Three new signs BA.2 might not hit America as hard as Europe
Is BA.2 about to surge in America the way it’s surging in Europe?
There are already some clues that it might not — and the coming days could provide even more reason for cautious optimism.
Across the pond, the BA.2 subvariant of Omicron — which is at least 30% more transmissible than its sister lineage — has sent COVID-19 case counts soaring again at the very moment when most Western European countries seemed to be putting their massive winter waves behind them.
In the U.K., cases have more than tripled over the last three and a half weeks, skyrocketing from about 27,000 to nearly 87,000 per day. Across the European Union, new daily cases are up more than 70% since the beginning of March. U.K. hospitalizations have been ticking up as well.
For Americans, the fear is that we’re next — that BA.2, which now accounts for 35% of infections nationwide, will inevitably do to us what it is doing to our European counterparts.
But a big U.S. BA.2 surge isn’t as inevitable as it seems. Here are three emerging signs of hope:
1. New York
To figure out how BA.2 will affect the U.S., watch New York, where the subvariant appears to be exactly one month behind the U.K. in terms of prevalence — and ahead of the rest of the States.
COVID’s recent U.K. turnaround followed a clear pattern. BA.2 became the country’s dominant strain around Feb. 20. The British government lifted its last COVID restrictions at exactly the same moment. One week later, daily U.K. case counts bottomed out. Since then, they have increased more than 200%.
The New York region, meanwhile, just became the first in the U.S. where BA.2 is responsible for a majority of COVID cases; according to the Centers for Disease Control and Prevention, the subvariant hit the 52% mark there on or around March 20.
If the U.S. were to follow in the U.K.’s footsteps, cases would start to take off in New York around March 27 — when BA.2 clears 60% or so — and across the country as a whole about a week later.
That might still happen. But there’s at least one major difference between New York and the U.K. to consider. At the moment when BA.2 became dominant in Britain, there was still a ton of virus circulating there; nearly 11% of tests were coming back positive, on average. But now, after an additional month of declining infections, the positivity rate in New York is much lower than that: just 1.9%. So while BA.2 accounts for a similar proportion of cases, it’s actually far less prevalent in New York today than it was in the U.K. one month ago.
And no matter how transmissible a variant is, it’s simply harder for it to spread when there’s less of it around. The latest New York case counts might reflect this dynamic. After flatlining in early March, cases there have started to rise — but they are rising slowly, at a rate of just 17% over the last week. In New York City, they’ve risen just 4% over the last week.
So far, this doesn’t look much like the U.K., where cases started rising at a rate of 67% per week as soon as BA.2 took over. But we’ll see what happens next.
2. Wastewater
The New York region isn’t the only place in the U.S. where BA.2 is dominant, it turns out. By tracking viral RNA levels in local sewage — a speedier way to track new variants than test-based sequencing — molecular virologists have identified other communities where BA.2 now makes up a majority of new cases.
And they’re not seeing explosive case growth there either.
This information might seem to clash with recent headlines and tweets about dramatic increases in SARS-CoV-2 sewage levels — as in, more than 1,000% — at dozens of sampling sites nationwide, which certainly sounds like a leading indicator of a big new wave.
The problem is that this scary-sounding data comes from the CDC’s new National Wastewater Surveillance System, which compiles the latest RNA levels from about 700 sites in three-quarters of the states — but reports only the percentage by which those levels have changed over the last 15 days.
And “that may be deceptive,” as experts at the Pandemic Prevention Institute recently pointed out. “You can have a 1000% increase that takes you from ‘very low risk’ to ‘low risk’. A pretty big % change can still be a small number.”
What’s more, they wrote, “it’s important to see a trend rather than a single data point,” because “without the context of a longer sampling period, it is hard to interpret whether we’re seeing a spike or just more noise.”
A more revealing measure would be to compare case numbers to sewage levels over time in a place where BA.2 is dominant — and that’s precisely what Marc Johnson, a molecular virologist responsible for wastewater data in Missouri, has done.
“Here are the SARS-COV-2 concentrations from the 5 Missouri sewersheds where BA.2 is the dominant lineage,” Johnson tweeted earlier this week alongside a chart showing a bunch of lines that pancaked in March. “With Delta and Omicron the numbers went up immediately after arriving. If BA.2 is going to cause a surge it sure is taking its time.”
Two days later, Johnson took a “closer look” at the “7 sewersheds in Missouri where the wastewater concentrations have increased 1,000% or more,” according to the CDC.
“Some of these might be the beginning of trends, but it is hard to say without more data points,” he wrote. “When infection rates are low (below 1/1,000), the numbers from wastewater can be pretty volatile.”
Furthermore, while “the CDC dashboard is designed to be very sensitive to recent spikes,” he continued, “it is important to compare the number of sites with increases to the number of sites with decreases when deciding if the dynamic of the pandemic is shifting.”
When he did that, Johnson found that “increases and decreases were pretty symmetric” over the past two weeks — suggesting that they’re “probably noise.”
“Overall, numbers went down slightly,” he added.
Looking at similar data on Thursday from Southern Connecticut, where local experts now estimate that BA.2 accounts for more than 80% of new cases, Nathan Grubaugh of the Yale School of Public Health calculated that the subvariant is doubling there every 8.6 days (between half and a third as fast as the original Omicron strain was doubling in December and January).
“Based on the current trends,” Grubaugh tweeted, “the BA.2 case [increase] will be more of a ‘bump’ than a ‘wave’, and certainly nothing like Dec-Jan.”
3. BA.1.1
Why would the U.S. experience a mere bump while Europe suffers another real wave? Behavior — or, more precisely, shifting behavior — probably has a lot to do with it.
It’s possible that what’s happening in Europe is that after a longer period of more serious social distancing, more widespread shutdowns and more prevalent masking, this month’s “full reopening” has triggered a relatively sudden expansion in the number of people everyone is being regularly exposed to. And that, in turn, is making it even easier for the fastest variant to find anyone who didn’t have Omicron (not to mention anyone with waning vaccine protection against infection). Mobility data shows that Brits are no longer moving around less as cases rise — they’re just barreling through.
The U.S. is different. While a few liberal states and cities only recently lifted their mask mandates, much of the country returned to “normal” long ago. It’s unlikely, in other words, that changing behavior will make as much difference in the United States as it’s making in Europe, for the simple reason that U.S. behavior isn’t really changing all that much. Perhaps some older and more cautious Americans are starting to encounter wider circles; perhaps that will affect the U.S. curve in the coming weeks. But for the most part, America has already been letting the virus rip.
It also matters which version of the virus we’ve been letting rip. The strain that caused America’s enormous winter wave was actually BA.1.1 — a more aggressive version of Omicron than plain old BA.1, which is the strain that initially hit Europe.
“The majority of the pandemic in the United States recently has been BA.1.1, which is a fraction of the BA.1 family that appears to be more transmissible than the original — not as transmissible as BA.2, but a little more transmissible,” Harvard epidemiologist Bill Hanage said in a recent podcast. “Basically, BA.2 has come over here, and instead of competing with BA.1, it’s actually finding it’s got something a bit more seriously competitive to try and be beating out. So that could explain why it hasn’t been taken over so quickly here.”
Having a worse version of Omicron wasn’t so great over the winter; an estimated 45% of Americans were infected by the variant. But it may be helping the U.S. now by (1) maximizing the amount of population-wide protection against reinfection with BA.2 (which is possible but rare for those who contracted BA.1), and (2) preventing BA.2 from kicking into exponential growth mode. And warming weather could help tamp down transmission as well.
“There’s going to be a bump, and it’ll be bigger in some places and others,” Hanage said. But “I don’t think it’s going to be as dramatic as Europe, because the recent pandemic history has been really quite different.”
None of which is to say the U.S. should let down its guard.
If BA.2 does take off in the States, Americans remain more vulnerable to hospitalization and death than their European counterparts. Just 64% of the U.S. population has received two shots; just 29% has received three shots. The U.S. ranks 65th and 70th, respectively, on these two crucial metrics. Among those who need protection the most — seniors — the U.S. has a booster rate of just 65%. In the U.K. and many European countries, that number is 90% or more. Studies show that without a booster, even “fully vaccinated” seniors are 10% to 20% less protected against Omicron hospitalization and death. Millions of U.S. seniors remain entirely unvaccinated as well.
At the same time, an estimated 7 million Americans are immunocompromised; no children under 5 have been vaccinated; and “long COVID” looms as a real concern. Meanwhile, America’s last modest safety measures — namely, indoor mask requirements in public places and schools — have just been lifted.
As a result, experts say now is the time to prepare for the worst, even as we hope for the best. Mask mandates are unlikely to return so soon after they were lifted, but studies do show, as the CDC’s Greta Massetti put it last month, that people who choose to “wear high-quality masks [such as N95s, KN95s and KF94s] are well protected even if others around you are not masking.” Meanwhile, the Biden administration has asked for at least $15.6 billion to keep variants like BA.2 from upending society by expanding surveillance, updating vaccines, securing therapeutics, improving ventilation and stockpiling masks and tests. So far, both Democrats and Republicans in Congress have refused to provide that funding.
“We need this money,” a senior administration official told reporters last week, pointing to looming shortfalls in the ability to manufacture and widely distribute tests, therapeutics and vaccines. “Time is not on our side. We need this funding immediately.”
If the U.S. does dodge the BA.2 bullet, it wouldn’t be unprecedented. The Alpha variant — which was 50% more transmissible than the original version of the virus — decimated the U.K. last winter, prompting fears of a spring surge in the United States. Yet while the proportion of U.S. Alpha cases kept going up, the total number of COVID cases kept going down. Ultimately, Michigan was the only state where Alpha really caught fire. The rest of the country was largely spared.
But experts also warn that whatever versions of the virus come after Omicron and BA.2 won’t necessarily be “milder” — and that concerning new variants are likely to materialize someday.
That’s why “you use the quiet periods to do the hard work,” as Jennifer Nuzzo, an epidemiologist at Johns Hopkins Bloomberg School of Public Health, recently told the New York Times. “You don’t use the quiet to forget.”
0 Response to "Three new signs BA.2 might not hit America as hard as Europe"
Post a Comment