Transmission of SARS-CoV-2 arising from international flights arriving in Ireland in December 2020: a descriptive analysis using national surveillance data

Abstract

Objectives There is limited evidence on the risk of in-flight transmission of SARS-CoV-2. This study estimated the extent of in-flight SARS-CoV-2 transmission on international flights arriving into Ireland during December 2020. Study design Cross-sectional analysis. Methods National surveillance data identified all notified cases of COVID-19 who were infectious while travelling on international flights to Ireland during December 2020. Close contacts of cases were tested for SARS-CoV-2 and results were collated to estimate the pooled secondary attack rate across all flights. Laboratory and epidemiological data were obtained from the Health Service Executive Covid Care Tracker, a national database of COVID-19 cases in Ireland. Results 165 infectious cases of COVID-19 were identified on 134 incoming flights; 40.0% were symptomatic on board. There were 2,099 flight close contacts identified, of whom 40.9% had results of a SARS-CoV-2 PCR test within 14 days of arrival. The pooled secondary attack rate for these contacts was 7.0%, and was higher among those on flights of ≥5 hours duration (p=0.008). Over half (59.1%) of close contacts had no SARS-CoV-2 test result recorded; reasons included incorrect or absent contact details (26.5%), and no response when contacted (17.8%). Conclusions In this national study investigating transmission of SARS-CoV-2 from international flights arriving into Ireland, the pooled secondary attack rate was 7.0%. International travel is likely to have contributed to the third wave of SARS-CoV-2 infections in Ireland in early 2021. Application of non-pharmaceutical interventions remains central to mitigating the risk of in-flight transmission.

Risk of transmission of SARS-CoV-2 on international flights, a retrospective cohort study using national surveillance data in England

“…Secondary cases were more likely to be found within two rows of an index case. The ndings are consistent with those reported in other studies (14,(18)(19)(20), and highlight the importance of number of index cases, proximity, and vaccination status. Flight duration is shown in our data to potentially be less signi cant a risk factor than in earlier studies (14,19).…”

“…This may be explained by differences in contact de nition as well as other factors such as duration of contact and air quality measures in ights. This nding supports available literature regarding in-ight secondary attack rates (14,(18)(19)(20) whilst strengthening previous results that may have been underpowered due to small sample size (17).…”

“…Contact tracing can be effective in reducing onward transmission of SARS-CoV-2 acquired in-ight (9), though timeliness and completeness are likely to be imperative to success (10-12). To date, estimates of the risk of covid-19 transmission on international ights are based on small studies with ndings that vary from no evidence of secondary transmission (6, 13), or low risk of transmission (3,(14)(15)(16), to high transmission risk (17). Evidence from systematic reviews suggests seat proximity to index case, number of index cases on ight, and vaccination status are factors associated with transmission risk, but also highlight the heterogeneity of ndings (18-21) and over-reliance upon small samples which are more susceptible to bias and confounding.Challenges to the public health response to the pandemic were encountered including in areas such as cross-border travel policy (5,22).…”

A large outbreak of the Kappa mutation of COVID-19 in Cork, Ireland, April–May 2021

“…Although the B.1.617 lineage of SARS-CoV-2 was first detected in India [1,15], there were no linked cases in this outbreak with a known history of recent international travel, and the extent of community transmission was uncertain. Genomic surveillance is essential for effective recognition and containment of VOCs [17,18] and the benefits of enhanced WGS capacity for outbreak control have been highlighted in previous outbreak reports during the pandemic to date [19,20]. However, in this outbreak, there were delays in receiving WGS results due to limited laboratory sequencing capacity.…”

Travel in the Time of COVID: A Review of International Travel Health in a Global Pandemic

“…All WGS available were A2-RP strain [ 39 ] September 2020 India New Zealand Index cases tested positive in MIQ @3 days after flight, followed by sequential identification of 7 additional cases in MIQ and in the community A chain of transmission without direct person-to-person contact by aerosol within MIQ; transmission in-flight, and within households; WGS analysis helped to identify probable direction of transmission between cases [ 49 ] September–October 2020 UAE New Zealand 7 positive PCRs among 86 passengers on a flight from Dubai, UAE Flight EK448: cases originated from Switzerland (2), Ukraine, Ireland, India, South Africa (2) before layover in Dubai; 5 had negative pre-departure PCR. All 7 SARS-CoV-2 genomes were genetically identical, except for a single mutation in 1 sample [ 50 •] December 2020 International Ireland 165 cases on 134 flights; 40% symptomatic on board National study of SARS-CoV-2 on 2098 inbound international flights and estimated 135,900 passengers in December 2020; secondary attack rate of 7.0%, higher on flights ≥ 5 h [ 51 ] April 2021 India Hong Kong 59 PCR-confirmed cases among 146 passengers; 20% symptomatic Delhi-Hong Kong flight: 5 positive upon arrival. 7 were estimated to be infected prior to travel, 41 infected during transit, 11 infected in quarantine.…”