Single dose of Pfizer COVID-19 vaccine provokes strong immune response: Study

Jerusalem, Feb 16: People previously infected with the novel coronavirus respond very strongly to single dose of the Pfizer-BioNTech COVID-19 vaccine, regardless of when they were infected and whether or not they had detectable antibodies against the disease prior to receiving the preventive, according to a study.

Researchers from Bar-Ilan University and Ziv Medical Center in Israel noted that the real-world evidence with regard to the COVID-19 vaccine remains scarce even though the clinical trial data are encouraging.

Specifically, the response to the COVID-19 vaccine among those previously infected with the SARS-CoV-2 virus is still not completely understood, they said.

The latest study, published in the journal Eurosurveillance, was conducted on a cohort of 514 staff members at Ziv Medical Center. Seventeen of the participants were infected with COVID-19 anytime between one and ten 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 BNT162b2 mRNA vaccine developed by US company Pfizer and its German partner BioNTech.

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

"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 Professor Michael Edelstein, from Bar-Ilan University, who led the study.

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

The study also provides evidence that immune response was similar across multi-ethnic groups as Ziv Medical Center, where the study was conducted, is staffed by a workforce comprised of Jews, Arabs and Druze, among others.

The researchers noted that the members of each of these groups responded very similarly to the first dose of the vaccine, a welcome finding considering that the virus itself is known to affect some groups more than others.

The strong response to one dose of the vaccine among those previously infected regardless of the duration between infection and vaccination is good news, they said. However, the researchers emphasise that their findings should be confirmed in a larger cohort before reaching definitive conclusions.

The team continues 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.