Trying to understand the mysterious 2-month cycle of COVID

COVID-19 is on the decline again.

The reasons remain somewhat unclear and there is no guarantee that the decline in the number of cases will continue. But the turnaround is now big enough – and lasts long enough – to deserve attention.

The number of new daily cases in the United States has fallen 35% since September 1. Globally, cases have also fallen by more than 30% since the end of August. “It’s as good as the world has watched for many months,” wrote Dr Eric Topol of Scripps Research last week.

The most encouraging news is that the more severe forms of COVID are also on the decline. The number of Americans hospitalized with COVID has fallen by about 25% since September 1. Daily deaths – which typically change direction within weeks of cases and hospitalizations – have fallen 10% since September 20. This is the first sustained drop in deaths since the start of the summer.

These declines are consistent with a pattern readers will recognize: the mysterious two-month cycle of COVID. Since the COVID virus began to spread in late 2019, cases have often increased for around two months – sometimes due to a variant, such as delta – and then decreased for around two months.

Public health researchers do not understand why. Many popular explanations – such as seasonality or the ebb and flow of mask-wearing and social distancing – are clearly insufficient, if not false. The two-month cycle occurred during different seasons of the year and occurred even when human behavior was not obviously changing.

The most plausible explanations involve a combination of viral biology and social media. Perhaps each variant of the virus is particularly susceptible to infecting some people but not others – and once many of the most vulnerable have been exposed, the virus recedes. And maybe a variant takes about two months to circulate in a medium-sized community.

Human behavior plays a role, people often become more cautious once the number of cases starts to increase. But social distancing is not as important as the public debate about the virus often imagines. “We have attributed too much human authority to the virus,” Michael Osterholm, an infectious disease expert at the University of Minnesota, told me.

The recent declines, for example, came even as millions of American children once again crowded into school buildings.

Whatever the reasons, the two-month cycle continues to occur. This can be seen in the global figures: cases around the world rose from late February to late April, then declined until late June, rose again until late August, and has been declining since.

The pattern has also been evident in countries including India, Indonesia, Thailand, Britain, France and Spain. In each of them, the delta variant resulted in an increase in cases lasting from 1 1/2 to 2 1/2 months.

In the United States, the delta thrust began in several southern states in June and began to recede in those states in August. In much of the rest of the United States, it started in July and cases have started to decline in recent weeks. Even pediatric cases are on the decline, despite the lack of vaccination clearance for children under 12, as Jennifer Nuzzo of Johns Hopkins University told the Washington Post.

I want to stress that these declines may not persist. The two-month cycle of COVID is not some iron law of science. There were a lot of exceptions.

In Britain, for example, the number of cases has fluctuated over the past two months, rather than steadily declining. In the United States, the onset of cold weather and increased indoor activities – or another unknown factor – could potentially trigger an increase in cases this fall. The evolution of the pandemic remains very uncertain.

But this uncertainty also means that the near future could also turn out more encouraging than expected. And there are legitimate reasons to be optimistic about COVID.

The share of Americans aged 12 and over who have received at least one vaccine injection has reached 76%, and the growing number of vaccination mandates – as well as the probable approval of the Pfizer vaccine for children ages 5 to 11 years – will increase the number of vaccines this fall. Almost as important, something like half of Americans have probably had the COVID virus before, which gives them natural immunity.

Eventually, immunity will become widespread enough that another wave as large and damaging as the delta wave is not possible. “Except for something unexpected,” said Dr. Scott Gottleib, former Commissioner of the Food and Drug Administration and author of “Uncontroled Spread,” a new book on COVID, “I am of the opinion that this is of the last great wave of infection. “

COVID has not only been one of the worst pandemics of modern times. It has been an unnecessarily terrible pandemic. Of the more than 700,000 Americans who have died from it, nearly 200,000 could probably have been saved had they chosen to be vaccinated. It is a national tragedy.

COVID isn’t going away anytime soon, either. It will continue to circulate for years to come, many scientists believe. But vaccines can turn COVID into a manageable illness, not all that different from the flu or a cold. In recent weeks, the country seems to have moved closer to that less bleak future.

Whatever happens in the next few months, the worst of the pandemic is almost certainly behind us.