Immunity weakens faster in men than women after second Pfizer shot: Study

The immunity against coronavirus disease (Covid-19) weakens faster in men than women after the second dose of the Pfizer-BioNTech vaccine, according to a new study released Wednesday. Pfizer vaccine has shown the efficacy of 94-95% in preventing symptomatic Covid-19 seven days after the second shot of the two-dose regimen, however, the data on the durability of vaccines are still limited.

The incidence of symptomatic Covid-19 has been increasing in Israel despite high vaccine coverage and effectiveness, prompting researchers to study whether it is due to waning immunity after the receipt of two doses of Pfizer's BNT162b2 vaccine. More than 4,800 healthcare professionals participated in the 6-month longitudinal prospective study.

The study, published in the New England Journal of Medicine, found that the neutralising antibody level substantially decreased six months after the second dose of Pfizer vaccine, especially among participants 65 years of age or older. It also suggested that neutralizing antibody concentrations among persons 65 years of age or older were at a lower level than participants between 18 to 45 years of age.

The neutralizing antibody concentrations were lower in men 65 years of age or older as than women in the same age group. The neutralizing antibody titers declined briskly in the period of up to 80 days after the second dose of the Covid-19 vaccine, but slowed afterwards, according to the study.

"Particularly vulnerable populations with lower neutralizing titers were older men and participants with immunosuppression," the authors wrote.

While obesity is associated with severe Covid-19, the authors said it is still unclear whether vaccinated obese persons are at higher or lower risk for breakthrough infection. 

The United States has recommended a booster dose of Pfizer vaccine for people aged 65 and above and other vulnerable groups.