On Sept. 29, 2020, In a new Letter, published in PNAS, researchers at La Jolla Institute for Immunology (LJI) re-examined the correlation between BCG vaccination and COVID-19 case severity. Their updated analysis, based on data from the Johns Hopkins University Coronavirus Resource Center, compared mortality data in 51 countries.

The LJI team found that tourism trends could account for the mortality differences. They noted that the initial spread of infections in the early stage of the pandemic in Germany was fueled by tourists returning from skiing vacations. The percentage of alpine skiers in different German states correlates well with the reported mortality.