Why the US is seeing a Covid-19 plateau

WASHINGTON • When epidemiologists talked about "flattening the curve", they probably did not mean it this way: the United States hit its peak coronavirus caseload in April, but since then the graph has been on a seemingly unending plateau.

That is unlike the situation in several other hard-hit countries which have successfully pushed down their numbers of new cases, including Spain and Italy, which now have bell-shaped curves.

Experts say the prolonged nature of the US epidemic is the result of the cumulative impact of regional outbreaks, as the virus that started out primarily on the coasts and in major cities moves inwards.

Layered on top of that are the effects of lifting lockdowns in parts of the country that are experiencing a rise in Covid-19 cases, as well as a lapse in compliance with social distancing guidelines because of economic hardship and, in some cases, a belief that the threat is overstated.

"The US is a large country both in geography and population, and the virus is at very different stages in different parts of the country," said Dr Tom Frieden, a former director of the Centres for Disease Control and Prevention.

The US saw more than 35,000 new cases for several days in April. While that figure has declined, it has still been exceeding 20,000 regularly in recent days.

In terms of fatalities, University of Washington researchers estimated on Monday that 145,728 people could die of Covid-19 in the US by August, raising their grim forecast by more than 5,000 deaths in a matter of days.

Last Friday, the Institute for Health Metrics and evaluation at the university projected 140,496 deaths by August from Covid-19. Researchers did not give a reason for the abrupt revision.

The new estimate came on the same day Texas reported its highest number of hospitalisations so far in the outbreak and a total of 22 US states showed an uptick in the number of new confirmed cases, according to a count kept by Johns Hopkins University.

By contrast, Italy was regularly hitting over 5,000 cases per day in March but is currently experiencing figures in the low hundreds.

"We did not act quickly and robustly enough to stop the virus spreading initially, and data indicates it travelled from initial hot spots along major transport routes into other urban and rural areas," added Dr Frieden, now chief executive of the non-profit Resolve to Save Lives.

The East Coast states of New York, New Jersey and Massachusetts accounted for about 50 per cent of all cases until about a month or so ago, but the geographic footprint of the US epidemic has shifted to the Midwest and south-east, including Florida.

Another key problem, said Dr Jennifer Nuzzo, an epidemiologist at Johns Hopkins, is that the US is still not doing enough testing, contact tracing and isolation.

After starting late on testing - for reasons ranging from technical issues to regulatory hurdles - the US has now conducted more Covid-19 tests than any other country. It even has one of the highest per capita rates of 62 per 1,000 people, according to the website ourworldindata.org - better than Germany (52 per 1,000) and South Korea (20 per 1,000).

But according to Dr Nuzzo, these numbers are misleading because "the amount of testing that a country should do should be scaled to the size of its epidemic".

She added: "The US has the largest epidemic in the world so obviously we need to do a lot more testing than any other country."

For Johns Hopkins, the more important metric is the positivity rate - that is, out of all tests conducted, how many came back positive for Covid-19. As of Sunday, the US had an average daily positivity rate of 14 per cent, well above the World Health Organisation guideline of 5 per cent over two weeks before social distancing guidelines should be relaxed.


A version of this article appeared in the print edition of The Straits Times on June 10, 2020, with the headline 'Why the US is seeing a Covid-19 plateau'. Print Edition | Subscribe