Death rates from the novel coronavirus are lower in hot spots around the world, even as new infections accelerate in what may be the pandemic’s next wave. Scientists are confident the change is real, but the reasons for it — and whether it will last — are a matter of intense debate.

Public health officials cite multiple reasons for the lower death rates: They note a shift in the demographics of who is being stricken with the virus, with younger people making up the bulk of new infections. More widespread testing is capturing a more diverse range of people and illness, and improved treatment strategies that include antivirals and steroids are saving more lives. But some researchers speculate there may be more to the story.

One idea that has generated a lot of discussion recently, bolstered by two back-to-back studies — one by Said El Zein of the Detroit Medical Center, and another from Italy, presented in late September to the European Society of Clinical Microbiology and Infectious Diseases — is that social distancing and masks are reducing the dose of virus people are receiving, resulting in less-severe illness.

As El Zein and other doctors in Detroit probed why their patients appeared to be less ill, they were startled to find that one indicator in particular changed dramatically over time: viral load.

Among 708 patients treated by early summer, the average viral load — a measure of the particles of virus in the body as measured by nasal swabs — fell almost on a weekly basis. In most infectious diseases, including Ebola, HIV/AIDS and hepatitis, the higher the load, the worse the outcome.

El Zein saw glimmers of hope in the findings: Could it be that the steps being taken to mitigate the coronavirus’s effects were showing success?

Monica Gandhi, an infectious-diseases researcher at the University of California at San Francisco, shares that view. If the initial viral dose — known as the “inoculum” — is lower, she theorized, people’s bodies are able to fight back more effectively.

This “likely indicates an ability to control the viral infection better, and, therefore, have less severe disease,” Gandhi said.

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