Phase 3 study Objectives:

Primary objective: To reduce senior citizens' risk of acute infection during the COVID-19 pandemic.

Secondary objectives: To reduce senior citizens' risk of SARS-CoV-2 infection during the COVID-19 pandemic. To reduce senior citizens' risk of self-reported respiratory illness during the COVID-19 pandemic.

Study design: A placebo-controlled randomized trial. Study population: 1900 seniors 65 years of age or above. Intervention: Participants will be randomized 1:1 to intradermal administration of a standard dose of BCG vaccine or placebo (saline).

Outcomes: Primary outcome: "Acute infection" identified either by a doctor, antibiotics use, hospitalization, or death due to infection.

Secondary outcomes: Verified SARS-CoV-2 infection and self-reported respiratory illness.

With an expected incidence of "acute infection" of 20%, the trial can show a 25% risk reduction in the intervention group versus the placebo group by including a total of 1900 individuals, 950 individuals in each group.

Risk for participants and impact: Based on previous experience and randomized controlled trials in adult and elderly individuals, the risks of BCG vaccination are considered low. If BCG can reduce the risk of acute infection in seniors by 25% it has tremendous public health importance, both during the COVID-19 pandemic and overall.