If you’ve been wondering if you need another COVID booster shot, the answer is probably yes — at least if you haven’t had one in the past six months or so.

Updated boosters every six months to a year greatly reduced the long-term risk of infection from COVID-19, according to a study by researchers from the Yale School of Public Health and the University of North Carolina at Charlotte. The risk of future infection tripled for those not getting an updated booster shot, compared with annual boosting they found.

“The risk of future infection is strongly linked to the timing of boosting,” one of the lead authors, Jeffrey Townsend, Elihu Professor of Biostatistics at Yale School of Public Health said, in a statement. “Waiting one and a half years nearly doubles the long-term risk of infection compared to boosting annually.”

The risk of future infection tripled for those not getting an updated booster shot.

Boosters don’t just renew one’s protection. Updated vaccines are designed to address new variants arising from changes in the virus that occur as part of its natural evolution over time, the researchers said.

“[W]e are in an arms race against an evolving virus,” the other lead author of the study, Alex Dornburg, an assistant professor at UNC, explained. “As we have now seen with previous vaccines, we need to continue to update boosters to match the circulating strain. We already administer annual vaccines for influenza, and the mRNA technology would make updated vaccinations possible on an even more accelerated timescale.”

The study is the first to quantify the long-term likelihood of future infection following boosting by updated Moderna or Pfizer vaccines. Relying on information from a large number of immunological studies of SARS-CoV-2, the virus that causes COVID-19, and other coronaviruses, it developed a data-driven model of infection risks over time. Because they were using such a large data set, the team was able to analyze the long-term risks of infection as they related to a range of frequencies of boosting.

Getting a booster every six months provided “very strong suppression” of infection, the researchers found. Only one in 10 people who received updated booster shots every six months was projected to contract COVID-19 over a six-year period, according to the study’s analysis.

Three out of 10 people were likely to contract COVID-19 if they received an annual updated booster shot. That figure climbed to nine out of 10 for people who did not get a booster shot at all.

“These results are based on a typical person with a typical immune response following boosting,” Townsend explained. “An important next step will be to quantify the benefits of frequent boosting for those with atypical immune responses due to chemotherapy, immunosuppressants, or other immune challenges.”

The study is published in the Journal of Medical Virology.