Where the U.S. stands in its battle against COVID-19

The World Health Organization declared COVID-19 a global pandemic two years ago, and now, epidemiologists and public health experts are ready to talk about the virus becoming endemic. Across the United States, cities and schools continue to relax their COVID-19 mask mandates, while scientists are keeping an eye on the BA.2 subvariant that is accounting for more and more infections. When it comes to COVID, there's a lot going on — here's what you need to know:

What is the BA.2 subvariant?

BA.2 is a subvariant of Omicron, and is highly transmissible — it's estimated to be between 30 and 60 percent more contagious than Omicron. As of Tuesday, BA.2 accounted for almost 35 percent of COVID-19 cases in the United States, the Centers for Disease Control and Prevention said, up from 23 percent a week earlier. It's most prevalent in Massachusetts, New Hampshire, Connecticut, and Maine, having been detected in more than 50 percent of cases in those states.

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Should Americans start worrying about BA.2?

Even though it's more transmissible, many experts say they don't envision BA.2 leading to a spike in hospitalizations and deaths in the United States. On Thursday, the daily average number of new cases in the U.S. was 30,387, down 15 percent from two weeks earlier. Dr. John Brooks, a medical epidemiologist and chief medical officer for the CDC's COVID-19 response, told NBC News new data suggests BA.2 is "going to keep growing." However, because Omicron swept across the country during the winter, those who were infected during the surge likely have higher immunity from BA.2 and other subvariants. "Prior infection with the original Omicron appears to confer protection," Brooks said. "Not necessarily against infection but definitely against severe disease and death." Vaccination also continues to offer defense against the virus.

What should people do to prepare for a potential surge?

Get vaccinated and boosted, if eligible. "We have fair warning," Brooks told NBC News. "We are swimming in vaccine in this country. You can get it for free. Go do it." People should also continue to wear masks while inside public spaces, even if mandates have been dropped, and get tested before and after attending events, he recommended.

Are we getting closer to a COVID-19 vaccine for kids 5 and under?

On Wednesday, Moderna announced that data from a recent trial shows its COVID-19 vaccine generated a strong immune response in kids between 6 months and 6 years old. About 6,900 children participated in the trial, and received a quarter of the dose given to adults. Most of the side effects reported were "mild or moderate," Moderna said, with zero cases of the rare heart condition myocarditis. Moderna said it will submit the data to the Food and Drug Administration within the next few weeks, and intends to seek emergency use authorization for the vaccine in kids 6 and under. The company also said it is getting ready to evaluate booster doses for all children.

When might COVID-19 enter its endemic stage?

When a disease is "endemic," it's still present in the population and causing individual cases, but can be managed better and is more predictable than in the pandemic stage. One example is influenza — most strains are endemic because public health experts can reasonably predict when flu season will start and end, and know precautions people can take (vaccination, wearing masks) in order to go about their lives as normal as possible.

Everyone wants to reach the endemic stage, Charlotte Baker, an epidemiology professor at Virginia Tech, told NPR, but "the problem hanging over all of us is what happens if a new variant should occur." If a new variant emerges that is worse than previous ones, the endemic stage will be pushed back.

The goal is to be at "a very low endemic disease pattern," Dr. John Swartzberg, an epidemiologist at UC Berkeley, explained to ABC 10. "That's critical. A really high pattern is not going to be good for anybody." Vaccination will still be key, and even in the endemic stage, those who are unvaccinated or have underlying risk factors could still wind up in the hospital. It's also important to note that malaria, which caused an estimated 627,000 deaths in 2020, is also considered endemic in some countries.

Could COVID-19 ever be eradicated?

That's unlikely. COVID-19 has been found in animals, like deer and hamsters, and "once you have a disease with an animal reservoir, it's very hard to eradicate," Dr. Isaac Weisfuse, an epidemiologist and adjunct professor at Cornell University, told NPR. Case in point: in Hong Kong, it's believed that at least three COVID-19 cases can be linked to hamsters at a pet store. While international health authorities say the risk of transmission is low, it is always possible that once a disease is in an animal, it can make its way to humans, Weisfuse said.