Study evaluates effectiveness of indoor vaccine mandates in US cities during COVID-19

Research published in Contemporary Economic Policy reveals that despite widespread adoption of indoor vaccine mandates in major US cities during the COVID-19 pandemic, there is no consistent evidence that these policies significantly increased vaccination rates or reduced COVID-19–related outcomes. The findings contrast with those from other countries, as national mandates abroad boosted vaccine uptake.

For the study, investigators estimated how mandates that restricted access to indoor venues for unvaccinated individuals impacted first-dose uptake, COVID-19 cases, and deaths across 9 US cities through what's called the synthetic difference-in-differences method. The method estimates the effect of a city's indoor vaccine mandate by constructing a "synthetic" control for the city using a weighted average of untreated metropolitan areas that closely matched pre-mandate trends in the outcome of interest.

The scientists found no consistent pattern of statistically significant impacts of the mandates on first-dose vaccine uptake, COVID-19 cases, or deaths across the 9 cities. The results challenge assumptions about the effectiveness of local public health interventions and suggest that local mandates may be less impactful when vaccine coverage is already high, when people can sidestep restrictions by traveling to nearby cities, and when the political environment is highly polarized. The findings could be useful for developing future public health strategies and policies.

We wanted to take a careful, data-driven look at what these policies actually accomplished in the US context. By the time most cities introduced indoor vaccine mandates, vaccination rates were already high, and many unvaccinated individuals were deeply hesitant or resistant, leaving limited room for further gains. Our findings don't suggest that mandates can't work-only that their effectiveness depends on timing, context, and how easily people can sidestep local restrictions."

Elijah Neilson, PhD, corresponding author of Southern Utah University