Effectiveness of Pfizer COVID-19 vaccine drops significantly after 6 months: Israeli study

JERUSALEM, Nov. 17 (Xinhua) -- The effectiveness of the two-dose regimen of the Pfizer COVID-19 vaccine decreases significantly after about six months, said an Israeli study recently published in open access journal Nature Communications.

The study was co-conducted by the KI Research Institute in central Israel and KSM, the research and innovation institute of Israel's second-largest health maintenance organization Maccabi Healthcare Services (MHS).

Leveraging the centralized computerized database of MHS, the study assessed the correlation between time-from-vaccine and incidence of breakthrough infection, or infection after vaccination, in a follow-up period from June 1 to July 27.

Of 1,395,134 MHS members aged above 16 who received the second dose of the Pfizer vaccine between January and April, 1,352,444 were eligible for the study.

During the follow-up period, 1,911 cases of breakthrough infection were recorded, 1,151 of them vaccinated between January and February and 760 vaccinated between March and April, said the study.

The risk of infection among individuals vaccinated between January and February was more than 51 percent higher than those vaccinated between March and April, it said.

When stratifying the results by age, the study found a similar trend across all age groups.

Besides, individuals vaccinated in January had a 2.26-fold increased risk for breakthrough infection compared to those vaccinated in April, said the study.

"Our results correspond to recent publications that demonstrate a significant decline in antibody levels and immune systems compounds over time following the second dose of vaccination," it said.