Data Analysis Finds Threshold for Lifting/Reinstating Masking to Combat Respiratory Illness


Research showed that 600 hospital beds filled with patients with severe illness would be enough to reimplement (mask mandates to stop the spread of infection.

Nonpharmaceutical interventions (NPIs) can control the spread of COVID-19 and other infectious diseases such as respiratory syncytial virus (RSV). Mandate mask-wearing, social distancing, school and business closures, and travel restrictions are favorable forms of NPIs.

Researchers recently identified a threshold control method (TCM) to predict the best time to lift NPIs, which they published in the journal Chaos. The findings come from a large collaboration between Guangdong Second Provincial General Hospital, City University of Hong Kong, Central South University, University of North Carolina Project-China, Chinese Academy of Sciences, and University of Chinese Academy of Sciences.

Experts had observed that countries who lifted NPIs experienced large resurgences in respiratory diseases such as COVID-19 and RSV. The post NPI surges are inevitable, noted the study authors, potentially overwhelming hospital systems.

"We observed resurgences of all 5 respiratory infectious diseases at staggered peak times," said study author Qingpeng Zhang, BEng, MS, PhD, associate professor at the School of Data Science at City University of Hong Kong, in a recent press release. He added that the investigators "identified 4 critical thresholds for reemploying NPIs that will ensure a sufficient supply of hospital beds."

The investigators conducted a model to monitor infectious diseases and the point at which the hospital system would become overwhelmed. The team looked at data of respiratory illnesses, including COVID-19, RSV, rhinovirus/enterovirus, adenovirus, influenza A and B, and parainfluenza, in Hong Kong between 2014 and 2021.

The control period was 130 weeks, or approximately 2.5 years, which strategically matches the duration of time that Hong Kong implemented NPI measures during COVID-19. According to investigators, the model’s simulations confirmed that NPI measures were effective at stopping the spread of respiratory illness among people in Hong Kong.

The results of their model suggest that reintroducing NPI measures at the point at which there are 600 severe cases of respiratory illness could ensure that Hong Kong hospitals do not become overwhelmed with severely ill patients.

NPIs were used to control the spread of COVID-19. While they protect against infectious respiratory illness, NPIs also increase the number of people susceptible to diseases. RSV and respiratory immunity cannot come from a vaccine, unlike influenza, so building immunity against respiratory disease must come via infection.

"Without the TCM approach, there will be 2 waves of respiratory infectious disease outbreaks exceeding the capacity of the hospital system in Hong Kong in 2023 and 2024," Zhang said in the press release. "By implementing strict, or even mild, TCM measures before 600 hospital beds are filled, the rebound of respiratory infectious diseases other than COVID-19 can be fully suppressed to a level that is safe for hospitals."

Most studies assessing post-COVID-19 resurgences of respiratory illness focus on RSV and flu. However, the study authors note that governments should prepare for several epidemics in the coming years.


American Institute of Physics. Preparing for coming RSV, influenza epidemics. January 17, 2023. Accessed January 20, 2023.

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