Healthcare workers previously infected with the SARS-CoV-2 coronavirus had a strong immune response to one dose of the Pfizer/BioNTech Covid19 vaccine, according to research from Israel’s Bar-Ilan University medical school and its affiliated Ziv Medical Center in Safed (Tzfat).

The boost in immunity was seen regardless of when they had been infected and whether or not they had detectable antibodies against Covid-19 prior to receiving the vaccine.

The study adds real-world evidence to the question of the Pfizer vaccine’s effectiveness in recovered Covid patients.

Published February 11 in the journal Eurosurveillance, the study was conducted on a cohort of 514 Ziv staff members including Jews, Arabs and Druze of various ethnicities.

Seventeen of the employees had contracted Covid-19 between one and 10 months before receiving the first dose of the vaccine. Antibody levels of the entire cohort were measured prior to vaccination and thereafter to determine response to the vaccine.

The response among those previously infected was so effective, regardless of ethnicity, that it opens the debate as to whether one dose of the vaccine may suffice.

“This finding can help countries make informed decisions regarding vaccine policy – for instance, whether those previously infected should be vaccinated in priority and, if so, with how many doses,” said study leader Prof. Michael Edelstein, an epidemiologist and public health expert on the Azrieli Faculty of Medicine of Bar-Ilan University.

“It also offers reassurance that not having detectable antibodies after being infected does not necessarily mean that protection following infection is lost,” Edelstein said.

However, the researchers emphasize that their findings should be confirmed in a bigger cohort of a larger age range. The 39 healthcare workers in the study who did not respond strongly to the first dose were older (median age 57 vs. 45) and more likely to be Jewish.

The researchers are continuing to follow healthcare workers after their second dose to better understand how long the vaccine will protect against Covid-19 in different groups of people.