(NEXSTAR) – So just how long will natural immunity last after catching COVID-19? It might not be as long as you think.

A study from researchers at Yale University and the University of North Carolina at Charlotte found that, on average, unvaccinated people should expect to be reinfected with COVID-19 every 16 to 17 months.

Since COVID-19 hasn’t existed for enough time to perform a long-term study, researchers led by Jeffrey Townsend, Yale professor of biostatistics, examined reinfection in a close viral relative to replicate the immune system’s response, according to the Yale Daily News.

“The overall goal of the study was to provide an answer to a question that at this point in the pandemic would be impossible to answer empirically, which is how long after you’ve been infected by SARS-CoV-2 can you expect to possess immunity against the virus before you become vulnerable to reinfection?” co-author Hayley Hassler, a research associated at the Yale School of Public Health, told the paper.

The findings contradict the notion that recovering from COVID-19 will guarantee a lifetime of protection from the virus.

The study looked at post-infection data from six coronaviruses that are close relatives to COVID-19, dating as far back as 1984. The time period following infection ranged from 128 days to 28 years under endemic conditions, meaning that the disease is constantly found in a population.

Using that data, researchers were able to estimate the reinfection time for unvaccinated people — roughly 16 months on average. That’s less than half the time it takes to get reinfected by other coronaviruses transmitted by humans, they found.

“Reinfection can reasonably happen in three months or less,” Townsend explained in a university news release. “Therefore, those who have been naturally infected should get vaccinated. Previous infection alone can offer very little long-term protection against subsequent infections.”

The reinfection window in the study is an average, the study emphasized, so some people may get reinfected in months while it could take years for others.

“Our results are based on average times of waning immunity across multiple infected individuals,” Hassler told the Yale Daily News. “Any one of those individuals may experience longer or shorter durations of immunity depending on immune status, cross-immunity, age and multiple other factors.”

The findings shed light on valuable data for public health decision-makers, according to the study’s authors, as reinfection is “likely to become increasingly common.”

The researchers say preventative health measures and the global acceleration of the vaccine effort will be “critical” to minimizing COVID-19 deaths.

According to the Centers for Disease Control and Prevention, 57.2% of the U.S. population is fully vaccinated and 66.2% of residents have received at least one shot.