Influence of military preventive policy for recruit training on COVID-19 seroconversion: the IMPACT-COVID-19 study

Abstract

Introduction Recruitment and training is vital to maintaining the size, deployability and effectiveness of armed forces, but was threatened early in the COVID-19 pandemic. Reports suggested asymptomatic seroconversion driving SARS-CoV-2 transmission in young adults. Potential association between lower vitamin D status and increased infection risk was also highlighted. We aimed to prospectively determine seroconversion and test the hypothesis that this would vary with vitamin D supplementation in representative populations.

Methods Two cohorts were recruited from Yorkshire, Northern England. Infantry recruits received daily oral vitamin D (1000 IU for 4 weeks, followed by 400 IU for the remaining 22 weeks of training) in institutional countermeasures to facilitate ongoing training/co-habitation. Controls were recruited from an un-supplemented University population, subject to social distancing and household restrictions. Venous blood samples (baseline and week 16) were assayed for vitamin D and anti-SARS-CoV-2 spike glycoprotein antibodies, with additional serology (weeks 4, 9, 12) by dried blood spot. The impact of supplementation was analysed on an intention-to-treat basis in volunteers completing testing at all time points and remaining unvaccinated against SARS-CoV-2. Variation in seroconversion with vitamin D change was explored across, and modelled within, each population.

Results In the military (n=333) and University (n=222) cohorts, seroconversion rates were 44.4% vs 25.7% (p=0.003). At week 16, military recruits showed higher vitamin D (60.5±19.5 mmol/L vs 53.5±22.4 mmol/L, p<0.001), despite <50% supplementation adherence. A statistically significant (p=0.005) effect of negative change in vitamin D (%) on seroconversion in recruits (OR of 0.991 and 95% CI of 0.984 to 0.997) was not evidenced in the University cohort.

Conclusion Among unvaccinated populations, SARS-CoV-2 infection of infantry recruits was not reduced by institutional countermeasures, versus civilians subject to national restrictions. Vitamin D supplementation improved serum levels, but the implementation did not have a clinically meaningful impact on seroconversion during military training.

Rights

This content is not covered by the Open Government Licence. Please see source record or item for information on rights and permissions.

Cite as

Downloadable citations

Identifiers

DOI

https://doi.org/10.1136/military-2024-002940

Repository URI

https://www.research.ed.ac.uk/en/publications/6897dd16-0a2b-436d-b3f1-9355b5517915