• Omicron BA.5 is becoming the dominant COVID strain in the US. 
• One expert called it “the worst version of the virus that we’ve seen.”
• It is 4 times more resistant to antibodies and may reinfect people in a matter of weeks.

Health experts in the US and abroad have found that the coronavirus variant currently responsible for most infections in the US, Omicron BA.5, can quickly reinfect people who already have protection against the virus. 

People who have been vaccinated, received antibody treatments, or developed natural immunity from contracting the virus were previously thought to have a lower risk of getting COVID-19, at least in the months following exposure.

However, Chief Health Officer of Western Australia Andrew Robertson told news.com.au that he’s seeing people get reinfected with COVID-19 in a matter of weeks.

“What we are seeing is an increasing number of people who have been infected with BA2 and then becoming infected (again) after four weeks,” he said. “So maybe six to eight weeks (later) they are developing a second infection, and that’s almost certainly either BA4 or BA5.”

As of July 2, Omicron BA.5 was responsible for about 53% of COVID infections in the US, according to the Centers for Disease Control and Prevention. BA.4, another contagious Omicron subvariant, accounted for 16.5% of the infections.

Reinfections with BA.5 and BA.4 are typically less severe compared to early COVID infections, David Dowdy, MD, epidemiologist at the Johns Hopkins Bloomberg School of Public Health, told Insider. As the virus has evolved some resistance to antibodies, immune systems are also learning to respond to it without making the body go haywire, he said.

Latest subvariants are extra resistant to antibodies

Like previous Omicron subvariants, BA.5 and BA.4 s are known to have mutations that let them evade protection against the virusfrom COVID-19 vaccines or prior infections.

While the immune system still churns out antibodies to neutralize a potential infection, that protection tapers off over time. It’s not an on-off switch, Dowdy said — but if someone is exposed to a tricky subvariant as their protection is waning, the virus may find an opening.

“Anything that can get around that immune response just a little bit faster has an advantage when a lot of the population is immune,” Dowdy told Insider.

A recent study out of Columbia University that has not yet been peer-reviewed found that the recent BA.4 and BA.5 subvariants are at least four times more resistant to protection against the virus compared with previous variants in the Omicron lineage.

Researchers led by David Ho, MD, director of the Aaron Diamond AIDS Research Center, took antibodies from people who had received at least three doses of an mRNA vaccine, or got two shots and were then infected with Omicron. In a lab study, they watched to see how these antibodies performed against Omicron subvariants.

Compared with their predecessors, the BA.4 and BA.5 subvariants were at least four times more resistant to antibodies, increasing the risk of reinfection in vaccinated people.

Peter Chin-Hong, a University of California, San Francisco infectious disease expert, told the Los Angeles Times that variants BA.4 and BA.5’s “superpower is reinfection.”

Meanwhile, Dr. Eric Topol, director of the Scripps Research Translational Institute in La Jolla, called BA.5 “the worst version of the virus that we’ve seen” in a recent blog post due to its ability to evade immunity and increased transmissibility.