Figuring out which pandemic safety measures were prudent and which were misguided is the monumental project left to scientists, ethicists, public-health experts, and others now that (roughly) normal life has resumed. Among the most important but controversial subjects for reassessment are the COVID-19 interventions that affected children, including their ability to go to school or otherwise participate in basic social activities. In large portions of the United States, schools were closed for many months or even more than a year, activities for young people were broadly canceled, and tens of millions of American children were kept inside their homes and away from peers, teachers, relatives, and friends. While the persistent and considerable consequences of those policies are still coming to light, the main justification for them was that exposure to children increased COVID risk for adults.
A pair of new findings casts serious doubt on that logic. The two studies were published in the journal Proceedings of the National Academy of Sciences — one in August and one last month — and together they achieved something rare: They offered dramatic and important new information suggesting a correction to a commonly held narrative about children as dangerous viral vectors during the pandemic. But their results, according to multiple experts interviewed for this article, were also entirely expected.
The August paper found that “exposure to young children was strongly associated with less severe COVID-19 illness.” In an analysis of the records of more than 3 million adults in the Kaiser Permanente Northern California health system, the authors found that “those without identifiable household exposure to children based on health insurance enrollment had a 27% higher rate of COVID-19 hospitalization and a 49% higher rate of COVID-19 hospitalization requiring ICU admission than those with young children.” (In comparing adults with and without exposure to young children, the analysis matched each group for known COVID risk factors such as age, hypertension, diabetes, and BMI.) The study’s researchers, from Kaiser, Stanford University, and Columbia University, said their findings suggest that cross-immunity from common coronaviruses — which sometimes cause the colds and sniffles that children tend to carry — may play a role in protection against severe COVID-19 outcomes.
The study published in November, by researchers from Harvard Medical School, Boston University School of Medicine, and the Veterans Administration, offered biological evidence for the Kaiser study’s epidemiological finding. The researchers found that, during the first year of the pandemic, VA patients who had tested positive for some of the common-cold coronaviruses had an 80 to 90 percent reduction in likelihood of testing positive for SARS-CoV-2 infection. In other words, at least for a limited time, getting the common cold appeared to help some people’s immune system protect against COVID.
These two studies — one relying on laboratory data, the other on observational data — complement each other so compellingly that the researchers behind the November study cite the August paper as the inspiration for theirs. Taken together, the findings suggest that social distancing and isolation at a population level, particularly from young children, may have counterintuitively put some people at greater risk of COVID infection or severe disease once they resumed normal contact. (Several of the experts I spoke with noted that this doesn’t mean social distancing wasn’t beneficial for those at high risk of bad outcomes who were able to remain uninfected until they were vaccinated.)
Francois Balloux, director of the Genetics Institute at University College London, whose work focuses on the epidemiology of infectious diseases, said cross-protection — that is, exposure to the common-cold coronaviruses triggering greater immune protection against COVID — had long been the subject of quiet speculation by experts. “This hypothesis was aired since the beginning of the pandemic but was viewed as dangerous,” he said. “People avoided talking about this in polite circles.”
But the public discussion now seems to be happening. For instance, a recent essay in the New York Times on the relative absence then reemergence of certain viruses, co-authored by a virologist and an infectious-diseases epidemiologist, noted the possible effects of social distancing as well as cross-reactivity (infection from one virus conferring an immune-system benefit against other viruses) in this process.
The VA study adds intriguing new data to this conversation. There are four endemic coronaviruses that can cause the common cold. The VA researchers found that people who had tested positive within the past year for two them — either 229E or OC43 — had a significantly lower rate of COVID than patients who had not tested positive for either of these coronaviruses.
Dr. Jake Scott, an infectious-diseases specialist at Stanford University, said the VA study had some significant limitations, but its findings fit with the existing literature, which indicates “there’s good reason to believe exposure to human coronavirus can lead to some degree of cross-immunity to SARS-CoV-2.”
The evidence of cross-protection should cause people to question some commonly held assumptions that governed pandemic safety measures. Balloux, who is a co-author on a study published last year in the journal Nature exploring how exposure to endemic coronaviruses might help T-cell immunity to SARS-CoV-2 infection, said the VA paper was just the latest small addition to the literature on the broader topic. And overall, Balloux said, it supports the idea that, at a population level, teachers or other professionals with exposure to young children were not at greater risk, as was the conventional wisdom during the pandemic, which drove policy decisions about shuttering schools and children’s activities.
This protective concept exists beyond the endemic coronaviruses. Although Scott did not want to apply this lesson to any policy decisions around mitigations, he said, “the infectious diseases that kids often spread are usually benign and can provide adults with certain immunological protection that they might not otherwise think about.”
To whatever extent school closures or social distancing from children reduce transmission, there may be a downside to those aggressive mitigations, said Dr. Paul Monach, one of the VA study’s authors. “It’s been proposed that the current surge of RSV may in part be because our population didn’t get it for two years,” he said. “It’s plausible that we can overprotect ourselves from viruses.” Instead, “getting a mini- or even micro-booster periodically simply by going about your life would be very reassuring.” He warned, though, that doing so is tricky and depends on how dangerous the virus is to children and everyone else.
While no one enjoys getting colds, these studies suggest that exposure to young children and their colds may offer a protective benefit against more serious illness. Dr. Monica Gandhi, an infectious-diseases specialist at University of California, San Francisco, said that, in light of the protective benefit of mild coronaviruses, “we need to evaluate unintended consequences” of preventing that exposure.