Pfizer Vaccine Effectiveness Drops Sharply Two Months After Vaccination

The Pfizer logo of the American pharmaceutical company reflected in the droplet of liquid at the tip of the syringe. [Image source=Yonhap News]

[Asia Economy Reporter Hwang Sumi] A study has found that the infection prevention effect of the Pfizer COVID-19 vaccine may be shorter than six months.

On the 6th (local time), CNN cited a study published in the latest issue of the New England Journal of Medicine (NEJM), a U.S. medical journal, reporting that the immune effect rapidly decreases two months after completing two doses of the Pfizer vaccine.

According to NEJM, a study was conducted on about 4,800 healthcare workers in Israel and Qatar. The study found that antibody levels sharply dropped two months after vaccination.

The researchers reported that immunity rapidly increased after the first dose, peaked one month after the second dose, but then began to decline.

This trend was especially pronounced in men aged 65 and older and in immunocompromised individuals. Additionally, those who were infected with COVID-19 and then vaccinated showed stronger antibody formation compared to those who were only vaccinated.

Dr. Gili Regev-Yochay, who led the study, said regarding the results, "The decline in immunity accelerated after four months post-vaccination, with antibody levels dropping to about 20%. However, the effectiveness in preventing hospitalization and death remained high at around 90%."

Regarding the reason for the decrease in immune effect, she speculated, "Vaccinated people may have more social contacts and follow safety guidelines less strictly than unvaccinated people," adding, "(This increased activity) could explain why the vaccine's effectiveness decreases more due to behavioral factors than biological effects."

Meanwhile, Pfizer had previously acknowledged that immune effectiveness begins to decline a few months after the second dose. The company also received approval from the U.S. Food and Drug Administration (FDA) for a third booster shot for those who are six months past their vaccination completion.