Mask use and social distancing considerably reduce the incidence of many diseases, including COVID-19

Reviewed by Emily Henderson, B.Sc.November 10, 2020

Measures to reduce the spread of COVID-19 through non-pharmaceutical interventions (NPIs) such as mask donning and social distancing are a key tool to combat the impact of the ongoing coronavirus pandemic.

These actions have also greatly reduced the incidence of many other diseases, including influenza and respiratory syncytial virus (RSV).

The current reductions in these common respiratory infections, however, could simply postpone the incidence of future outbreaks, according to a study by Princeton University researchers published Nov. 9 in Proceedings of the National Academy of Sciences.

“There has been a recent decline in the number of different respiratory pathogens in many locations around the world,” said lead author Rachel Baker, an associate researcher at Princeton University’s High Meadows Environmental Institute (HMEI).

“While this reduction in cases could be interpreted as a positive side effect of preventing COVID-19, the reality is much more complex,” Baker said. “Our results suggest that susceptibility to these other diseases, such as RSV and influenza, could increase while NPIs are in place, causing major outbreaks when they begin to circulate again.”

Baker and his co-authors found that NPIs could lead to a future increase in RSV – a viral infection endemic in the United States and a leading cause of lower respiratory tract infections in young children – but that the same effect was not as pronounced for the flu.

Although the detailed trajectory of RSV and influenza over the next few years will be complex, there are clear and general trends that emerge when focusing on some essential effects of NPIs and seasonality on disease dynamics.. “

Gabriel Vecchi, study co-author and professor, Geosciences, High Meadows Environmental Institute, Princeton University

Researchers used an epidemiological model based on historical RSV data and observations of the recent decline in RSV cases to examine the possible impact of COVID-19 NPIs on future RSV outbreaks in the United States and Mexico.

They found that even relatively short periods of NPI measures could lead to large future outbreaks of RSV. These outbreaks were often delayed after the end of the NPI period, with peak cases expected in many locations in the winter of 2021-22.

“It is very important to prepare for this possible future epidemic risk and pay attention to the full range of infections affected by COVID-19 NPIs,” Baker said.

The authors also considered the implications of COVID-19 NPIs for seasonal influenza outbreaks and found results that were qualitatively similar to RSV. The dynamics of influenza are much more difficult to project due to viral evolution, however, which drives uncertainty about future circulating strains and the efficacy of available vaccines.

“For the flu, vaccines could make a big difference,” Baker said. “Furthermore, the impact of NPIs on influenza evolution is unclear but potentially very important.”

“The decline in influenza and RSV cases – as well as the possible future increase we anticipate – is probably the largest global impact of NPIs on a variety of human diseases that we have seen,” said co-author Bryan Grenfell, Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary Biology and Public Affairs, who is an associate professor at HMEI.

“NPIs could have unintended long-term impacts on the dynamics of other diseases that are similar to the susceptibility impact we have predicted for RSV,” he said.

A similar effect of pandemic-related NPIs on other pathogens was observed after the 1918 flu pandemic. London’s historical measles data show a shift from annual cycles to biennial outbreaks following a period of control measures implemented at that time .

Co-author C. Jessica Metcalf, associate professor of ecology and evolutionary biology and public affairs and associate faculty member of HMEI, said that directly assessing the associated risks of NPIs by developing and implementing tools such as serology that would better measure susceptibility is a important public health and political direction.

“The future repercussions of NPIs revealed by this paper depend on how these measures change the landscape of immunity and susceptibility,” Metcalf said.