Newer, fitter Omicron variants begin to drive their own waves
There's no denying the numbers: Even with spotty reporting, Covid-19 cases and hospitalisations 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.
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.
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 hospitalisations 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.
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. Like BA. 2.12.1, BA. 4 and BA. 5 have a growth advantage over BA.2.
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.
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 neutralise 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 threefold lower.
By way of comparison, the World
Health Organization uses an eightfold drop in neutralisation 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.
Before the SARS-CoV-2 virus, scientists thought coronaviruses didn't change much. Looking back, we didn't know what we didn't know. As long as the virus continues to find hosts to infect, it will continue to evolve.
"This virus has shown that it mutated slowly, but when it started to pick up good mutations, they just kept coming and coming and coming."