In two new studies from Israel and Qatar, researchers found that the immunity offered by two doses of Pfizer’s coronavirus vaccine drops off after about two months.
But the protection against severe disease, hospitalization and death holds strong.
The findings suggest even fully vaccinated people need to continue to guard against COVID-19 infection.
In the first study, researchers found that antibody levels among 4,800 health care workers fell rapidly within months after two doses of the Pfizer vaccine.
This is true especially among men, among persons 65 years of age or older, and among persons with immunosuppression.
That team also found that that immunity lasts longer in people who are vaccinated after natural COVID-19 infection.
In the second study, researchers found that the protection against infection builds rapidly after the first dose, peaks in the first month after the second dose, and then gradually wanes in subsequent months.
The waning appears to accelerate after the fourth month, to reach a low level of approximately 20% in subsequent months.
However, the researchers also found that protection against hospitalization and death remained above 90%.
They say the vaccine’s weakening protection may be due to people’s behavior. Vaccinated persons presumably have a higher rate of social contact than unvaccinated persons and may also have lower adherence to safety measures.
This behavior could reduce the real-world effectiveness of the vaccine as compared with its biological effectiveness, possibly explaining the waning of protection.
The study findings are published in the New England Journal of Medicine. One author of the study is Laith Abu-Raddad.
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