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Learning from Covid-19: How effective are barriers, filtration and disinfecting strategies against the flu?

The National Academy of Medicine (NAM) recently released four reports on applying lessons learned from Covid-19 to prepare for and respond to the next flu pandemic. The reports provide recommendations on leveraging Covid-19 vaccine technology for influenza vaccine research and development, bolstering the influenza vaccine supply chain, improving global coordination, and effectively using non-vaccine public health measures, such as face masks, physical distancing and school closures, as well as indoor environment controls such as barriers, ventilation and filtration, and various disinfection technologies.

A flu pandemic comparable to that of 1918, which caused an estimated 50 million deaths worldwide, could potentially have worse consequences than the ongoing Covid-19 pandemic, the reports say. Influenza remains the circulating pathogen most likely to cause a pandemic, and the risk for pandemic influenza may be higher during the Covid-19 era due to changes in global and regional conditions affecting humans, animals, and their contact patterns. Each year, there are 3 million to 5 million cases of influenza globally, and up to 650,000 deaths.

Influenza remains the circulating pathogen most likely to cause a pandemic, according to the report. Image courtesy National Academies

The reports also emphasize the need for a preparedness framework. The global cost of responding to a pandemic in a one-year period is estimated to be $570 billion, while investments in pandemic preparedness would cost just $4.5 billion annually, according to the World Bank International Working Group on Financing Preparedness.

Indoor environment controls

Occupational and environmental health and safety (OEHS) professionals group AIHA summarized the section of the report that deals with controls in indoor environments, which covers the efficacy and strength of evidence for the use of barriers, ventilation and filtration, ultraviolet inactivation, ionization, and surface cleaning.

AIHA pointed out the research findings that ventilation and air filtration are “moderately effective at reducing transmission of respiratory viruses;” barriers are “among the least effective interventions for reducing transmission;” surface cleaning has ” low efficacy for limiting transmission for SARS-CoV-2″ but “may be more effective for other pathogens such as influenza virus;” ionization also has “low efficacy;” and ultraviolet germicidal irradiation (UVGI) is “moderately effective at inactivating SARS-CoV-2 on surfaces” when used within certain parameters.

The AIHA summary noted that “other sections of the report address the effectiveness of actions that individuals and governments can take to limit transmission of respiratory viruses,” noting particularly that “strong evidence exists that ‘properly designed, well-fitting face masks with multiple layers of material and strong filtration capacity’ are highly effective at limiting transmission.”

See the AIHA summary of Public Health Lessons for Non-Vaccine Influenza Interventions for a more detailed analysis of the findings on indoor environment controls.

The four reports carried out by the National Academies of Sciences, Engineering, and Medicine are:

All four are available as free downloads from the National Academies website. The Public Health Lessons report contains the section on indoor environmental controls.

First U.S. flu outbreak since pandemic

Another article from AIHA cites a recent CDC report about the University of Michigan in Ann Arbor, which was the site of the first substantial flu activity in the U.S. since the start of the Covid-19 pandemic. In the period from October 6 through November 15, 745 (24%) of 3,121 people who were tested for respiratory illnesses were positive for influenza A, compared to 137 for SARS-CoV-2, and 84 for respiratory syncytial virus. Among those infected with flu, one patient was hospitalized.

Influenza A(H3N2) Outbreak on a University Campus — Michigan, October–November 2021” is available from the CDC website.