The studies, from Israel and Qatar, published in the New England Journal of Medicine, support arguments that even fully vaccinated people need to maintain precautions against infection.
“We conducted this prospective longitudinal cohort study with health workers from Sheba Medical Center, a large tertiary medical center in Israel,” wrote Dr. Gili Regev-Yochay and colleagues from Sheba.
The researchers noted that the levels of so-called neutralizing antibodies (the first line of defense of the immune system against infection) correlate with protection against infection, but for this study they only studied the levels of antibodies.
“Published work on many vaccines, such as those against measles, mumps, and rubella, has shown a small decrease each year from 5 to 10% in neutralizing antibody levels,” they wrote. “We found that a significant and rapid decrease in the humoral response to the BNT162b2 vaccine was observed a few months after vaccination.”
The study also indicated that the immunity of people who get vaccinated after a natural Covid-19 infection lasts longer. It is especially strong for people who recovered from the infection and then were vaccinated. “Overall, the cumulative evidence from our study and others shows that the long-term humoral response and vaccine efficacy in previously infected people were superior to those of two-dose vaccine recipients,” they wrote.
“Protection against BNT162b2-induced infection develops rapidly after the first dose, peaks in the first month after the second dose, and then gradually decreases in subsequent months,” wrote Laill Abu-Raddad of Weill Cornell Medicine-Qatar and colleagues. “The decline appears to be accelerating after the fourth month, to a low of approximately 20% in the following months,” they added.
However, protection against hospitalization and death remained above 90%, they said.
Declining protection can lead to behavior, they noted. “Vaccinated people presumably have a higher social contact rate than unvaccinated people and may also have less adherence to security measures,” they wrote. “This behavior could reduce the real-world efficacy of the vaccine compared to its biological efficacy, possibly explaining the decrease in protection.”
But it is a sign that countries should prepare for new Covid-19 uploads. “These results suggest that a large proportion of the vaccinated population could lose their protection against infection in the coming months, perhaps increasing the potential for new epidemic waves,” they wrote.
Pfizer has argued that the immunity of the first two doses of the vaccine begins to disappear after a few months. Last month, Pfizer obtained authorization 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 driven its entire population and now says it will require people to have a third shot to be considered fully vaccinated.
In the United States, more than 6 million people have received a third dose of vaccine and the average rate of booster vaccines is higher than the rate of people vaccinated for the first time, according to CDC data.
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