Israeli Prime Minister Naftali Bennett receives a third shot of coronavirus disease (COVID-19) vaccine as Israel launches booster shots for over 40 year-olds in Kfar Saba, Israel August 20, 2021. REUTERS/Ronen Zvulun

Israeli researchers have conducted a study among healthcare workers showing a significant decline in COVID-19 antibodies six months after they received the second shot of the Pfizer-BioNTech vaccine.

The study, conducted by researchers at Israel’s Sheba Medical Center, found a substantial waning of neutralizing antibody titers, especially among fully vaccinated men versus women, people over 65, and immunosuppressed individuals.

“We found that a significant and rapid decrease in humoral [immune] response to the BNT162b2 vaccine was observed within months after vaccination. The decrease in neutralizing antibody titers was brisk initially, in the period of up to 70 to 80 days, but slowed thereafter,” according to the study published Wednesday in the New England Journal of Medicine.

The study noted that many vaccines — for example those against measles, mumps, and rubella — have shown a 5-10% decrease in neutralizing antibody levels each year.

Conversely, the study also found that obese participants had a 31% increase in neutralizing antibody levels after the six-month testing period, as compared with non-overweight participants.

The research was based on a six-month prospective study involving 4,868 fully vaccinated healthcare workers who had their response tested monthly from December 19, 2020, to July 9, 2021, for the presence of anti-spike IgG and neutralizing antibodies.

“Overall, the accumulating evidence from our study shows that long-term humoral response and vaccine effectiveness in previously infected persons were superior to that in recipients of two doses of vaccine,” the authors wrote.

The findings suggest support for Israel’s booster shot campaign, which the country kicked off as it experienced a decline in immunity against COVID-19 some six months into high vaccination rates.

Israel has been a frontrunner in administering Pfizer/BioNtech booster shots, starting with members of at risk groups in July and, by the end of August, to anyone above the age of 12. About 37% of Israel’s 9.4 million population has received a booster shot.

“As this pandemic continues to evolve, the importance of determining immune correlates of protection after vaccination becomes clearer. Strategies to prolong host immunity need to be evaluated in order to protect the population against SARS-CoV-2 and its variants,” the study concluded.