Newer, fitter descendants of Omicron variant begin to drive their own coronavirus waves

 There's no denying the numbers: Even with spotty reporting, Covid-19 cases and hospitalizations are rising again in the United States.

Cases are trending up in most states and have increased by more than 50% compared with the previous week in Washington, Mississippi, Georgia, Maine, Hawaii, South Dakota, Nevada and Montana. In New York, more than a quarter of the state's population is in a county with a "high" Covid-19 community level, where the US Centers for Disease Control and Prevention recommends indoor masking.

Average daily hospitalizations are up about 10% since last week, according to data collected by the US Department of Health and Human Services.

The culprit this time appears to be a spinoff of Omicron's BA.2 subvariant called BA.2.12.1, which was first flagged by New York state health officials in April.

BA.2.12.1, which is growing about 25% faster than its parent virus, BA.2, accounts for nearly 37% all Covid-19 cases across the US, according to new estimates from the CDC.

BA.2 caused an estimated 62% of all Covid-19 cases last week, down from 70% the week before.

US, South Africa contend with faster new variants

BA.2.12.1 isn't the only Omicron offshoot that scientists are watching.

After weeks of declines, South Africa saw its Covid-19 cases rise steeply in the past two weeks. Test positivity and hospitalizations have also popped up as scientists have watched two relatively new subvariants, BA.4 and BA.5, dominate transmission in that country. Taken together, they accounted for almost 60% of all new Covid-19 cases by the end of April, according to South Africa's National Institute of Communicable Diseases.

These new Omicron subvariants are spreading around the globe. BA.4 sequences have been reported in 15 countries and 10 US states, while BA.5 has been picked up in 13 countries and five US states, according to the website Outbreak.info, which maintained by a coalition of academic research centers and is supported by funding from the National Institutes of Health.

Like BA.2.12.1, BA.4 and BA.5 have a growth advantage over BA.2.

Omicron subvariants escape immunity

A new preprint study, published ahead of peer review, is pointing to why BA.4 and BA.5 are gaining ground: They can escape antibodies generated by previous infections caused by the first Omicron virus, BA.1, the variant responsible for the huge wave of infections that hit many countries in December and January. They can also escape antibodies in people who've been vaccinated and had breakthrough BA.1 infections, though this happened to a lesser degree than seen in people who've only been infected.

Researchers in South Africa tested the ability of antibodies in blood to disable BA.4 and BA.5 viruses in a lab. In people who were unvaccinated but recently recovered from a BA.1 infection, they saw a more than seven-fold drop in the ability of their antibodies to neutralize BA.4 and BA.5 viruses. In people who'd been vaccinated but recently had a breakthrough infection caused by BA.1, the drops were smaller, about three-fold lower.

By way of comparison, the World Health Organization uses an eight-fold drop in neutralization as the threshold for the loss of protection that requires an update to seasonal influenza vaccines.

The study results led the researchers to write that "BA.4 and BA.5 have potential to result in a new infection wave," making Covid-19 vaccinations and booster shots crucial to stopping the next wave.

"Our conclusions from this are, first, that Omicron by itself is not a great vaccine, right?" said Alex Sigal, a virologist at the Africa Health Research Institute who led the study. "Just because you were infected does not mean you have a lot of protection from what's coming next."

Dr. Eric Topol, a cardiologist who is the founder and director of the Scripps Research Translational Institute, praised the research, pointing out that this lab was also the first to characterize the first Omicron variant: "They've been first-rate all the way through the pandemic."

He said that overall, the finding was not good news. Even people who recovered from a Covid-19 infection as recently as December or January can be reinfected by these new subvariants.

"That dropoff of immune escape or immune evasion was pronounced in people who were unvaccinated," Topol said, pointing out that only about 1 in 3 people in South Africa have been vaccinated against Covid-19.