scorecardresearch Skip to main content

Unintended consequence of COVID control measures — kids without immunity

The nearly two years of intense COVID-19 mitigation measures in school and daycare has shifted the advantage to the influenza and RSV viruses, for the moment.

LaRanda St. John's 6-week-old son, Beau, lies in a hospital bed with RSV at the Sarah Bush Lincoln Health Center in Matoon, Ill., in July 2021.LaRanda St. John/Associated Press

An early surge of respiratory syncytial virus — better known as RSV — is straining pediatric hospital resources across the United States. Other respiratory viruses are rampant as well. There’s a phrase often used by pediatricians and parents when discussing the infectious risks and benefits of daycare versus in-home care for pre-school age children: Pay now or pay later.

The reality is that respiratory viruses are inevitable, and while a child cared for at home may contract fewer viral infections during those early years than one who goes to daycare, the child who attended daycare will enter kindergarten with more immunity than the child cared for at home, because all children will be exposed to these viruses. It’s a question of when, not if.


In spring 2020, simultaneous with the message to stay at home to avoid COVID-19 infection, those of us working in health care saw a sudden and near-complete disappearance of other respiratory viruses (including flu and RSV) in our patients. But in summer 2021, RSV came back with a vengeance, and last winter, some areas saw a double-peaked, prolonged flu season that lasted until summer — a very atypical pattern. And now, even with substantial COVID-19 community transmission, we are seeing a simultaneous RSV surge and an early, rapidly escalating flu season, resulting in the coining of the term “tripledemic.”

The past two years have been undeniably weird for kids. Usual routines were interrupted by school closures, curtailed socialization, masks, and other behavioral changes that fundamentally altered their lives. Even in places with scarce masking and open schools, the “stay home when sick” mantra was followed more than ever before. Requirements for negative COVID tests to return to school, often coupled with testing delays, meant that sick kids were mostly kept out of school while they were infectious, whether from COVID-19 or something else.


Given all of the disruptions in normal routines — and resulting diminished exposures to respiratory viruses — we shouldn’t be surprised by the current situation. Typically, kids are exposed to respiratory viruses starting when they are very young (a pre-school aged child will have at least six colds, or viral syndromes, per year), and slowly, over time, develop an adaptive immune response that provides some protection against future infection.

Under normal circumstances, 80 percent of kids have had RSV at least once by the time they are 2. For many respiratory viruses, including RSV, immunity is partial and short-lived, but substantial enough to keep respiratory infections in an equilibrium.

Some news headlines have been using the phrase “immunity debt” to describe the current phenomenon, in which a lack of immunity caused by a period of reduction in exposure to viruses has led to a subsequent spike in respiratory illness. But this phrase has created some confusion — the change in immunity is happening at a population level, not an individual level. Immune systems are not weakened by a lack of exposure to viruses. Further, there is no clinical evidence that the increase in respiratory illness is caused by immune systems having been damaged in some way by COVID infection itself. Rather, children’s immune systems are working as they always have been — the major difference is that all of the disruptions to their lives have limited exposure and led to a dangerous unintended consequence: a large proportion of children whose immune systems haven’t been subjected to the typical childhood infections. More children are susceptible than usual, and all at the same time.


The nation undertook drastic measures to buy time to develop COVID-19 vaccines. These measures, it appears, may have disrupted what was a delicate balance between population immunity and viral infections. The nearly two years of intense mitigation measures in school and daycare and beyond in some regions has shifted the advantage to the viruses, for the moment. Although severe RSV disease affects mostly infants under the age of 6 months, who haven’t lived long enough to be affected by “immunity debt,” in a normal year they are partially protected by a combination of maternal antibodies acquired in utero and via breast milk, and by the immunity of the adults and older children around them. Not this year.

Strangely, it appears that flu and RSV disappeared in areas with open schools and no masking. This phenomenon may reflect the strong impact of adult behavior change, reduction in travel, and attention to hygiene, including hand washing. The fact is no one really understands the complex interplay of factors that has resulted in the phenomenon we see today.

The response to the surge in respiratory pathogens is to reopen discussions about mask mandates, mostly in schools, in an attempt to stem the tide. There are even reports of school closures. But the reality remains — we aren’t in a situation where “pay never” is a realistic option.


Measures we take now to prevent viral infections in kids may just kick the can down the road further. Humans are social creatures, children need to attend school, and a return to any sense of normalcy after creating population-wide “immunity debt” could come with a surge in cases. Some would argue that mask mandates never worked to stem the tide of COVID-19, so they couldn’t be contributing to “immunity debt” from other viruses. But whether or not masks in particular worked is, to some extent, an academic exercise. If they did, then “immunity debt” needs to be considered as a consequence of mask mandates. And if they didn’t, then they really aren’t warranted.

The good news is that the “immunity debt” is not permanent — once kids develop immunity, the advantage switches away from the viruses, and we should see equilibrium again. Point in fact: RSV cases have peaked and are on the way down despite the fact that no broad sweeping restrictions have been implemented. That’s population immunity at work. But add the current surge to the long list of reasons we need to entirely rethink our responses to respiratory virus threats.

Clearly, some combination of the strategies we used did stop non-COVID viruses in their tracks, and it appears we may now be seeing the impacts of those disruptions on normal viral epidemiologic patterns. Questions about short-term effectiveness of mitigation measures need to be weighed against the many long-term harms: learning loss, language delays, interrupted social development, economic consequences, loneliness, mental health exacerbations, and now, it seems, surges of respiratory viruses.


Perhaps we should add respiratory viruses to the list of things that are inevitable in life — like death and taxes — and adjust our expectations and policies accordingly. Staying home when sick is important, as is learning and socializing when healthy.

Dr. Shira Doron is an infectious disease physician and the hospital epidemiologist at Tufts Medical Center. She is an associate professor of medicine at Tufts University School of Medicine. Dr. Elissa Perkins is an associate professor of emergency medicine and the vice chair of emergency medicine research at Boston University School of Medicine/Boston Medical Center. Dr. Westyn Branch-Elliman is an associate professor of medicine at Harvard Medical School and an infectious diseases specialist. All three have served as unpaid advisers to the Massachusetts commissioner of education. Doron has served as an unpaid adviser to the governor.