Highly contagious BA.5 variant becomes dominant in US as Covid cases rise


The highly transmissible BA.5 omicron subvariant is now the dominant coronavirus strain in the United States, accounting for nearly 54% of Covid-19 infections last week, according to estimates from the Centers for Disease Control and Prevention, as as cases rise and as pharmaceutical companies work to reformulate vaccines to target new virus strains known for their ability to evade antibodies.


BA.5 and the closely related omicron substrain BA.4 accounted for 70% of coronavirus infections for the week ending July 2, according to CDC estimates, which may be subject to change.

The BA.2.12.1 variant, which helped fuel a spike in Covid-19 cases when it was dominant in the spring, accounted for just 27% of cases last week.

The news comes a week after the Food and Drug Administration recommended drug companies update their coronavirus vaccine booster shots by fall to target BA.4 and BA.5, in anticipation of a winter surge of Covid-19.

It also comes as Covid-19 cases have risen in recent months, with the US averaging 94,345 new infections per day in the week ending July 4, more than triple the 30,558 daily cases reported. to April 10, but well below the January peak of more than 800,000 a day.

Hospitalizations are also trending up: Covid-19 hospital admissions averaged 4,376 a day in the seven-day period ending July 3, more than double the average of 1,428 per day in early April, although the numbers are still much lower than in winter. coronavirus outbreak, when daily hospitalizations topped 20,000.

Surprising fact

More than 16% of coronavirus tests in the United States came back positive on average last week, the highest positivity rate since early February, according to the CDC.

Key Context

BA.4 and BA.5 were first discovered earlier this year in South Africa, where the strains became dominant, and they finally made their way to the United States in late March, although the substrain omicron BA.2 remained the dominant variant for several weeks. All three substrains have specific mutations in their spike proteins – the part of the virus that binds to the human cell – that help them evade the immune system, with data suggesting BA.5 is even better at evading the virus. antibodies from previous coronavirus infections and vaccines. Countries around the world like the UK are also seeing a spike in cases as BA.4 and BA.5 become their most prevalent coronavirus strains. BA.4 and BA.5 combined became the dominant substrains of Covid-19 in the United States two weeks ago, accounting for 55% of cases.

To monitor

A continued spike in Covid-19 cases over the summer. The increase in new subvariants that are even more contagious than previous strains and able to evade the immune system suggests “substantial circulation of the virus this summer,” Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, says the the wall street journal Last week.

Further reading

FDA Recommends Covid Boosters Target Highly Contagious Omicron Subvariants – Here’s When You Should Get Your Next Shot (Forbes)

What to Know About the Newest and Most Contagious Omicron Subvariants (Time)

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