How long does protection from COVID-19 vaccines last?
Experts don't know yet because they're still studying vaccinated people to see when protection might wear off. How well the vaccines work against emerging variants may also determine if, when and how often additional shots could possibly be needed.
“We only have information for provided that the vaccines have already been studied," said Deborah Fuller, a vaccine researcher at the University of Washington. “We must study the vaccinated population and learn to see, at what point do people become vulnerable again to the virus?”
Up to now, Pfizer's ongoing trial indicates the company's two-dose vaccine remains impressive for at least half a year, and likely longer. Individuals who got Moderna’s vaccine also still had notable degrees of virus-fighting antibodies six months following the second required shot.
Antibodies also don't tell the whole story. To fight off intruders like viruses, our immune systems also have another line of defense called B and T cells, some of which can hang around long after antibody levels dwindle. If indeed they face the same virus later on, those battle-tested cells may potentially spring into action quicker.
Even if indeed they don't prevent illness entirely, they may help blunt its severity. But precisely what role such “memory” cells might play with the coronavirus -- and for how long -- isn’t yet known.
As the current COVID-19 vaccines will likely last for at least about a year, they probably won’t offer lifelong protection, much like measles shots, said Dr. Kathleen Neuzil, a vaccine expert at the University of Maryland.
“It’s likely to be somewhere in the center of that very wide range,” she said.
Variants are another reason we may need yet another shot.
The current vaccines are created to work against a particular spike protein on the coronavirus, said Mehul Suthar of the Emory Vaccine Center. If the virus mutates enough as time passes, vaccines may need to be updated to improve their effectiveness.
Up to now, the vaccines appear protective against the notable variants that contain emerged, though somewhat less etc the main one first detected in South Africa.
If it turns out we are in need of another shot, an individual dose could extend protection of the current shots or contain vaccination for one or more variants.
The need for follow-up shots may also depend partly on the success of the vaccination push globally, and tamping down transmission of the virus and emerging variants.