The novel coronavirus may one day become a seasonal virus like the flu — but that day won’t come until herd immunity is achieved, according to the findings of a recent review published in Frontiers in Public Health.
SARS-CoV-2, the virus that causes the COVID-19 infection, will likely become seasonal “in countries with temperate climates” following herd immunity, according to a press release on the study’s findings. But until then, study authors said the novel virus will “continue to circulate across the seasons.”
"COVID-19 is here to stay and it will continue to cause outbreaks year-round until herd immunity is achieved. Therefore, the public will need to learn to live with it and continue practicing the best prevention measures, including wearing of masks, physical distancing, hand hygiene and avoidance of gatherings,” said Dr. Hassan Zaraket, of the American University of Beirut in Lebanon and senior author of the study, in a statement.
There are at least four pre-existing coronaviruses that are seasonal — but why exactly they are remain somewhat shrouded in mystery. For instance, the 2002-2003 outbreak of severe acute respiratory syndrome (SARS), which claimed nearly 800 lives at the time, ended in the summer — but a 2004 report on the seasonality of SARS did not establish a clear reason for why that was.
“Our understanding of the forces driving seasonal disappearance and recurrence of infectious diseases remains fragmentary, thus limiting any predictions about whether, or when, SARS will recur,” the authors wrote at the time. “It is true that most established respiratory pathogens of human beings recur in wintertime, but a new appreciation for the high burden of disease in tropical areas reinforces questions about explanations resting solely on cold air or low humidity.”
For the new study, researchers reviewed seasonal viruses, namely the flu and several types of common cold-causing coronaviruses. They examined “the viral and host factors that control their seasonality as well as the latest knowledge on the stability and transmission of SARS-CoV-2,” per the release.
There is an ongoing debate within the scientific community about why some respiratory viruses are seasonal. Some factors that could contribute to seasonality may involve cold temperatures and lower humidity levels, allowing the virus to linger in the air and surfaces for longer periods of time.
“People's susceptibility to infections and human behaviors, such as indoor crowding, differ across the seasons due to changes in temperature and humidity. These factors influence [the] transmission of respiratory viruses at different times of the year,” the study authors added.
But at this moment, COVID-19 is not like other respiratory viruses, namely due to its higher rate of transmission (R0) which is “at least partly due to circulation in a largely immunologically naïve population.”
“This means that unlike the flu and other respiratory viruses, the factors governing seasonality of viruses cannot yet halt the spread of COVID-19 in the summer months. But, once herd immunity is attained through natural infections and vaccinations, the R0 should drop substantially, making the virus more susceptible to seasonal factors,” the researchers concluded, per the release.
The researchers’ findings echo one expert’s comments who told Fox News in June why the warm summer months were unlikely to kill off the virus.
“This virus has a high transmission rate so even in conditions that aren't as favorable, it's still going to spread,” Dr. John Whyte, the chief medical officer of the health care website WebMD, said at the time, noting that continued spread is “often dependent on mitigation factors.”
"This remains a novel virus and despite the fast-growing body of science about it, there are still things that are unknown. Whether our predictions hold true or not remains to be seen in the future. But we think it's highly likely, given what we know so far, COVID-19 will eventually become seasonal, like other coronaviruses," Zaraket said in the study release.
In the meantime, the study authors urged for “rigorous control measures to limit virus spread” until herd immunity is attained.