FAQ: BA.4 and BA.5, potentially the most transmissible Omicron subvariants yet

America’s current COVID-19 surge is being driven by BA.2 and its sublineage BA.2.12.1. But there are other versions of Omicron out there to which we need to pay attention—namely, BA.4 and BA.5. Here’s a brief FAQ on these two subvariants, including why scientists are concerned about them and where they’re spreading in the U.S.

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National numbers, June 5

The BA.2/BA.2.12.1 surge continues. According to the CDC, the number of new cases reported nationwide dropped last week, compared to the prior week; but this drop is more likely a result of the Memorial Day holiday than of an actual slowdown in transmission.

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National numbers, May 29

America’s largely-ignored BA.2 surge continues: the U.S. reported over 100,000 new cases a day last week, while an average of 3,600 new COVID-19 patients were admitted to hospitals each day. Both of these metrics rose about 8% from the week prior.

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National numbers, May 22

The Omicron BA.2 surge continues in the U.S., with a 19% increase in officially-reported COVID-19 cases in the past week to over 100,000 new cases a day. Of course, the official case numbers severely underestimate true infections, as PCR testing sites close and more people use rapid tests; actual case counts may be five or more times higher.

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National numbers, May 15

New COVID-19 cases continue to rise in the U.S., with an average of 85,000 cases reported nationally each day last week—double the daily average from three weeks ago. This is a significant undercount, of course, as the majority of COVID-19 tests conducted these days are done at home.

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Omicron keeps mutating as U.S. cases rise

As though it’s not already confusing enough to distinguish between Omicron BA.1 and BA.2, more sublineages have popped up in recent weeks as Omicron continues to spread and mutate. Here are two that I’m watching, though they don’t seem to be major causes for concern at this time.

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National numbers, April 17

New COVID-19 cases in the U.S. have gone up for the second week in a row, and the increase was sharper this week. While the daily average of new cases (about 31,000) remains low compared to the Omicron surge, this trend is still concerning—especially when factoring in all the at-home rapid tests that are going unreported right now.

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National numbers, April 10

After several weeks in a plateau, new COVID-19 cases in the U.S. are once again going up at the national level. The CDC reported an average of 27,000 new cases a day last week—less than one-tenth of what we saw during the Omicron surge, but still a notable uptick from the week prior.

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