Influence of Military Preventive Policy for reCruit Training on COVID-19 Seroconversion

The primary aim of the study is to determine the rates of 'silent' seroconversion rates, consistent with asymptomatic transmission of SARS-CoV-2, in a young healthy adult population with a wide spread of vitamin D concentrations. The study will be conducted over 16 weeks in two populations: Service Personnel undertaking initial military training, who are supplementing with vitamin D (1000 IU/day D3 for 4 weeks, and 400 IU/d D3 as a maintenance dose), and civilian students who are not supplementing. We will recruit adults aged 18-30 years old. Military and civilian participants will be recruited respectively in Catterick and Leeds, UK to start in coincidence with the recommencement of Autumn semester. In accordance with our power calculation and anticipated drop-out rate, 450 volunteers will be recruited in each group. Data collected at baseline and after 5, 9, 12 and 16 weeks will include seroconversion status assessed from a validated Dried Blood Spot (DBS) method in conjunction with novel salivary antibody testing, plus structured questionnaire responses screening for Covid-19 symptoms. Physical and demographic characteristics and serum levels of vitamin D concentrations collected from participants at study entry will facilitate secondary aims in relation to exploring the influence of gender, ethnicity, body mass and body mass index (BMI) on asymptomatic seroconversion, as well as interactions with vitamin D status and supplementation.