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Investigators found once some of the nonpharmacological interventions were relaxed some viruses returned to historical average case rates.
The byproduct of all the interventions put in place to combat the spread of COVID-19 may have had a profound impact on the rates of other viruses like influenza, at least initially.
A team, led by Zhong-Jie Li, Division of Infectious Disease, Key Laboratory of Surveillance and Early-warning on Infectious Disease, Chinese Center for Disease Control and Prevention, assessed the changes in respiratory infections in China during the first COVID-19 pandemic years compared to pre-pandemic years.
When the COVID-19 pandemic began, virtually every country implemented some nonpharmaceutical interventions (NPI), which could have a secondary impact on other acute respiratory infections.
The investigators identified 142,559 cases of acute respiratory infections between 2012-2021 using etiologically diagnostic data. The viral pathogens included influenza virus, respiratory syncytial virus (RSV) human parainfluenza virus (HPIV), human adenovirus, human metapneumovirus, human coronavirus, human bocavirus, and human rhinovirus (HRV).
Overall, test positive rates decreased in 2020 compared to average levels between 2012-2019, with influenza virus rates seeing the biggest decrease in 2020, an 87.6% drop in comparison to the pre-pandemic years.
On the other hand, the virus with the smallest decrease during the pandemic was RSV, which decreased 17.2% in 2020 compared to the 2012-2019 average.
The biggest decreases within the calendar year occurred between February and August when there were more nonpharmacological interventions in place. However, HRV increased to about historical levels during the summer, while RSV, HPIV, human coronavirus, HRV, and human bocavirus went beyond historical levels between September 2020 and January 2021 when the nonpharmacological interventions were largely relaxed and schools reopened.
Influenzas and human metapneumovirus were largely suppressed throughout the year.
Children and individuals in Northern China also saw the largest resurgence in acute respiratory viruses once the nonpharmacological interventions were relaxed. The observations still were valid, even after accounting for seasonality and long-term trend for each virus.
“Activities of respiratory viral infections were reduced substantially in the early phases of the COVID-19 pandemic, and massive NPIs were likely the main driver,” the authors wrote. “Lifting of NPIs can lead to resurgence of viral infections, particularly in children.”
Earlier this year, investigators from the University of California, Davis, found similar drops in respiratory viruses because of the COVID-19 restrictions in place.
There was a total of 46,128 tests for viral respiratory pathogens over the six-year study, 168 of which occurred during the postexposure period of March 25-July 31, 2020. There was a positive rate of 9.88 positive results per 100 tests during this period, significantly lower than the positivity rate of 29.90 positive results per 100 tests observed for the same date range during the previous 5 virus years.
In addition, the investigators found the positivity rates were similar for the preexposure time frame of August 1, 2019-March 24, 2020 and for the same time periods in the 5 previous years (30.40 vs. 33.68 positive results per 100 tests).
After performing a regression analysis, the investigators found statically significant decreases in viral activity in the postexposure period (93% decrease; incidence rate ratio [IRR], 0.07; 95% CI, 0.02-0.33) and for rhinovirus or enterovirus (81% decrease; IRR, 0.19; 95% CI, 0.09-0.39) infections.
The study, “Broad impacts of COVID-19 pandemic on acute respiratory infections in China: an observational study,” was published online in Clinical Infectious Diseases.