Abstract
Militaries worldwide have been affected by COVID-19 pandemic. However, the impact and epidemiological characteristics of transmission during the early phase of the pandemic is not well-studied. This study aims to systematically estimate the baseline incidence of COVID-19 in the military worldwide and identify the potential risk factors of transmission and clinical characteristics of the cases. English and Chinese literature reporting COVID-19 cases in military worldwide published on four electronic databases (PubMed, Scopus, EMBASE, and CKNI) through 28 May 2021 were systematically screened and synthesized qualitatively. Forty-six studies involving at least 711,408 military personnel in 17 countries were synthesized. Low incidence of cases was observed in the military with pooled COVID-19 incidence of 0.19% (95%CI: 0.00-9.18%). We observed a higher incidence among those (1) with overseas exposure (39.85%; 95%CI: 0.00-95.87%) rather than local exposure (3.03%; 95%CI: 0.00-12.53%), (2) who were on either local/overseas military deployment (26.78%; 95%CI: 0.00-71.51%) as compared to those not deployed (4.37%; 95%CI: 0.00-17.93%), and (3) on overseas military deployment (39.84%; 95%CI: 0.00-95.87%) as compared to local military deployment (3.03%; 95%CI: 2.37-3.74%). The majority of the cases were symptomatic (77.90% (95%CI: 43.91-100.00%)); hospitalization and mortality rates were low at 4.43% (95%CI: 0.00-25.34%) and 0.25% (95%CI: 0.00-0.85%), respectively; and headache, anosmia, ageusia, myalgia, nasal congestion, and cough were the most commonly observed symptoms. Overseas and local deployment were observed to have higher risk of SARS-CoV-2 transmission. Sustainable, active SARS-CoV-2 surveillance strategies are crucial to detect and contain transmission early during military deployments.