Large, delayed outbreaks of endemic diseases possible following COVID-19 controls
Princeton
University
Measures
to reduce the spread of COVID-19 through non-pharmaceutical interventions
(NPIs) such as mask wearing and social distancing are a key tool in combating the impact of the ongoing coronavirus pandemic. And get your flu shot
These actions also have greatly reduced incidence of many other diseases, including influenza and respiratory syncytial virus (RSV).
Current
reductions in these common respiratory infections, however, may merely postpone
the incidence of future outbreaks, according to a study by Princeton University
researchers published Nov. 9 in the Proceedings of the National Academy
of Sciences.
"Declines in case numbers of several respiratory pathogens have been observed recently in many global locations," said first author Rachel Baker, an associate research scholar at the High Meadows Environmental Institute (HMEI) at Princeton University.
"While
this reduction in cases could be interpreted as a positive side effect of
COVID-19 prevention, the reality is much more complex," Baker said.
"Our results suggest that susceptibility to these other diseases, such as
RSV and flu, could increase while NPIs are in place, resulting in large
outbreaks when they begin circulating again."
Baker
and her co-authors found that NPIs could lead to a future uptick in RSV -- an
endemic viral infection in the United States and a leading cause of lower
respiratory-tract infections in young infants -- but that the same effect was
not as pronounced for influenza.
"Although
the detailed trajectory of both RSV and influenza in the coming years will be
complex, there are clear and overarching trends that emerge when one focuses on
some essential effects of NPIs and seasonality on disease dynamics," said
co-author Gabriel Vecchi, Princeton professor of geosciences and the High
Meadows Environmental Institute.
The
researchers used an epidemiological model based on historic 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 RSV outbreaks. These outbreaks were often delayed following the end of
the NPI period, with peak cases projected to occur in many locations in winter
2021-22. "It is very important to prepare for this possible future
outbreak risk and to pay attention to the full gamut of infections impacted by
COVID-19 NPIs," Baker said.
The
authors also considered the implications of COVID-19 NPIs for seasonal
influenza outbreaks and found results qualitatively similar to RSV. The
dynamics of influenza are much harder to project due to viral evolution,
however, which drives uncertainty over future circulating strains and the
efficacy of available vaccines.
"For
influenza, vaccines could make a big difference," Baker said. "In
addition, the impact of NPIs on influenza evolution is unclear but potentially
very important."
"The
decrease in cases of influenza and RSV -- as well as the possible future
increase we project -- is arguably the broadest global impact of NPIs across a
variety of human diseases that we've seen," said co-author Bryan Grenfell,
the Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary
Biology and Public Affairs, who is associated faculty in HMEI.
"NPIs
could have unintended longer-term impacts on the dynamics of other diseases
that are similar to the impact on susceptibility we projected for RSV," he
said.
A
similar effect of pandemic-related NPIs on other pathogens was observed
following the 1918 influenza pandemic. Historic measles data from London 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 an associated faculty member in HMEI, said that directly
evaluating the associated risks of NPIs by developing and deploying tools such
as serology that would better measure susceptibility is an important public
health and policy direction. "The future repercussions of NPIs revealed by
this paper hinge on how these measures change the landscape of immunity and
susceptibility," Metcalf said.
Additional
authors on the paper include Wenchang Yang, an associate research scholar in
geosciences, and Sang Woo Park, a Ph.D. candidate in ecology and evolutionary
biology.
Many
of the authors are affiliated with the Climate Change and Infectious Disease
initiative funded by HMEI and the Princeton Institute for International and
Regional Studies (PIIRS). The current study built on work by the same team
published in December 2019 that examined how climate conditions affect RSV
outbreaks in the US and Mexico. Another study by the team, published earlier
this year, evaluated the impact of the climate and susceptibility on the
trajectory of the COVID-19 pandemic.
The
paper, "The impact of COVID-19 non-pharmaceutical interventions on the
future dynamics of endemic infections" was published online Nov. 9 by
the Proceedings of the National Academy of Sciences. This work was
supported by the Cooperative Institute for Modeling the Earth System (CIMES),
the High Meadows Environmental Institute, and the Princeton Institute for
International and Regional Studies (PIIRS).