Earlier this week, we published a post on how there was no relationship between the spread of notifiable diseases in the United States and immigrant populations. Prior to the COVID-19 crisis, several commentators were concerned that immigrants – especially illegal immigrants – were spreading serious diseases like measles. This is a follow up post focusing on measles specifically, which is one notifiable disease. A legitimate role of immigration policy is to limit the international spread of contagious diseases like measles. However, it’s also important to note the extent of this problem by showing that immigrants do not threaten a measles outbreak.

Methods

Like our earlier post, here we test correlation between the incidence of measles and state-level immigrant population shares for the 2010–2018 period. We use annual, state-level measles data from the CDC’s National Notifiable Diseases Surveillance System (NNDSS), which reports the number of nationally notifiable infectious diseases and conditions by state and year. A notifiable disease is one where the CDC states that “regular, frequent, and timely information regarding individual cases is considered necessary for the prevention and control of the disease.” In addition to other vaccinations, the U.S. Citizenship and Immigration Services requires a vaccination against measles to legally immigrate to the United States.


Foreign-born population data at the state level comes from the American Community Survey (ACS) provided by IPUMS. From the raw ACS microdata, we are able to use the residual technique refined by Christian Gunadi to specifically identify legal and illegal immigrants.

Results

To test whether states with higher immigrant shares experience higher measles infection rates, we run a two-way fixed effects regression to estimate the correlation between the measles rate per 100,000 people and the share of immigrants in a state. The regressions use state and year fixed effects and the standard errors are clustered at the state level. Table 1 shows the results of the regressions. They are all statistically insignificant except a 1 percent increase in the share of a state’s illegal immigrant population is correlated with 0.06 fewer cases of disease per 100,000 state residents at the 5 percent level. Although significant, that’s a very small magnitude. There is no relationship between the share of a state’s population that is foreign-born and the rate of measles per 100,000 residents. There is also no relationship between the legal immigrant share of a state’s population and the rate of disease per 100,000 residents.

Figure 1 shows the lack of a relationship between the immigrant share of the population and the incidence of measles infections on the state level. Figure 2 shows the relationship between the illegal immigrant share of state populations and the incidence of these reportable diseases. The Y‑axes on both graphs don’t line up exactly because they are the measles values fitted with the state and year fixed effects.