PROVIDENCE, R.I. (WPRI) — A newly published study on vaccine efficacy and the risk of COVID-19 reinfections was conducted using Rhode Island health data.

The study, authored by researchers at the Brown University School of Public Health, was recently published in the Journal of the American Medical Association.

Researchers from Brown used R.I. Department of Health surveillance data from March 1, 2020, through December 9, 2021, on COVID-19 vaccinations, laboratory-confirmed cases, hospitalizations and fatalities. The Alpha and Delta strains of COVID-19 were predominant at the time.

Joseph Hogan, a professor and chair of the biostatistics department at Brown, tells 12 News the study involved data from more than 100,000 Rhode Islanders.

The goal of the study was to determine the efficacy of the COVID vaccine when it comes to preventing reinfections, specifically among people who have already recovered from the virus.

Hogan said the study came about when state epidemiologists started wondering whether the vaccines are protective, even after infection, and amid a national conversation about vaccine mandates and whether or not natural immunity held up.

“To our surprise, the benefits of the vaccine were such that on average, they reduced the probability of becoming reinfected by about half,” Hogan said.

Researchers looked at data involving long-term care residents, employees and the general population. Hogan said of that cohort, roughly about 94,000 were in the general population.

“What makes our study stand out is that it’s a prospective cohort of a statewide population. I think that’s probably pretty rare. I don’t know that there are others like it,” he said.

“So the numbers that we were seeing, whether it was long term care or general population, were between 45% and 60% effectiveness, which is which is really quite good for for a vaccine,” Hogan said. “That’s a higher than what we might see for like a flu vaccine, for example.”

Hogan noted the data showed for both employees and residents of long-term care facilities, the infection rate was much higher than the general population for those who remained unvaccinated.

“The benefits of being vaccinated, even after a prior infection and recovery, turned out to be really substantial,” he said.

Hogan said researchers were also surprised to learn that those whose prior infection resulted in a hospitalization were more at risk of contracting the virus again.

“I don’t think we really have a strong explanation for why that is, but that was a pretty strong signal,” he added.

Hogan said no one vaccine proved to be more or less effective than another. His main takeaway from the study is this: if you haven’t gotten the vaccine yet, you should.

“It’s hard to overstate how overwhelmingly supportive the data are for the vaccine and we have looked at it and health systems at the molecular level at every possible level,” he said.

The study was conducted while state-run test sites were open and before at-home tests were relied on.

Hogan noted a change in testing surveillance may make additional studies challenging, but researchers are hoping to do a similar investigation for the Omicron variant.