Before revision:  We show that, during the outbreak of a disease, segregating people that are against vaccination from the rest of the population decreases the speed of recovery and may increase the number of cases . Then, we include endogenous choices based on the tradeoff between the cost of vaccinating and the risk of getting infected. We show that the results remain valid under endogenous choices, unless people are too flexible in determining their identity towards vaccination .
After revision:  We show that, during the outbreak of a disease, segregating people that are against vaccination from the rest of the population decreases the speed of recovery and may increase the number of cases and make the disease endemic. The dynamics of the shares of the two cultural traits in the population is crucial in determining the sign of the total effect on the cumulative infection: more homophily is beneficial if agents are not too flexible in determining their identity towards vaccination .