While experts agree that vaccination remains the "safest route" to achieving immunity from COVID-19, a new study published in The Lancet reveals that prior infection provides protection "at least equivalent if not greater than that provided by two-dose mRNA vaccines." Here are the potential implications for vaccine policy going forward.

Study details and key findings

In a systematic review and meta-analysis, the researchers examined data from 65 studies across 19 countries that were published up until Sept. 31, 2022. The studies include retrospective and prospective cohort studies and test-negative case-control studies.

The studies included participants who had prior infections but were not vaccinated, those who were not vaccinated and not infected, and control groups of people who were vaccinated against COVID-19. Any studies that included participants with hybrid immunity, or people who had been both vaccinated and infected, were excluded.

Overall, the researchers found that natural immunity from a COVID-19 infection remained highly protective against hospitalization and death for several different variants at 40 weeks. In particular, prior infection was 90.2% protective for the ancestral, alpha, and delta variants, and 88.0% protective against omicron BA.1.

Although protection against reinfection declined over time, it remained relatively high for pre-omicron variants at 78.6% at 40 weeks. In comparison, protection against reinfection by omicron BA.1 was 36.1% at 40 weeks.

Overall, the "analysis suggests that the level of protection from past infection by variant and over time is at least equivalent if not greater than that provided by two-dose mRNA vaccines," the researchers wrote.

However, they noted that vaccination remains the recommended route to immunity against COVID-19 since there are still considerable risks from infection, particularly among those who are unvaccinated.

"The problem of saying 'I'm gonna get infected to get immunity' is you might be one of those people that end up in the hospital or die," said Christopher Murray, the director of the Institute for Health Metrics and Evaluation (IHME) at the University of Washington and the study's senior author. "Why would you take the risk when you can get immunity through vaccination quite safely?"

The study authors agreed that vaccination remains the safest route to immunity.

Commentary

"This is really good news, in the sense that protection against severe disease and death after infection is really quite sustained at 10 months," Murray said.

According to the researchers, the findings could have implications for policymaking going forward, particularly for vaccination requirements or the timing of booster doses.

The study "supports the idea that those with a documented infection should be treated similarly to those who have been fully vaccinated with high-quality vaccines," the researchers wrote.

Going forward, Caroline Stein, one of the study authors from IHME, said that "decision makers should take both natural immunity and vaccination status into consideration to obtain a full picture of an individual's immunity profile."

Because natural immunity offers similar protection to vaccination, people who have been recently infected may be better off waiting a few months before they get a booster. Currently, CDC recommends people wait three months after an infection to get booster.

However, Deepta Bhattacharya, a professor of immunobiology at the University of Arizona, said that those with healthy immune systems may be able to wait six months before they get a booster dose to allow the immune response to develop more fully.

"We know that the immune response continues to mature over the course of about six months, both for vaccines and for infections," he said. "Waiting about six months gives you the best bang for your buck."

In addition, Bob Wachter, chair of the department of medicine at the University of California, San Francisco, said that while it's not harmful if someone gets boosted sooner than six months, people who have recently had COVID-19 have more flexibility with their timing.

"If you are thinking about getting a booster, it's a perfectly reasonable call to look at this and say I'll wait six or eight months before getting my booster," Wachter said. "That's a reasonable conclusion from looking at the study." (Syal, NBC News, 2/16; Hein, MedPage Today, 2/17)