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(WGN) – The BA.2 subvariant omicron is driving COVID-19 cases up in the United States – yes, once again.

The original omicron subvariant (BA.1), which caused a massive spike in COVID-19 cases, hospitalizations and deaths over the winter, was already very contagious. The BA.2 subvariant is even more infectious, said Dr. Justin Fiala, pulmonary and critical care specialist at Northwestern Memorial Hospital.

Early data is showing that even those infected with the BA.1 omicron strain could get sick again with the second subvariant.

“The spike proteins have mutated enough with this new subvariant that even if you were infected back in December or January, you’re not guaranteed to have neutralizing antibodies or the optimally effective antibodies against the newest strain,” Fiala said.

The genetic differences between BA.1 and BA.2 make BA.2 more transmissible, explains the World Health Organization. The difference isn’t huge though – especially when comparing it against two totally different variants. The BA.1 version of omicron was much more contagious than delta, for example. Now, BA.2 is just a bit more contagious than BA.1.

BA.2 now makes up nearly all COVID-19 cases in the United States – about 99% of infections, according to the latest data from the Centers for Disease Control and Prevention.

While it appears to be more contagious, BA.2 doesn’t yet appear to cause more severe illness or death than other types of omicron, according to Yale Medicine. Scientists are still monitoring the newest strain for more signs of differences.

“We always see the cases ticking up before we really know what to make of the severity of illness, or any of the things that come after the initial infection,” said Fiala.

The same things that lower your chance of getting other COVID-19 variants work against BA.2, as well.

“I think the smartest thing anyone can do is start to re-implement a lot of those measures that may have fallen to the wayside as things were down-trending previously,” Fiala said

He added wearing a high-quality mask when around others is still a very effective way to prevent getting sick if COVID-19 is circulating in your community.