How is the BA.5 COVID-19 variant different from other strains?

The fast-spreading BA.5 subvariant of Omicron and its close relative BA.4 now account for around 95% of COVID-19 cases, according to estimates released Tuesday by the Centers for Disease Control and Prevention (CDC). from the USA.

Stresses have accelerated the pace of new COVID-19 cases this month – President Biden among them. Hospitalizations in some regions are now obscuring the worst days of last year’s delta variant wave, particularly among Americans age 70 and older.

CDC officials say they’re now studying the current wave, with initial results on how the variants affect issues like vaccine effectiveness expected late next month. And data from other countries that have already weathered a wave of falls from BA.5 and its close relative BA.4 could provide clues as to what’s to come.

However, the nature of the pandemic has changed in significant ways, and there is now a broad population of people with previous infections, protection from vaccines, or both. This is a muddy attempt to study the virus.

Fever and sore throat overtake the loss of taste and smell

Data from studies in the UK, as well as the country’s ongoing COVID-19 survey, suggest that the proportion of residents there who have fallen ill is the once characteristic symptoms of loss of taste and smell has dropped significantly since earlier in the pandemic.

This was a shift first observed by scientists around the world during the winter wave of Omicron BA.1 subvariant infections. Instead, the flu-like symptoms of COVID-19 are now being reported more frequently.

“The percentage of people testing positive who reported abdominal pain, fever, sore throat and muscle aches increased in June 2022 compared to May 2022,” the country’s Bureau of National Statistics reported through June 24.

But it’s hard to say how much of this shift is due to a change in the virus itself. Scientists have hypothesized that immunity from previous infections could also play a role in influencing what appear to be the most common symptoms seen during the last Omicron waves.

Reinfections increase

The rate of reinfection has risen sharply in the UK and other countries since the arrival of the Omicron variant over the winter.

Federal researchers have estimated that the BA.4 and BA.5 mutations in 2020 place them among the furthest from the original strain of the virus, and even closer to the beta variant first seen in May 2020 than to its Omicron Cousin BA.1.

Data from Qatar suggest that people who survived pre-Omicron variant COVID-19 infection are only about 15% protected from symptomatic reinfection by BA.4 or BA.5. If the previous infection was from a different Omicron subvariant, this estimate increases to 76%.

Health officials here, for example in Washington state, have also seen a steady increase in reinfections in recent months, although they concede this may be underestimated due to factors such as home testing.

“What’s the closest parallel to what we’re seeing in the US? The UK is the closest, but the UK itself is so far from what we’re seeing here in the US,” said Venky Soundararajan, chief scientist at research firm Reference.

Soundararajan recently collaborated with scientists at the National Institutes of Health to publish research in PNAS Nexus that quantifies the “distinctiveness” of variants compared to those previously circulating in a given region of the world. The authors found that this new metric can predict fluctuations in the future growth of variants in different parts of the world, depending on which variants had previously spread to those regions.

Soundararajan cited the large gap in new COVID-19 cases between the two countries in March, as the UK reported a sharp rise in BA.2 infections at a time when US cases were largely slowing.

Their metric suggests that while BA.5’s significant growth advantage will lead to a spike in some instances, the “immunity wall” built up during the winter wave suggests the current wave won’t reach the same record highs.

“BA.5 Omicron is not significantly different in the US from what we have seen, particularly with BA.2.12.1 being the youngest subtype to be orbited. And BA.1 continues to offer an extremely high level of exposure that we suspect will continue playing throughout the summer,” added Soundararajan.

Rates of serious illness remain lower than previous waves

Even as the pace of COVID-19 hospitalizations across the country has accelerated, readings of some of the disease’s worst outcomes remain far lower than during some previous waves of the pandemic.

Only a relatively small percentage of hospital beds in intensive care units across the country are occupied by COVID-19 patients. The pace of new COVID-19 deaths remains worse than at this point last year, with an “unacceptable” average of more than 300 deaths per day. But even for more vulnerable groups like nursing home residents, the daily death toll from COVID-19 remains a fraction of some previous waves.

Federal health officials have attributed this “decoupling” to protection from vaccinations, particularly additional booster doses, as well as the wider use of COVID-19 treatments like Pfizer’s Paxlovid pills.

A study published last week in the New England Journal of Medicine suggests that currently available COVID-19 drugs will work against subvariants BA.4 and BA.5.

Data from South Africa’s case wave of the two subvariants earlier this year suggests they posed a similar risk of COVID-19 hospitalization and serious illness as Omicron’s original BA.1 subvariant.

However, early research from countries such as Denmark and Portugal suggests that BA.5 may pose a greater risk of hospitalization compared to BA.2. And early lab tests of the subvariant, recently published by scientists in Australia, suggest BA.5 could pose a greater threat thanks to its ability to infect lung tissue.

Home testing may be more effective at detecting BA.5

During the wave of the first Omicron BA.1 subvariant infections back in DecemberFederal health officials acknowledged that early data suggested some rapid home tests appeared to have lower sensitivity in detecting infection compared to previous variants.

“We had seen early in the Omicron era that it seemed like the sensitivity of antigen tests was decreasing. That’s been posted on the FDA website for months. And the data has continued to accumulate that it’s not as sensitive,” said Tim Stenzel of the Food and Drug Administration at a town hall with COVID-19 test manufacturers last month.

At a recent webinar with COVID-19 testing labs, however, Stenzel said the regulator had seen early — if not yet conclusive — data suggesting that BA.5 may have changed, meaning home testing these More likely to detect subvariant.

The regulator has worked with the National Institutes of Health’s RADx program at Emory University and the Georgia Institute of Technology to study the impact of variants on testing.

“There are some reports that there may be fewer low positives. And some early data suggests that might be the case. So we could see improved antigen test performance with BA.5,” Stenzel said last week.

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