of defense called B and T cells, some of which can hang around long after antibody levels dwindle. If they encounter the same virus in the future, these battle-tested cells may jump into action faster.

Although they do not completely prevent disease, they can help blunt its severity. But exactly what role such “memory cells” may play with coronavirus – and for how long – is not yet known.

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While current COVID-19 vaccines are likely to last for at least about a year, they are unlikely to offer lifelong protection, as with measles, says Dr. Kathleen Neuzil, a vaccine expert at the University of Maryland.

“It will be somewhere in the middle of the very wide area,” she said.

Variants are another reason why we may need an extra shot.

The current vaccines are designed to work against a specific spike protein on the coronavirus, said Mehul Suthar of the Emory Vaccine Center. If the virus mutates enough over time, vaccines may need to be updated to increase their effectiveness.

So far, the vaccines appear to be protective against the remarkable variants that have emerged, albeit somewhat less so than those first detected in South Africa.

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If it turns out that we need a new shot, a single dose can extend the protection of the current shots or include vaccination for one or more varieties.

The need for follow-up shots will also partly depend on the success of the global vaccination campaign and the breakdown of the transmission of the virus and new variants.

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