New COVID-19 infections may be declining in some states, like Michigan and Vermont, but a challenging summer lies ahead as new omicron variants worry experts.

Driving the news: Subvariants BA.4 and BA.5 are now gaining ground against the dominant strains BA.2.12.1 and BA.2, making up 6% to 7%, respectively, of new infections in the United States last month, according to CNN.

“It’s a serious threat,” Dr. David Ho, a professor of microbiology and immunology at Columbia University in New York City, told CNN.

“Only a month ago, it was .02 percent.”

Why is it concerning: The preliminary research at the Africa Health Research Institute in Durban, South Africa, found that antibodies are much less effective against the new subvariants compared to the original omicron strain.

  • It is because the BA.4 and BA.5 strains carry several mutations that help dodge the barrier of previous vaccinations or infections, according to VaccinesWork, a digital platform covering immunization news.
  • The rate by which the strains are spreading is worrisome, as they dominate new infections in South Africa while being rapidly detected in other places.
  • The two new subvariants had already been detected in several countries by late April, including Austria, the U.K., the U.S., Denmark, Belgium, Israel, Germany, Italy, Canada, France, the Netherlands, Australia, Switzerland and Botswana, according to a U.K. Security Agency report.
  • However, there isn’t enough evidence yet to suggest that these mutations cause a more severe illness.

State of play: The European Centre for Disease Prevention and Control deemed the BA.4 and BA.5 strains as “variants of concern” on May 12.

Between the lines: The Food and Drug Administration is yet to decide on a new COVID-19 vaccine design, in hopes of giving people “the longest duration of a high level of protection” without getting boosted or worrying about another surge every few months, per ABC News.

  • “It’s unclear what the mix will be in the vaccine that’s used in the fall, but there’s a very good chance that it’ll be against the original omicron,” Celine Gounder, an infectious disease specialist and an editor at KHN, told Axios.
  • “But it’s really unclear that it’s going to be much of an improvement versus the original vaccine when BA.4 and BA.5 are so significantly different than the original omicron.”

What is happening in South Africa?: According to Fortune, even though 97% of the population had antibodies from past infection or vaccination, South Africa recently experienced a fifth COVID-19 wave.