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 make up around 95% of COVID-19 cases in the U.S., according to estimates published Tuesday by the Centers for Disease Control and Prevention (CDC).
The strains have driven an acceleration this month in the pace of new COVID-19 cases — President Biden among them. Hospital admissions in some regions now eclipse the worst days of the Delta variant wave last year, especially among Americans aged 70 and older.
CDC officials say they are now studying the current wave, with early results on how the variants are impacting issues like vaccine efficacy due by later next month. And data from other countries that have already survived a wave of cases from BA.5 and its close relative BA.4 could offer clues on what is to come.
However, the nature of the pandemic has changed in important ways, and there is now a wide swath of people with prior infections, protection from vaccines, or both. This is muddying attempts to study the virus.
Fever and sore throat overtake loss of taste and smell
Data from studies in the United Kingdom, as well as the country's ongoing COVID-19 survey, suggest that the share of sickened residents there reporting the once-hallmark symptoms of loss of taste and smell has fallen significantly since earlier in the pandemic.
This was a shift first observed by scientists around the world during the wave of Omicron BA.1 subvariant infections over the winter. Instead, COVID-19's flu-like symptoms are now more commonly reported.
"The percentage of people testing positive who reported abdominal pain, fever, sore throat, and muscle ache have increased in June 2022 compared with May 2022," the country's Office for National Statistics reported through June 24.
But it's hard to say how much of that shift is due to a change in the virus itself. Scientists have hypothesized that immunity from prior infections could also be playing a role in affecting what appear to be the common symptoms seen during the latest Omicron waves.
Reinfections surging
The rate of reinfections has surged in the U.K. and other countries since the arrival of the Omicron variant over the winter.
Federal researchers have estimated that BA.4 and BA.5's mutations place them among the most distant from the original strain of the virus in 2020, and closer even to the Beta variant first seen in May 2020 than to its Omicron cousin BA.1.
Data from Qatar suggests people who survived a COVID-19 infection before the Omicron variant have only around 15% protection against a symptomatic reinfection by BA.4 or BA.5. If the previous infection was from another Omicron subvariant, that estimate rises to 76%.
Health authorities here, for instance, in Washington state, have also noted a steady increase in reinfections over the past few months, though they acknowledge that this may be underestimated because of factors like home testing.
"What is the closest parallel to what we are seeing in the U.S.? The U.K. is the closest, but the U.K. itself is so far removed from what we are seeing in the U.S. here," said Venky Soundararajan, chief scientific officer at research company Nference.
Soundararajan recently worked with National Institutes of Health scientists to publish research in PNAS Nexus quantifying the "distinctiveness" of variants, relative to those that have spread previously within a specific region of the world. The authors found that this new metric could predict variations in future increases in variants in different parts of the world, depending on which variants had previously spread in those regions.
Soundararajan cited the wide gap in new COVID-19 cases during March between the two countries, when the U.K. reported a sharp increase in BA.2 infections at a time when cases in the U.S. were largely slowing.
Their metric suggests that while BA.5's significant growth advantage will fuel a surge in cases, the "immunity wall" built up during the winter wave suggests the current wave will not reach the same record heights.
"BA.5 Omicron is not significantly distinct in the U.S., from what we have seen, particularly with BA.2.12.1 which was the most recent subtype that circulated. And BA.1 continues to provide a level of extremely high exposure which we suspect will continue to play out through the summer," added Soundararajan.
Rates of severe disease remain lower than in previous waves
Even as the pace of COVID-19 hospitalizations has accelerated around the country, measurements of some of the worst outcomes of the disease remain far lower than during some previous waves in the pandemic.
Only a relatively small percentage of hospital intensive care unit beds around the country are taken up by COVID-19 patients. The pace of new COVID-19 deaths remains worse than at this time last year, at an "unacceptable" average of more than 300 deaths per day. But, even among more vulnerable groups like nursing home residents, COVID-19's daily death toll remains a fraction of some previous waves.
Federal health authorities have chalked this "decoupling" up to protection offered by vaccination, especially additional booster doses, as well as broader use of COVID-19 treatments like Pfizer's Paxlovid pills.
A study published last week in the New England Journal of Medicine suggests the currently available COVID-19 drugs will work against the BA.4 and BA.5 subvariants.
Data from South Africa's wave of cases from the two subvariants earlier this year suggest they posed a similar risk of COVID-19 hospitalization and severe disease compared to the original BA.1 subvariant of Omicron.
However, early research from countries like Denmark and Portugal now suggest that BA.5 may pose a greater risk of hospitalization compared to BA.2. And early lab tests with the subvariant, like those recently released by scientists in Australia, suggest BA.5 might pose a greater danger thanks to its ability to infect lung tissue.
Home tests may be more effective in detecting BA.5
During the wave of the first Omicron BA.1 subvariant infections back in December, federal health officials acknowledged that early data suggested that some at-home rapid tests appeared to have lower sensitivity at detecting infections compared to previous variants.
"We had seen, early in the Omicron era, that it looked like antigen tests were seeing a decrease in sensitivity. That's been posted on the FDA website for months now. And the data has continued to accumulate that it is not as sensitive," the Food and Drug Administration's Tim Stenzel said at a town hall last month with COVID-19 test manufacturers.
However, at a recent webinar with COVID-19 testing laboratories, Stenzel said the regulator had seen early — if still inconclusive —data suggesting that may have changed with BA.5, that is, that the home tests are more likely to detect this subvariant.
The regulator has been working 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 tests.
"There are some reports that there may be fewer low positives. And some of the early data suggests that that may be the case. So we could see improved antigen test performance with BA.5," Stenzel said last week.