Lagging or Leading Indicators?

At the end of January the seven-day US national average for covid deaths was still over 3000 per day (down from more than 4000 in mid-January). As of February 21, the average daily death count was under 2000 and falling. Hospitalizations have declined by more than 50 percent since early January.

Some have credibly suggested that given our high incidence of disease and related death that the US could be approaching herd immunity. With more than 500,000 confirmed deaths, the United States has one of the highest per capita death rates and related pandemic disease profiles on the planet.

Given an almost year-long burnt-earth (prairie fire?) strategy — sometimes intentional , sometimes not —  I concur that, first, the United States has had many more mild covid cases than confirmed by our anemic testing capacity and, second, this has reduced the proportion of non-infected persons available to facilitate virus transmission. As a result, there are now some inherent transmission curbs and guard-rails that were not in place one year ago. Vaccinations are adding more, even stronger Jersey barriers.

It is also interesting that since Halloween mask-use in the United States has increased from about 70 percent of the population to about 80 percent of the population. Since late October cellphone data suggest that US residents have noticeably reduced our circulation. Over most of the autumn we had reduced circulation by between one-fifth and one-quarter of typical. But since Thanksgiving we have reduced our circulation by closer to one-third. There are some significant regional differences, but I am — pleasantly — surprised. Less traffic, less opportunity for viral velocity.

Even more surprising, in some places where more contagious variants are prevalent, hospitalizations and fatalities have also started to decline.  Late January peaks in the United Kingdom and South Africa have fallen fast. During this same period, British mobility has been reduced by half. For a few weeks South Africa reduced mobility by over 35 percent.  South Africans allegedly use face coverings more than Americans. The Brits use face coverings a bit less. The health data in Brazil is much more treacherous and both mobility-reduction and mask use are anemic. Human circulation is clearly very influential in virus circulation.

One more comparison: When case counts began spiking in Denmark the government reacted quickly (more). Only about twenty percent of Danes practice masking, but there is rigorous testing, tracing, and public health interventions to contain outbreaks. When the more contagious B117 variant began surging, public actions and private cooperation reduced observed cell phone mobility from a meager 17-percent-of-typical in early December to a 56-percent-reduction by the end of December.  Hospitalization and death rates began dropping in response. Still, and worth emphasizing, the variant continues to find ways to infect an increasing proportion of the population.

Uncertainty has often been the most honest response to the coronavirus. There is, however, plenty of evidence that when more of us spend more time inside in close proximity to each other, the virus finds a way to use this against us.  This is apparently what recently happened at the University of Virginia (more).  This will continue to be a very real risk for at least several more months. When there is much we do not know, it is usually prudent to behave cautiously in accordance with what we do know.

UPDATE: On February 25, the Financial Times reported on these issues, concluding, “Despite recent success in tackling the virus, scientists emphasised that all countries remained vulnerable to surges in new cases. “Any rapid relaxation of protective measures could produce spikes in infection rates,” said Ted Cohen, professor of infectious disease epidemiology at Yale University. “There are large pools of susceptible individuals still at risk.”