Intermittent social distancing may be necessary for years to slow the spread of COVID-19 and ensure patients with the virus don’t overwhelm hospitals, according to a new report out of Harvard University.

Such measures would be needed in the absence of a vaccine or other effective treatments, researchers say.

The report compared COVID-19 to two coronaviruses that circulate regularly in humans in the fall and winter — OC43 and HKU1 — and projected that COVID-19 could come back after the pandemic and circulate in the same way.

As a result, “intermittent” social distancing measures may be needed into 2022 in order to avoid overwhelming the health-care system if there is a resurgence of the disease, the report found.

“One-time social distancing measures are likely to be insufficient” in maintaining the spread of COVID-19 within the community, said Stephen Kissler, a post-doctoral fellow with Harvard T.H. Chan School of Public Health and co-author of the report.

“What seems could be necessary in the absence of other sorts of treatments are intermittent social distancing periods to maintain the number of critical cases” of COVID-19 and prevent an overburdened health-care system, Kissler said.

The HKU1 and OC43 viruses are two of four coronaviruses endemic to humans that are responsible for an estimated one-quarter of all colds, according to news reports. The other two coronaviruses are NL63 and 229E.

The report focused on HKU1 and OC43 because they’re in the same family as COVID-19, said Christine Tedijanto, a co-author of the report, at a press conference Tuesday.

The viruses prefer cool and dry conditions and don’t thrive as well in heat and humidity.

“We used data on (HKU1 and OC43) to characterize … duration of immunity and cross immunity in order to inform our model for” COVID-19, said Tedijanto.

“What we see with these two betacoronaviruses that we focus on” in the report is that they “display clear seasonal patterns,” with incidents peaking around December and January, said Tedijanto.

The modelling shows the betacoronaviruses were more transmissible in fall and winter, with transmissibility dropping off as spring arrived. In all of the scenarios the researchers looked at, COVID-19 appeared to be able to spread year-round, though worse outbreaks would be likely in fall and winter.

The report’s models did not take into account additional prevention measures, such as treatments or the creation of a vaccine, which will “reduce the duration and intensity of social distancing required to maintain control of the epidemic,” co-author Yonatan Grad said. These interventions could alter the outcome of the report’s findings.

Already, scientists at Oxford University are working on a vaccine and recruiting volunteers for the first clinical trial in the Thames Valley area, outside London. The vaccine is in production although it won’t be ready for some weeks, according to the university’s website.

The report from Harvard notes that additional interventions, such as expanding the capacity of critical-care units would “improve the success of intermittent distancing and hasten the acquisition of herd immunity,” which occurs when a high enough proportion of people are immune that the virus fails to spread.

The extent of population immunity to the virus will be “very valuable” to understand what will happen with COVID-19 in coming years, Grad said. He stressed that widespread testing for the virus will be key to monitoring when the beginning or end of social distancing should take place.

Up to this point, intensive care units in Ontario hospitals have not been overwhelmed, which may point to the success of social distancing efforts, although there is no definitive research out yet. Canadians have been adhering to social distancing rules, according to a study released Tuesday by York University, which found 96 per cent of respondents reported limited social engagements.

An expert who weighed in on the Harvard study praised the researchers but said that with so much unknown about COVID-19, it was difficult to predict if the virus would behave similarly to the two common cold viruses in the study.

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“This is an excellent study that uses mathematical models to explore the dynamics of COVID-19 over a period of several years, in contrast to previously published studies that have focused on the coming weeks or months,” said Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh.

“It is consistent with current (data) but is nonetheless based on a series of assumptions ... that are yet to be confirmed. The study should therefore be regarded as suggesting possible scenarios rather than making firm predictions.”

Another researcher, professor Gordon Dougan at the University of Cambridge’s department of medicine, praised the team but said, “I am not sure comparing with other coronaviruses is helpful, as SARS-CoV-2 (COVID-19) is much more pathogenic and invasive. However, overall there is little to compare SARS-CoV-2 with.”