U.S. measles outbreak keeps breaking….

Science News tracks the new outbreak of a disease we’d formally “eliminated”:

The viral disease has sickened at least 555 people in 20 states, according to numbers released April 15 by the U.S. Centers for Disease Control and Prevention.

That’s more than the 372 cases reported for all of 2018 — and it’s only April.

If the outbreak doesn’t get under control, this year could surpass the 2014 high of 667 cases since measles was eliminated from the United States in 2000. Elimination means that the virus is no longer endemic, or constantly present, though it can still be brought in by overseas travelers.

A single person with measles can infect up to 18 others who haven’t been vaccinated. That makes measles more contagious than smallpox or the flu. The measles virus, which invades a person’s throat and nasal cavity, is spread through coughing and sneezing. It can also linger on surfaces or remain in the air for up to two hours, meaning one can enter a room after an infected person left and still be exposed.

The virus usually has a head start over health officials, because an infected person can begin spreading the virus before being diagnosed, which typically happens once the rash shows up. “There’s this four-day window before you got the rash where you’re infectious,” says Daniel Salmon, who heads the Institute for Vaccine Safety at Johns Hopkins Bloomberg School of Public Health.

A few of the areas that have experienced outbreaks are in states that allow non-medical exemptions for vaccines otherwise required for children to start school. Of 18 states that have such policies, 12 have seen rising numbers of vaccine exemptions since 2009, Hotez and his colleagues reported in PLOS Medicine in 2018. “Measles tends to be a good biomarker of declines in vaccine coverage,” Hotez says.

Measles primarily hits those who aren’t vaccinated, but having pockets of low vaccination can also put those who are vaccinated at risk. Of the 1,416 measles cases reported from 2000 to 2015, more than half, or 804, were in people with no history of measles vaccination, Salmon and colleagues reported in 2016 in JAMA. And 199 cases were in people who had received the vaccine, which provides a very high, but not absolute, level of protection.