These 2 New Variants Are Extra-Contagious

Two new extra-contagious variants of omicron with transmissibility similar to measles are together dominating COVID-19 cases in the US, leading to talk of new indoor mask mandates. Here's what you need to know:

• Background: BA.4 was first detected in South Africa in January, while BA.5 was first detected in the country a month later. They are the fourth and fifth omicron subvariants to dominate cases this year following BA.1, BA.2, and BA.2.12.1.
• Makeup: BA.4 and BA.5 appear to have evolved from BA.2. They have identical mutations in the spike protein but different mutations in the body of the virus, as epidemiological methodologist Adrian Esterman writes at the Conversation.

• Dominance: According to CDC estimates, BA.4 and BA.5 together accounted for 52% of new cases in the week ending June 25. BA.4 accounted for 15.7%, while BA.5 accounted for 36.6%, per the New York Times. "BA.2.12.1 is still the most prominent individual variant" at 42%, down from over 63% a month ago, per New York.
• Vaccine effectiveness: These subvariants are especially good at evading immunity from vaccines and previous infections, including those from other omicron variants. Ars Technica looks at the relevant findings from one recent study. On the bright side, early data indicates vaccines continue to protect against hospitalization and severe illness with BA.4 or 5.

• Transmissibility: According to Esterman, research suggests BA.4 and 5 have a basic reproduction number (the average number of people that will be infected by an initial case in a population with no immunity) of 18.6, compared to 9.5 with BA.1 and 13.3 with BA.2. "This is similar to measles, which ... until now was our most infectious viral disease," Esterman writes.
• US surge: More than 100,000 new cases have been reported each day on average in the US for weeks, per the Times, which notes "some scientists estimate that the current wave of cases is the second-largest of the pandemic." Late last month, the US test positivity rate hit a seven-day average of more than 15% for the first time since Feb. 3, reports New York. More than 87% of US counties are experiencing high community transmission, according to the CDC.

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• Talk of masks: Health officials in Los Angeles County, which is experiencing its highest case rate since early February, are warning that new masking rules may be required later this month, as the Los Angeles Times reports.
• New vaccines: Others hope new booster vaccines that specifically target omicron will help stop the spread. Early results suggest Moderna's version will offer better protection against BA.4 and 5. Still, "no one can tell whether retooled vaccines could become outdated by the time they become available," the NY Times reports.

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