Opinion: Why we can't let our guard down in fight against the coronavirus

Governors are being pressured to relax measures that curb the spread of COVID-19. To make informed policy decisions, the consequences of these measures need to be fully considered. One effect that has been overlooked is the response of the virus itself. Our actions against the agents of disease often change them. Use of antibiotics generates antibiotic resistance. Vaccines and control of transmission can make targeted pathogens less dangerous or more so.

Thanks to Gov. Andy Beshear’s guidelines, the high-risk hard work of health care workers and the diligence of Kentuckians in following coronavirus restrictions, deaths in Kentucky, though tragic, have been relatively few.

To fully understand how to control COVID-19 now and in the future, we must first consider viral durability in the external environment. Coronaviruses are moderately durable — they typically persist for a few days, though they sometimes can last for more than a week. Viruses with this persistence typically equilibrate at a level of harmfulness that causes about one death in 1,000 infected people. Death rates during the early phase of the pandemic are hard to come by because they fail to account for the total number of people infected. 

One of the best measurements can be calculated from the people on the Diamond Princess cruise ship. Of the 712 people infected on the ship 1.8% have now died. After accounting for the older age of cruise passengers, this mortality translates to about 1% for the general population, about 10 times the lethality that we would expect after the virus adapts to humans. 

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Durable viruses can be transmitted effectively from very sick people because uninfected people can be exposed to the virus in contaminated sites. The protective actions enacted in Kentucky limit this route of transmission and therefore could contribute to a shift of the virus toward a less damaging relationship with humans. Social distancing, disinfection, staying at home when sick, restricting the sizes of gatherings, and increasing protection in hospitals and residences for the elderly take away the advantages that harmful durable viruses have over milder viruses. On the basis of these consideration we expect that the COVID-19 viruses will shift toward a level of harmfulness that is below the one death per thousand where strong infection control measures are maintained.

Like Beshear, California’s Gov. Newsom put in place strong control measures early during the pandemic. Although the reliability of antibody tests are still being debated, broad immunological testing for infections in a northern California county indicate that as of early April about one death occurred per 1,000 infections, a finding that is consistent with the idea that the COVID-19 viruses circulating there may have already shifted substantially toward lower harmfulness. Scientific research together with increased immunological testing for unnoticed infections should soon reveal whether the virus is shifting toward mildness. 

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Because states and countries differ greatly in their use of these options for control of COVID-19, we are beginning to witness epidemiological effects of strong infection control. Consider Sweden and Norway. Sweden has put in minimal protective restrictions in response to the COVID-19 outbreak, has about twice the population of Kentucky, and currently has over 10 times the number of deaths from the virus. Neighboring Norway has implemented COVID-19 measures similar to those of Kentucky. It has roughly the same population as Kentucky and number of COVID-19 deaths. These comparisons indicate that vigilant efforts against COVID-19 transmission reduce deaths by about 80%.

The printed federal guidelines for opening the economy, emphasize the importance of broader testing. With more complete testing we should be able to assess whether Kentucky will achieve progressively lower numbers of deaths per infection as the pandemic proceeds. Real declines in deaths per infection will be good news for the outlook of the pandemic during the summer and beyond. Relaxing vigilance could compromise these benefits.

By flattening the curve, control measures enacted in Kentucky have prevented needless deaths due to an overwhelmed health care system and shifted some infections to later weeks. If the virus is steadily becoming less harmful, then delaying infections may be especially important for individuals who have had inadequate health care opportunities. For example, in Kentucky and throughout the U.S., African Americans are disproportionately represented among COVID-19 cases and deaths. Being infected with milder variants of COVID-19 could be the difference between life and death for individuals whose infections are worsened by inequality of health care and preexisting conditions. As Beshear has repeatedly emphasized, protection from COVID-19 will require not only controlling the virus but also addressing the disparities that make large numbers of Americans especially vulnerable. We can rise to this multifaceted challenge.

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Paul W. Ewald and Holly A. Swain Ewald are professors in the University of Louisville's Department of Biology.