Study Finds Enforced Masking on Long Flights Prevents SARS-CoV-2 Transmission

In a recent study published in the International Journal of Environmental Research and Public Health, researchers in the United States conducted a systematic review to identify factors influencing the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on flights.

Background The COVID-19 pandemic, driven by the rapid global spread of SARS-CoV-2, was significantly facilitated by air travel. As a result, many countries implemented strict disease mitigation measures, including restricting air travel and closing other modes of long-distance travel. These measures led to substantial losses in airline and tourism revenues, prompting governments to provide financial assistance to the aviation industry.

Although global travel and tourism have nearly returned to pre-pandemic levels, the emergence of new SARS-CoV-2 variants continues to pose a risk of severe COVID-19 outbreaks. The U.S. Centers for Disease Control and Prevention (CDC) have highlighted that virus transmission is more likely in enclosed spaces with minimal distancing, such as aircraft. Therefore, understanding the factors that increase virus transmission on planes is crucial.

About the Study The researchers reviewed published reports on the possible transmission of SARS-CoV-2 inside commercial aircraft. They analyzed data to identify significant factors affecting virus transmission within aircraft cabins.

Transmission of airborne diseases in enclosed spaces like aircraft cabins depends on factors such as mechanical ventilation, flight duration, and the number of individuals in the cabin. Despite the use of high-efficiency particulate air (HEPA) filters, there have been instances of SARS-CoV-2 transmission on planes. However, a clear understanding of the risk factors, including strict masking and flight duration, is still needed.

The review included reports with index cases and flight duration information, excluding those involving non-commercial flights or lacking flight data. Flights were categorized based on masking enforcement—either voluntary or strict protocols for passengers and flight attendants. Mealtimes were assumed to be periods when masks were not worn on long-haul flights.

Only flights with index cases were analyzed to ensure that SARS-CoV-2 transmission occurred from an infected individual on the flight. The study investigated the relationship between flight duration and virus transmission by grouping flights into haul types and analyzing the infection ratio, calculated by dividing the number of aircraft-acquired SARS-CoV-2 cases by the number of index cases.

Results The study found that long-haul flights without enforced masking had a 25.93-fold increase in COVID-19 incidence rates compared to short-haul flights, while medium-haul flights had a 4.66-fold higher incidence rate. However, long-haul flights with enforced masking reported no SARS-CoV-2 transmission, indicating the significant protective effect of masking.

In flights with unenforced masking, each additional hour of flight duration increased the transmission incidence rate by 1.53-fold. Shorter flights were found to be safer due to reduced exposure to aerosols and the absence of meals, which lower the probability of aerosol particle expulsion and contact.

Long-haul flights with enforced masking reported almost no SARS-CoV-2 transmission despite serving meals, likely because passengers ate quickly and flight attendants ensured proper mask usage.

Conclusions The study concluded that flight duration is a factor in SARS-CoV-2 transmission on flights with non-enforced masking. In contrast, long-haul flights with enforced masking reported no transmission, despite meal service. Each additional hour of flight duration was associated with a 1.53-fold higher probability of viral transmission in flights without enforced masking. These findings underscore the protective effect of face masks against SARS-CoV-2.