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The United States has entered the fourth wave of the pandemic – or the fifth, depending on which expert you ask. As the vaccination campaign lags and the contagious delta variant spreads, cases and hospitalizations are at their highest level since last winter. Deaths from COVID-19 are also on the rise.
However, after every other peak there was a trough, often for reasons that were not immediately obvious. In Britain, where the variant is also the dominant form of the coronavirus, daily cases have gone from a peak of 60,000 in mid-July to half in two weeks, although they have since increased again.
In India, the number has reached over 400,000 daily cases this spring; experts estimated that the actual figure could be more than 20 times higher. The unimaginable toll shocked many who said the country had managed to escape the virus. But then, in June, the infections dropped dramatically.
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Scientists are struggling to understand why the delta epidemics in these countries have dissipated, even temporarily, and what that may mean for similar outbreaks, including the one in the United States.
In the United States, the pace of the variant has slowed and new infections are declining in some states, such as Missouri, this delta has hit hard. The number of infections over the past week is now 14% higher than two weeks ago, a fraction of the rate through much of July and early August.
Is the delta push starting to slow down in the United States? Or does the variant put the country on track for months of bumps and valleys?
Expert opinion varies widely on the direction of the virus in the coming months. A number of national forecasts tracked by the Centers for Disease Control and Prevention predict that cases will increase in the first weeks of September – but many predict the opposite.
“Whatever slowdown we have, I think, will be quite slight,” said Dr. Celine Gounder, epidemiologist and infectious disease specialist at Bellevue Hospital Center in New York. “We are at this tipping point where the start of the school year will bring us back to growth at some point. “
Gounder predicted that cases in the United States would rise again in September before declining in October. The virus may have burned unvaccinated segments of the population this summer, Gounder said, but others remained vulnerable.
“I don’t think that means everyone who was susceptible got infected,” she said. “I think people tend to have a false sense of security about it. “
As school children and some office workers start to mingle in greater numbers this fall, for example, resurgences can appear, she said.
Other epidemiologists said they were encouraged by trends in southern states where schools had already opened, noting that while infections were increasing in children, they were also decreasing in adults.
It is important “not to extrapolate too much” from the delta course through Britain and India, Gounder added. The three countries vary widely in the percentage of the population vaccinated, the age of the vaccinated, the adoption of large gatherings and open schools, and the prevalence of masks and other precautions.
Even time can play a role. Infections in Britain have declined in the summer, while the United States heads into the fall with a huge case burden. More people congregating inside will mean more possibilities for the virus to spread.
Delta’s journey through the United States is heavily dependent on vaccination rates, social behaviors, weather and varying levels of precautions, epidemiologists said. Week after week, cases are now declining in a number of southeastern states and California, but increasing in much of the Midwest and northeast.
The variant is believed to be more contagious than previous versions of the coronavirus, as those infected carry it in significantly greater amounts in their airways.
This makes the variant particularly adept at exploiting transmission opportunities – the crowded nightclub, the classroom with an unmasked teacher. But it also means that even modest restrictions, like masking and distancing, can drive the numbers down.
In the Netherlands, where 62% of the population is fully vaccinated, cases rose 500% after the country lifted restrictions. This forced the government to reintroduce some measures, including closing nightclubs and limiting dining hours indoors, leading to a rapid drop in the number of new cases.
In mid-June, three weeks after the start of Britain’s delta surge, cases stopped climbing as quickly as they had been, said Paul Hunter, professor of medicine at the University of East Anglia and World Health Organization adviser on COVID-19.
One major event changed everything: the European Football Championships, a month-long series of matches featuring an exceptionally strong England side that filled pubs and lounges from mid-June. Cases have skyrocketed among young people and the unvaccinated, especially among men.
“Because the Delta is so much more contagious, it tends to pass through communities a lot faster,” Hunter said. “And if it’s more contagious, it’s going to engulf the remaining susceptible people more quickly.”
Britain is now approaching a point of what Hunter described as an endemic equilibrium, where cases are leveling off as more people develop immunity to past vaccination or infection, albeit more others see their level of protection gradually fade.
Bill Hanage, epidemiologist at Harvard TH Chan School of Public Health, said: “After schools close, after football is over and after regular contact networks have reasserted themselves, delta has fewer places to go and he collapses. “
But Hunter warned that the extent to which infections stabilize remains highly dependent on how and where people mix, as well as the season.
After Britain’s daily new cases halved from mid-July to the end of July, they started to climb again. In recent weeks, Hunter said, the increase has been due to outbreaks in areas that had seen relatively few cases earlier in the pandemic and, as a result, had less naturally acquired immunity, including the south. -West of England and rural Scotland and Northern Ireland.
The variant took a different course in largely unvaccinated India. In the months leading up to the second wave, as cases declined and hospitals emptied, life had returned to normal in many parts of India.
In early March, the government declared the country to be in “the final stages of the pandemic,” and Prime Minister Narendra Modi sanctioned overcrowded election rallies in several states, as well as the Kumbh Mela festival, which drew millions of people. faithful. Weddings, cricket matches and family reunions were in full swing.
In the weeks that followed, millions of people fell ill and thousands died. Hospitals in several major cities have been overwhelmed by the depletion of oxygen and other essential supplies. But cases have dropped almost as quickly as they started, especially in the worst-affected states.
Although India’s official case tally is likely an underestimate, the drop cannot be attributed to a decrease in testing, said Bhramar Mukherjee, a biostatistician at the University of Michigan.
“We always predicted the second wave would be big and lean,” Mukherjee said. “If you increase this quickly, the decline is also steep because you are quickly burning the sensitive population.”
Antibody tests suggest the proportion of infected Indians rose to 67% in July from 21.5% in January. Antibody tests may not be reliable, but if those numbers come close to accuracy, natural immunity may help the country avoid another horrific wave.
India may need to rely on natural immunity, as only 9% of its population is fully vaccinated, compared to just over 50% in the United States.
Britain has rolled out age-specific vaccines and 90% of adults have received at least one injection. The strategy produced benefits, limiting hospitalizations even when cases swelled. In the United States, vaccine distribution is more uneven – and the rise and fall of the delta will be, too, Hanage said.
“The nature of delta transmission means that cases will increase in many places around the same time, but the consequences will be much worse in terms of absolute numbers in places with less vaccination,” he said. .
Hanage warned that reopening schools and offices in the United States would increase cases. About 10 million adolescents nationwide are vaccinated, which could mitigate the impact of reopening schools in particular, and more children could be vaccinated this fall.
Schools have not proven to be hotbeds of infection in previous waves, but school districts now have fewer restrictions in place.
“A lot of schools across the country just aren’t taking it very seriously this year,” Gounder said. “So you will see the transmission of schools in the community. “
Americans should expect increases during Thanksgiving, Christmas and New Years, as they did last year, she added – though none have been as bad as winter latest.
“I don’t think we’re really going to get over it until next spring,” Gounder said.
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