DELTA ON THE RUN: IS THIS THE US’S LAST COVID SURGE?
Rising immunity, behavioural changes may explain recent decline in cases.
After a brutal summer surge, driven by the highly contagious delta variant, the coronavirus is again in retreat. The United States is recording roughly 90,000 new infections a day, down more than 40% since August. Hospitalisations and deaths are falling, too. The crisis is not over everywhere — the situation in Alaska is particularly dire — but nationally, the trend is clear, and hopes are rising that the worst is finally behind us ... again.
Over the past two years, the pandemic has crashed over the country in waves, inundating hospitals and then receding, only to return after Americans let their guard down. It is difficult to tease apart the reasons that the virus ebbs and flows in this way and harder still to predict the future.
But as winter looms, there are real reasons for optimism. Nearly 70% of adults are fully vaccinated, and many children younger than 12 are likely to be eligible for their shots in a matter of weeks. Federal regulators could soon authorise the first antiviral pill for Covid-19.
“We are without a doubt in a better place this year than we were last year,” said Dr Nahid Bhadelia, director of the Center for Emerging Infectious Diseases Policy and Research at Boston University.
But the pandemic is not over yet, scientists cautioned. Nearly 2,000 Americans are still dying every day, and another winter surge is plausible.
Given how many Americans remain unvaccinated and how much remains unknown, it is too soon to abandon basic precautions, they said.
“We’ve done this again and again, where we let the foot off the pedal too early,” Dr Bhadelia said. “It behooves us to be a bit more cautious as we’re trying to get to that finish line.”
When the first wave of cases hit the United States in early 2020, there was no Covid vaccine, and essentially no one was immune to the virus. The only way to flatten the proverbial curve was to change individual behaviour.
That is what the first round of stay-at-home orders, business closures, mask mandates and
bans on large gatherings aimed to do.
There is still debate over which of these measures were most effective, but studies suggest that, collectively, they made a difference, keeping people at home and curbing the growth of case numbers.
These policies, combined with voluntary social distancing, most likely helped bring the early surges to an end, researchers said.
“And then the measures would be lifted, maybe memories would fade,” said Jennifer Nuzzo, a public health researcher at Johns Hopkins University.
Eventually, cases would rise again, and similar patterns would play out. Businesses and local governments would reimplement restrictions, while people who had begun venturing out into the world again would hunker down and mask up.
“The curve is shaped by public awareness,”
Dr Nuzzo said. “We’re sort of lurching between crisis and complacency.”
Delta arrived during a period of deep pandemic fatigue and at a moment when many vaccinated Americans felt as if they could finally relax. Data suggests that the new variant prompted less profound behavioural change than previous waves.
In mid-July, just 23% of Americans said that they always wore a mask in public, the lowest percentage since March 2020, according to the Institute for Health Metrics and Evaluation at the University of Washington.
By Aug 31, the peak of the delta wave, that figure had risen to 41%, although it remained far below the 77% of people who reported wearing masks during the winter surge.
“If you just look around, people are much more living a normal life or a pre-Covid life,” said Dr Christopher Murray, director of the institute.
Still, even modest changes in behaviour can help slow transmission, especially in combination, and delta prompted changes at both the individual and organisational levels.
Schools adopted new precautions, companies postponed reopenings, and organisations cancelled events, giving the virus fewer opportunities to spread.
Meanwhile, more temperate autumn weather arrived, making it possible for Americans in many regions of the country to socialise outside, where the virus is less likely to spread.
Behavioural change is a temporary, shortterm way to drive cases down. The true end to the pandemic will come through immunity.
The delta wave was the first major, national surge to occur after vaccines had become widely available, providing many adults with substantial protection against the virus. (Delta also probably led more Americans to get vaccinated.)
At the same time, the variant was so infectious that it spread rapidly through vulnerable populations, conferring natural immunity on many unvaccinated Americans.
Although neither vaccination nor prior infection provides perfect protection against the virus, they dramatically reduce the odds of catching it. So by September, the virus had a substantially harder time finding hospitable hosts.
“Delta is running out of people to infect,” said Jeffrey Shaman, an infectious disease public health researcher at Columbia University.
What comes next is hard to predict, but cases may not necessarily continue their steady decline, scientists warned. Britain and Israel, which both have higher vaccination rates than the United States, are still struggling with outbreaks.
Most experts said they would not be surprised to see at least a small increase in cases later this fall or this winter as people begin spending more time indoors and travelling for the holidays.
But because the vaccines remain highly effective at preventing hospitalisation and death, any coming winter spikes may be less catastrophic than last year’s.