Does TB Vaccination Reduce COVID-19 Infection?: No Evidence from a Regression Discontinuity Analysis

Masao Fukui; Kohei Kawaguchi; Hiroaki Matsuura

There are three limitations to our analysis. First, our analysis focused on the effect on COVID-19 infection due to the data availability. BCG immunization can still prevent from developing symptoms or reduce death once infected by COVID-19. However, given that those with COVID-19 symptoms and their close contacts are more likely to be tested and confirmed, we still capture some effects of BCG immunization on developing symptoms. Second, there is possibility that population (in addition to individual) immunity affects our COVID-19 outcomes. However, we removed out potential population immunity effects of the BCG vaccination by controlling for country-specific unobserved fixed effects. We agree that population immunity effects are another parameter of policy interest. However, we leave this to the future research. Another potential criticism is that people acquired immunity from the actual infection of TB, rather than the BCG immunization. If the effects of the BCG immunization and TB on the COVID-19 infection are the same and the TB infection rate was almost 100% around the 5 change in the vaccination policy, there is a possibility that we failed to pick up any additional effects of the BCG immunization. However, this is implausible. Marks et al. (2018) document that in Vietnam, only around 30-40% of age 30s and 40-50% of older population are infected by TB in 2016. In Thailand, the infection rate of children under 14 years old in 1977, when the vaccination started, was 15.2% (Sriyabhaya et al., 1993) . Since Thailand and Vietnam are among the highest TB burden countries in the sample we study, 4 we view these numbers as upper-bounds. There is also possibility that actual immunization rate did not reflect policy change, but this is also implausible given that BCG vaccination coverage rapidly increased from around 0 to 100% when a universal vaccination policy was introduced, as in Vietnam. Hence, if any BCG-specific effect exists, it should appear at the age of policy change.