Afriend called recently asking about measles. She’s the mother of four very young kids and wanted to know if she should be worried. She’d heard about the large measles outbreak in northwest Texas. Since January, more than 159 people are known to have been infected, and the outbreak has resulted in two deaths and dozens of hospitalizations. Now, this measles outbreak has spread into nine other states, and there’s an alert to travelers passing through the Los Angeles Airport.

Contrary to statements by Health Secretary Robert F. Kennedy Jr., outbreaks of this deadly disease are highly unusual. The U.S. declared measles eliminated more than 20 years ago, thanks to an exceptionally safe and effective vaccine. But efforts to undermine confidence in that vaccine have contributed to these recent outbreaks. There are things we can do, individually and collectively, to protect our most vulnerable and hopefully eliminate measles in this country again.

My friend understands the settled evidence behind the safety and efficacy of vaccines. She’s following the vaccine schedule her pediatrician recommended. Measles vaccines are among the most protective shots we have, so when she gets her kids vaccinated, they are protected. But the large outbreaks we are starting to see are still creating risks, including among our very youngest kids, our immunocompromised kids, and even among vulnerable adults.

Measles vaccines are highly effective: 93% after the first dose, 99% after the second dose. The problem is the timing. The first dose is not recommended until a child is 12 to 15 months old, and the second dose usually between the ages of 4 and 6. Infants have some passive immunity from their mom’s antibodies for the first 6 months, but not enough to be fully protective, which is why the U.S. Centers for Disease Control and Prevention strongly recommends that parents of children too young to be vaccinated avoid travel to areas with measles outbreaks.

Read More: What to Know About the Measles Vaccine

All children under the age of 1, before they get their first measles vaccine, are at risk if they come near someone with measles. Given that measles is one of the most contagious diseases on Earth, outbreaks mean we are likely to see more infections among children in this age range, including kids whose parents fully intend to vaccinate. And while the first dose is highly protective, the best protection comes after the second dose, which is usually given when a child is ready to start school. Between those two doses, children may still be at some risk, especially if they come into repeated contact with measles from others refusing or unable to be vaccinated.