Top 5 Takeaways

1. High Vaccination Rate: Over 98% of the ship’s approximately 350 personnel were fully vaccinated against COVID-19.
2. Outbreak Identification: The outbreak was identified on July 27, 2021, when a symptomatic crew member tested positive for SARS-CoV-2.
3. Attack Rate: The attack rate of COVID-19 on the ship was 6.3%, significantly lower than earlier outbreaks on U.S. Navy ships before vaccination.
4. Delta Variant: Most cases were identified as the Delta variant AY.9 lineage, with 16 of 17 specimens being identical.
5. Prevention Measures: Immediate reimplementation of masking, physical distancing, and isolation measures helped limit the spread of the virus.

Original Article Author and Citation

Corresponding Author

Tammy Servies, tammy.e.servies.mil@mail.mil

Suggested Citation

Servies TE, Larsen EC, Lindsay RC, et al. Notes from the Field: Outbreak of COVID-19 Among a Highly Vaccinated Population Aboard a U.S. Navy Ship After a Port Visit — Reykjavik, Iceland, July 2021. MMWR Morb Mortal Wkly Rep 2022;71:279–281. DOI: http://dx.doi.org/10.15585/mmwr.mm7107a5

Summary

On July 27, 2021, a fully vaccinated crew member on a U.S. Navy ship tested positive for SARS-CoV-2 after showing symptoms for four days. The ship, with over 98% of its 350 personnel vaccinated, had recently visited ports in Norway and Reykjavik, Iceland. Despite the high transmissibility of the Delta variant, the outbreak resulted in a 6.3% attack rate, significantly lower than earlier outbreaks on Navy ships before vaccination. Immediate prevention measures, including masking and physical distancing, were reintroduced to control the spread.

Methods

After the initial positive case, all personnel were instructed to report symptoms, leading to the identification of 11 additional cases on the same day. Prevention measures such as mask use, physical distancing, increased cleaning, and isolation of patients were implemented. Close contacts and unvaccinated individuals were tested and quarantined. Nasal swabs from positive cases were sent for RT-PCR testing, confirming the Delta variant.

Discussion

The outbreak on the U.S. Navy ship demonstrated that high vaccination rates combined with immediate prevention measures can significantly reduce the spread of COVID-19, even with the highly transmissible Delta variant. The attack rate was much lower compared to earlier shipboard outbreaks before vaccines were available. The findings highlight the importance of vaccination and multicomponent prevention strategies in controlling SARS-CoV-2 transmission.

Conclusion

This outbreak underscores the effectiveness of high vaccination coverage and prompt implementation of prevention measures in limiting COVID-19 spread in a confined environment. Despite infections among vaccinated personnel, symptoms were mild, and no severe cases or deaths occurred. These findings support the critical role of vaccination and comprehensive prevention strategies in managing COVID-19 outbreaks.

This has been your booster shot of MMWR Info! Please check back for more MMWR, Public Health, and Programming Tutorial content daily.