Worldwide air journey—particularly packed flights—fueled flu, COVID-19 unfold throughout pandemic, researchers say

A brand new study in The Journal of Infectious Diseases hyperlinks increased intercontinental airline passenger flight volumes to each influenza exercise and COVID-19 case and dying charges, suggesting that short-term journey restrictions and in-flight interventions may gradual illness transmission when coupled with public well being measures. 

Flights from Asia performed a bigger position in illness unfold, the research discovered.

University of Hong Kong researchers analyzed month-to-month international passenger numbers and surveillance knowledge on flu and COVID-19 in 78 nations and US states from January 2019 to July 2024. Then they used a modeling framework to evaluate the connection between flight volumes and illness exercise whereas adjusting for variations in country-level public well being efforts.

“Air travel plays a crucial role in infectious disease spread, creating unprecedented pathways for pathogens to cross global boundaries within hours,” the authors wrote. “The confined environment of aircraft cabins creates ideal conditions for respiratory disease transmission.”

Domestic flight volumes performed lesser position

Greater flight volumes had been considerably tied to increased flu exercise and COVID-19 case and dying charges, with the strongest affiliation with flights from Asia. The results had been constantly stronger for COVID-19 than for flu and had been extra pronounced in nations with more-relaxed disease-mitigation measures.

Asia serves as a important epicentre for respiratory virus emergence and evolution, with East, South, and Southeast Asia functioning as essential reservoirs for novel influenza strains and viral range.

Higher flight volumes from Asia had been linked to 21% increased charges of flu transmission (incidence charge ratio [IRR], 1.21), and North American and European flight volumes additionally appeared to facilitate pathogen unfold. Greater flight volumes from Asia (IRR, 1.72), Europe (IRR, 1.45), and North America (IRR, 1.21) had been additionally all considerably tied to elevated COVID-19 case charges. 

Relative to international flights, home flights had been much less strongly and constantly related to illness transmission, which the authors mentioned doubtless mirrored the supply of different within-country transportation choices.

Higher worldwide passenger numbers—particularly on Asian flights—straight elevated infectious illness importation frequency, driving group unfold in vacation spot nations.

“Asia serves as a critical epicentre for respiratory virus emergence and evolution, with East, South, and Southeast Asia functioning as important reservoirs for novel influenza strains and viral diversity,” the researchers wrote. “The region’s dense population centres, proximity of humans to livestock, and ecological conditions create ideal environments for viral emergence and reassortment.”

Balancing public well being, socioeconomic issues 

The constantly stronger hyperlink between flight volumes and COVID-19 could also be as a result of virus’s longer incubation interval (2 to 14 days vs 1 to 4 days for flu) and vital proportion of asymptomatic individuals who could journey with out realizing that they’re infectious.

Decision-makers ought to implement complete methods tailor-made to particular pathogens and variants, balancing public well being safety with financial and social issues primarily based on pathogen traits, outbreak section, and native context.

The authors mentioned that time-limited worldwide flight restrictions could gradual pathogen transmission throughout outbreaks, particularly in nations with less-stringent home controls. But for endemic or seasonal outbreaks, more-sustainable approaches resembling the usage of in-flight preventive measures (eg, enhanced air flow, routine disinfection, obligatory mask-wearing) could also be extra broadly acceptable to policy-makers and the general public. 

“Future response strategies should incorporate these differential impacts when implementing travel-related containment measures, balancing public health protection with socioeconomic considerations,” they concluded. “Decision-makers should implement comprehensive strategies tailored to specific pathogens and variants, balancing public health protection with economic and social considerations based on pathogen characteristics, outbreak phase, and local context.”