Transmission of SARS-CoV-2 associated with aircraft travel: a systematic review

Air travel may be associated with the transmission of viruses, given the high number of people traveling in close proximity to each other. We set out to evaluate relevant data on SARS-CoV-2 transmission aboard aircraft, report any important implications for policymaking, and highlight areas where further research is needed.

The evidence we found indicate SARS-CoV-2 transmission aboard aircrafts is low. However, published data do not allow any conclusive assessment of the likelihood and extent of transmission, as evidence from most studies is of low quality. Variations in study designs and methodologies also limit the ability to compare findings across studies. We consider standardized guidelines are needed for future studies of SARS-CoV-2 transmission on aircraft.

What did we do?

We searched for studies on SARS-CoV-2 transmission aboard aircraft published between 1 February 2020 and 27 January 2021. We assessed study quality based on five criteria and reported essential findings.

What did we find?

We identified 20 eligible studies. Eighteen assessed in-flight transmission of SARS-CoV-2, representing 130 individual flights. Two studies investigated the presence of the virus in wastewater from aircraft. In most studies, the quality of evidence was low.

Wastewater studies reported samples positive for SARS-CoV-2 by polymerase chain reaction (PCR). However, cycle threshold (Ct) values were high, ranging from 36 to 40. The Ct value refers to the number of times a sample needed to be amplified before the virus could be detected. A high Ct indicates a low concentration of viral genetic material, which is typically associated with a lower risk of infectivity.

The proportion of traced contacts ranged from 0.68% to 100%. Overall, studies successfully traced 2,800 of 19,729 passengers, 140 of the 180 crew members, and eight out of eight medical staff.

In total, 273 index cases and 64 secondary cases were reported. Among studies following up more than 80% of passengers and crew, secondary attack rates ranged from 0% to 8.2%.

The studies also reported on the possibility of SARS-CoV-2 transmission from asymptomatic, pre-symptomatic, and symptomatic individuals.

Four studies performed genome sequencing and phylogenetic analysis reporting higher-quality reliable evidence. They indicated the aircraft setting might be associated with SARS-CoV-2 transmission. Furthermore, viral cultures of index cases were performed in two studies, generating ten positive results.

About author

Cecilia has completed our short course, Complex Reviews, as part of the postgraduate programme in Evidence-Based Health Care.

References

Transmission of SARS-CoV-2 associated with aircraft travel: a systematic review (Version 1)

EC Rosca, C Heneghan, EA Spencer, J Brassey, A Plüddemann, IJ Onakpoya, D Evans, JM Conly, T Jefferson medRxiv 2021.06.03.21258274; doi: https://doi.org/10.1101/2021.06.03.21258274

Elena C Rosca, MD, PhD, Carl Heneghan, DPhil (Oxon), Elizabeth A Spencer, PhD, Jon Brassey, BSc, Annette Plüddemann, PhD, Igho J Onakpoya, MD, DPhil, David H Evans, PhD, John M Conly, MD, PhD, Tom Jefferson, MD, Transmission of SARS-CoV-2 associated with aircraft travel: a systematic review, Journal of Travel Medicine, Volume 28, Issue 7, October 2021, taab133, https://doi.org/10.1093/jtm/taab133