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- Two recent studies found that Pfizer's immunity protection diminishes rapidly a few months after a person has their second dose.
- However, one study noted that the vaccine's protection against death and hospitalization still remained as high as 96%.
- The studies affirm Pfizer's earlier comments that its vaccines may not defend against COVID-19 infection as effectively over time.
COVID-19 immunity protection from two doses of the Pfizer vaccine starts dwindling after about two month, still, the shots remain effective in guarding against hospitalization and death, according to a pair of studies published in the New England Journal of Medicine on Wednesday.
The new findings affirm what Pfizer, Moderna, and the Centers for Disease Control and Prevention have indicated in recent weeks – that the vaccines' ability to protect the body from coronavirus infection may wane over time. Last month, the Food and Drug Administration authorized Pfizer booster shots for older or more vulnerable people.
In the first study, researchers from Qatar found that Pfizer's immunity protection drops to as low as 20% just four months after a person receives their second dose. They based their report on observations of infections among Qatar's over 900,000 vaccinated people.
The researchers found that Pfizer's protection against infection was "negligible" shortly after the first dose, but jumps to 36.8% three weeks later. When people receive their second dose, immunity protection increases to 77.5% after about a month.
But once that month is over, Pfizer's immunity effectiveness declines steadily, hovering at around 20% after the four-month mark, per the researchers.
"These findings suggest that a large proportion of the vaccinated population could lose its protection against infection in the coming months, perhaps increasing the potential for new epidemic waves," wrote the report.
Still, Pfizer's protection against hospitalization and death remained "robust" at 90% or higher for six months after the second dose, it said. The report also noted that its findings may not apply well to countries with older populations, since Qatar's population is relatively young with only 9% of its people being 50 or older.
The other study, conducted in Israel, looked at 4,868 healthcare workers. It reported that people have substantially decreased COVID-19 antibodies just six months after receiving their second dose of Pfizer's vaccine.
The drop is especially prominent among men, the elderly above 65, and those with weakened immune systems.
In comparison, vaccines for other conditions such as mumps, measles, and rubella only show small decreases of about 5% to 10% each year in neutralizing antibody levels, wrote the researchers.
They also noted that they observed higher antibody counts in obese participants who have a body mass index of 30 or above.
"Yet, it is still unclear whether vaccinated obese persons are at higher or lower risk for breakthrough infection and whether the relatively high humoral response to the vaccine is protective," the report stated.