Investigation of COVID-19 Transmission during the First Community Outbreak in a Remote Island Population, Falkland Islands, April to June 2022

Respiratory Diseases

Background: After 2 years of zero Covid-19 transmission, the Falkland Islands (FI) reported their first community Covid-19 case in April 2022. Because of high vaccine coverage (88% of entire population), no specific control measures were instigated, and cases spread rapidly. We undertook a retrospective cohort study to determine the extent of transmission and the effectiveness of Covid-19 vaccine in an infection naive population.

Methods: We extracted data on age, sex and vulnerability for the FI registered population from a patient information system and linked to Covid-19 case line-list and vaccination datasets. Cases were individuals with positive SARS-CoV-2 PCRs or lateral flow tests (LFDs), from 26 April to 30 June 2022. Univariable analyses compared case risk factors to non-cases. Relative vaccine effectiveness was calculated using Poisson regression with robust error variance, comparing against individuals without vaccination in the 20 weeks prior to the outbreak. Models were adjusted for age, sex, extreme vulnerability, and previous infection.

Results: Of the 3,343 registered population, 44% (n=1,467) were cases, with no Covid-19 hospitalisations or deaths. In univariable analysis, being female (RR 1.12, p=0.004) and under 18 years (RR 1.70, p<0.001) were associated with increased Covid-19 risk. Relative vaccine effectiveness was 39.0% (95% CI, 1.03 to 62.5) and 33.0% (95% CI, 8.3 to 51.0) 2 to 9 weeks after receiving 2nd and 1st boosters respectively.

Conclusions: We showed widespread transmission, disproportionately affecting children and women, indicative of transmission in educational and household settings. Despite limited natural immunity, our findings suggested that vaccination was effective in protecting against severe disease and booster doses provided additional short-term protection against infection. We would recommend optimizing coverage with boosters of vaccines in remote island populations such as FI. Follow-up would be needed to assess duration of protection after booster vaccination.

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