(NEXSTAR) – With the rise of the BA.2 variant of COVID-19, a subvariant of omicron that is also called stealth omicron, are people who caught the virus in the last wave susceptible again?

Early research indicates it’s not likely the subvariant will reinfect most people who just caught omicron in this recent wave of cases, but it is possible.

A study of 2 million people in Denmark conducted between November and February found 187 instances of reinfection. Of those 187 cases, 47 were people who had the BA.1 variant, then caught the BA.2 variant.

According to Healthline, the majority of the people in the study who caught both omicron subvariants were young and unvaccinated. They did not have severe cases.

The study has not yet been peer-reviewed.

Eric Feigl-Ding, an epidemiologist and former Harvard researcher, raised a warning flag on Twitter in February, citing other early studies that showed omicron’s protectiveness from reinfection doesn’t last long.

“Our results suggest that Omicron-induced immunity may not be sufficient to prevent infection from another, more pathogenic variant, should it emerge in the future,” he tweeted, quoting the study.

It may seem counterintuitive, but people who only had a mild case of omicron the first time around may also be more likely to get it again.

“If you had a mild infection, didn’t get a very good immune response, and you get exposed again with a big dose of the virus, it’s definitely possible,” Dr. Stanley Weiss, professor at the Rutgers New Jersey Medical School, told Yahoo.

However, because there is so much similarity between the two subvariants of omicron, many people infected in the most recent winter surge could be protected in the short term.

“I think [reinfection] is unlikely because there is so much shared similarity [between the two types] that the minor differences are probably not enough to allow it to evade immunity to omicron,” said Dr. Daniel Kuritzkes, head of Brigham and Women’s Hospital’s infectious disease division, in an interview with WBTS last month.

As with other variants, any added protection you get from a recent omicron infection also wanes over time. About two-thirds of those infected with omicron in the U.K. were people who had caught the alpha or delta variant in past COVID waves, a study from Imperial College London found.

“I suspect over time, yes, you probably can get reinfected. But we don’t have that data yet because omicron has only been around since October/November,” John Hopkins Senior Scholar, Dr. Amesh Adalja, told KHOU.

Protection from the COVID vaccines is more reliable, the Centers for Disease Control and Prevention says. A fully vaccinated person who had a breakthrough infection is best protected against future infection, a recent CDC study found.

Vaccinated and boosted people were also far less likely to have severe symptoms associated with an omicron infection.

The BA.2 subvariant makes up about 23% of COVID-19 cases in the U.S., according to the CDC’s last estimate. Epidemiologists point out its presence has been doubling about every week.