What causes the COVID-19 surges?
The United States is not coping well with the current surge of COVID-19 infections. Coronavirus-related hospitalizations nationwide surpassed 100,000 last week for only the second time in the pandemic, overwhelming caregiver capacity in several states.
The worst situation is in intensive care units , which care for the sickest patients with highly specialized medical staff who are in short supply and are becoming progressively burned out as the pandemic drags on. The result is that in many parts of the country, patients needing to be hospitalized are being shuttled long distances to available beds and are receiving substandard care due to staffing shortages.
Given the abundance of readily available, free, effective (albeit imperfect) vaccines for many months, what is going on? There are three primary factors at work that dictate the severity of an outbreak of a viral illness.
The first is the profile of the virus, which itself has two variables: transmissibility and virulence, the severity of illness in people who become infected. The first of these is represented by a variable called R0, or R-naught. The delta variant of SARS-CoV-2, the virus that causes COVID-19, is now dominant in the U.S., and it is more than twice as infectious as the original Wuhan coronavirus and about 50% more infectious than the once-dominant alpha variant. That is important because it means that once relatively safe activities and casual contacts now have a higher probability of transmitting infection.
As to virulence, a large, just-published British study found “a higher hospital admission or emergency care attendance risk for patients with COVID-19 infected with the delta variant compared with the alpha variant.”
Thus, with delta, we have a virus that is both more transmissible and more virulent. Not surprisingly, then, outbreaks, especially in unvaccinated populations, are a much greater burden on healthcare systems than the alpha variant. Moreover, every COVID-19 infection involves the replication of the virus’s RNA, more mutations, and new opportunities for even more worrisome variants to emerge.
The second factor that determines the severity of an outbreak is the state of immunity of potential hosts, or victims, of the virus. The first line of defense is the “innate immune response ,” which consists of nonspecific physical, chemical, and cellular defenses against pathogens. The second line of defense is the adaptive, or acquired, immune response , which is mediated by white blood cells called lymphocytes, in response to a pathogen or to a vaccine that protects against that pathogen. Some lymphocytes produce specific anti-pathogen proteins called antibodies, while others attack the pathogen directly.
Only about 60% of the U.S. population is fully vaccinated, and on July 28, a study published as a preprint (that is, not yet peer-reviewed) showed that the Pfizer-BioNTech vaccine’s efficacy against symptomatic disease had slipped from 96% to 84% after six months. Such findings are spurring discussions about when vaccine booster doses will be needed and to whom they’ll be offered.
The third factor affecting outbreaks is the behavior of individuals and policymakers. Vaccination, whether voluntary or mandated, is our most potent weapon to suppress symptomatic infections and thereby “flatten the curves” of hospitalizations and deaths. “Non-pharmaceutical interventions,” such as masks, social distancing, avoidance of crowded indoor spaces, and good ventilation, are also effective. As illustrated by this figure , first conceived by Australian virologist Ian Mackay, the more NPIs (in conjunction with vaccines), the better.
A July incident in Marin County, California (one of the nation’s most-vaccinated locales), illustrates what can happen when people behave irresponsibly. Between May 23 and June 12, 26 laboratory-confirmed COVID-19 cases occurred in elementary school students and their contacts after they were exposed to an unvaccinated, infected, and symptomatic teacher who removed her mask to talk to the students. The infection rate in one affected classroom was 50%, and the risk of infection correlated with students’ seating proximity to the teacher.
Another example occurred in South Dakota, where COVID-19 cases spiked after the Sturgis Motorcycle Rally in August, when hundreds of thousands of bikers descended upon the area. Between Aug. 4, the date closest to the start of the rally for which data were available, and Aug. 25 (10 days following the end of the rally), the state reported an increase in active COVID-19 cases of 456%.
Finally, policymakers must carefully balance questions of freedom of movement and actions with public health considerations. Permitting superspreader events and bans of mask or vaccination mandates clearly impede control of the pandemic and prolong the misery and the proliferation of cases, hospitalizations, and deaths.
We have the tools to flatten the curve, and we need to use them.
Henry Miller, a physician and molecular biologist, was the co-discoverer of a critical enzyme in the influenza virus and the founding director of the FDA’s Office of Biotechnology.