Which vaccine protects against the disease that causes the largest annual epidemic outbreaks in unvaccinated children?

Measles is notorious for causing explosive outbreaks because it spreads so efficiently among unprotected people. The measles vaccine is therefore one of the most important tools for preventing epidemic spread in children and communities. Two doses are usually recommended for strong, long-term protection. When vaccination rates drop, measles can return quickly even in countries that had previously controlled it.