2019 has seen the resurfacing of measles, with an estimated 465 cases of the disease being reported and confirmed in the United States so far this year.

According to WebMD, measles is a contagious respiratory disease that is spread by a virus. It is so contagious that someone who is not immune to measles may be at risk of catching it if exposed to someone with the disease.

Why exactly has measles resurfaced? In 2000, it was declared eliminated in the United States. According to the director of the Vaccine Education Center at Children’s Hospital of Philadelphia, Paul Offit, MD, “A critical number of parents have chosen not to vaccinate their children.” This decision made by parents in recent years has brought measles back because children are more at risk to catch the disease.

The states that have reported cases this year include Arizona, California, Colorado, Connecticut, Florida, Georgia, Indiana, Kentucky, Massachusetts, Michigan, Missouri, Nevada, New Hampshire, New Jersey, New York, Ohio, Oregon, Texas, and Washington.

New York City, in particular, declared a public health emergency due to an outbreak in the Orthodox Jewish community, which holds resistance to some vaccinations. Mayor Bill de Blasio stated the city will require unvaccinated people living in high-risk ZIP codes to get immunized.

Unvaccinated people are not the only ones at risk of getting measles. The disease will also harm those who did receive a vaccination but whose immune system did not accept the vaccine.

With the rate at which cases are being reported this year, this century’s highest outbreak of 667 cases in 2014 may be surpassed as more and more get infected. The most susceptible group to catch the measles disease are infants, as their immune systems are not fully developed. They are not the only target, however; those who are unvaccinated and those who have weak immune systems also have a high risk of catching the disease.

A single person with measles is said to be able to infect anywhere from 16 to 17 people because of how contagious the virus is.  Healthcare specialists urge parents to vaccinate their children and, if they are unable to receive a vaccination, urge them to protect their children.