High protection after one vaccine dose for COVID-19 survivors: study

A health worker gives a shot of the Moderna vaccine at a Puerto Rico National Guard vaccination center during a priority Covid-19 vaccination program for the residents of the island of Vieques, Puerto Rico. (AFP)

Washington, United States — A person who has previously had COVID-19 and receives a single dose of either the Pfizer or Moderna vaccines is equally or better protected than someone who never had COVID-19 and got two doses, according to a study.

The paper was published in the New England Journal of Medicine on Wednesday and led by scientists at the Icahn School of Medicine at Mount Sinai in New York.

The team looked at blood samples from 110 people, 67 of whom had not previously been infected and 43 who had.

All participants received either the Pfizer or Moderna vaccines, which are based on new RNA (ribonucleic acid) technology.

They found that participants who had been infected with the coronavirus before they received their first shot "rapidly developed uniform, high antibody titers within days after vaccination."

"Titer" refers to blood concentration.

The scientists repeatedly sampled the participants and found that in the days following the first shot, antibody levels in those with previous infection were 10 to 45 times higher than those who weren't previously infected.

By the time both groups received their second shots, antibody levels among those previously infected still registered six times higher than those who weren't previously infected.

But "no increase in antibody titers was observed in the COVID-19 survivors who received the second vaccine dose," the scientists wrote, indicating the booster was of limited benefit for people previously infected.

No substantial difference in antibody production was noticed between the two vaccines.

The team also looked at whether side effects differed in people with previous infection versus those without, studying 230 participants.

Overall, there were no serious side effects that led to hospitalization.

Vaccine recipients with preexisting immunity were found to have a higher frequency of mild to moderate side effects like fatigue, headache, chills, muscle pain, fever, and joint pain.

But the team cautioned that limited data was available and more research was needed to confirm the trend.