People vaccinated with two shots of the Pfizer coronavirus vaccine in January and February had a 51% increased chance of contracting the virus in July compared to those who were vaccinated in March or April, a new Israeli study published in Nature Communications has shown.
The team of researchers from KI Institute worked with doctors from KSM Research and Innovation and used data provided by Maccabi Health Services to conduct a retrospective cohort study comparing the incidence rates of breakthrough infections and COVID-19-related hospitalizations between people vaccinated toward the beginning of the country’s campaign (January and February) and those vaccinated toward the later stages (March and April). The study included more than 1.3 million records.
As noted, the risk of infection was significantly higher for people the earlier they were vaccinated, with an additional trend for high risk of hospitalization. The results, the researchers said, are consistent with other studies on the subject that show a decline in antibody levels and immune system compounds after four to six months.
Moreover, people’s ages had no effect on the vaccine’s waning, meaning that the vaccine waned for everyone and not just older people.
"The vaccine's effectiveness wanes equally for everybody, according to the study," Dr. Barak Mizrahi, a researcher in computational health for KI Institute who led the study, said.
Israel set a policy to administer a third shot to all individuals over the age of 12, in contrast to many other countries and the recommendation of the World Health Organization only to give the third jab to people at the highest risk of contracting the virus or developing serious disease.
More than four million Israelis have taken a booster shot. The results were that the infection rate dropped significantly.
Mizrahi explained that the vaccine waned more the further one got away from the original second dose, meaning that people vaccinated in January were more at risk of contracting corona than people vaccinated in February and so forth.
The study was done as the Delta variant was burning across the country and many believed that the variant may be the cause of increased infection in Israel. Mizrahi said the study shows that the variant was likely less of a factor than assumed – though this is still not confirmed.
Will the third dose last longer?
Mizrahi said that it is difficult to tell at this stage. Very preliminary data has started to be collected in various studies that shows antibodies are waning after the third shot, too. However, he said that the level of antibodies is not the only factor when it comes to immunity. Officials will need to watch and see if infections start going up and then set vaccination policy accordingly, Mizrahi said.
“I don’t think it will take us that long to know,” he concluded.