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The studies, from Israel and Qatar and published in the New England Journal of Medicine, support arguments that even fully vaccinated people should maintain precautions against infection.
“We conducted this prospective longitudinal cohort study involving healthcare workers at Sheba Medical Center, a large tertiary medical center in Israel,” wrote Dr. Gili Regev-Yochay and colleagues from Sheba.
The researchers noted that levels of so-called neutralizing antibodies – the immune system’s first line of defense against infection – correlated with protection against infection, but for this study, they only looked at levels of antibodies.
“Published work on many vaccines, such as those against measles, mumps and rubella, has shown a small decrease of 5-10% each year in neutralizing antibody levels,” they wrote. “We found that a significant and rapid decrease in the humoral response to the BNT162b2 vaccine was observed in the months following vaccination.”
The study also indicated that the immunity of people who get vaccinated after a natural infection with Covid-19 lasts longer. This is especially strong for people who have recovered from the infection and who have subsequently been vaccinated as well. “Overall, the accumulated evidence from our study and others shows that the long-term humoral response and vaccine efficacy in previously infected individuals was superior to that of recipients of two doses of the vaccine,” said they wrote.
“Protection against infection induced by BNT162b2 accumulates rapidly after the first dose, peaks in the first month after the second dose, then gradually wanes over the following months,” wrote Laith Abu-Raddad of Weill Cornell Medicine-Qatar and colleagues. “The decline seems to accelerate after the fourth month, reaching a low level of around 20% in the following months,” they added.
Nonetheless, protection against hospitalization and death remained above 90%, they said.
Decreasing protection may involve behavior, they noted. “Vaccinated people likely have a higher rate of social contact than unvaccinated people and may also have less adherence to safety measures,” they wrote. “This behavior could reduce the actual efficacy of the vaccine relative to its biological efficacy, possibly explaining the decline in protection.”
But it is a signal that countries must prepare for further outbreaks of Covid-19. “These results suggest that a large portion of the vaccinated population could lose their protection against infection in the months to come, possibly increasing the potential for further epidemic waves,” they wrote.
Pfizer has argued that the immunity of the first two doses of its vaccine begins to wane after a few months. Last month, Pfizer got clearance from the U.S. Food and Drug Administration for booster doses of its vaccine for about six months after people finished their first two doses.
Israel has increased its entire population and now says it will require people to have a third injection to be considered fully immunized.
In the United States, more than 6 million people have received a third dose of the vaccine and the average rate of boosters is higher than the rate of people getting their first shot, according to CDC data.
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