Measles was eliminated in the US in 2000. And yet progress against the disease has been unraveling to a startling degree, especially this year.
According to the latest measles numbers from the Centers for Disease Control and Prevention, between January 1 and April 11 there were 555 reported measles cases in 20 states. In the past week alone, the CDC has received reports of 90 new cases, mainly in New York state.
That means there have already been more measles cases in 2019 than any year in the last five years. And given that it’s only April, we’re well on track to set a record for the highest number of cases in the US since the disease was eliminated here two decades ago.
So what’s driving the uptick? The outbreaks here have been mostly concentrated in just four states: New York, New Jersey, Washington, and California. And among those, the vast majority of cases (more than 460) have have occurred in Orthodox Jewish communities in New York City and the suburb of Rockland. There, a minority of community members who are vaccine skeptical have been opting out of the shots on behalf of their children, driving vaccine rates down and creating the space for the highly contagious virus to spread.
“More than 70 of the 90 cases [in the last week] were from New York City and New York State,” said Amanda Cohn, the CDC’s senior adviser for vaccines, “and the majority have happened since April 1. So this is an outbreak that’s accelerating.”
But to really understand what’s going on with measles in the US, you have to take a step back and look at the global picture.
All the major outbreaks here are linked to travelers who brought the virus back to the US from countries with ongoing outbreaks, including Ukraine, the Philippines, and Israel. It’s a reminder of how tightly dependent our health can be to that of people in even far-away countries — particularly when we don’t take advantage of tools that can prevent diseases from spreading, like vaccines.
A worldwide surge in measles
Over the past two years, measles cases have been edging up in several countries around the world, with a 300 percent rise in measles cases globally over the same period in 2018, according to the World Health Organization. Right now, Ukraine, Madagascar, India, Pakistan, Philippines, Yemen, and Brazil are among the countries most affected, according to WHO.
Madagascar’s health officials have recorded more than 69,000 measles cases and 1,200 related deaths in the largest-ever measles outbreak on the island nation. Ukraine has experienced 72,000 cases, and the Philippines 19,000 cases.
The reasons for outbreaks differ in each country — from vaccine refusal to problems with health care access or access to vaccines, to civil unrest and low awareness about the need to vaccinate. But what all these causes have in common: These factors are driving down the rate of vaccine coverage.
And in places that used to see very little measles previously, like the US, vaccine skepticism seems to be a common contributor, said Cohn. “There’s vaccine hesitancy in a world where people don’t see measles anymore. We have to continue to remind people how serious measles is.”
How measles spreads in places with high rates of vaccine coverage
The measles virus is indeed one of the most infectious diseases known to man. A person with measles can cough in a room and leave, and hours later, if you’re unvaccinated, you could catch the virus from the droplets in the air the infected person left behind. No other virus can do that.
The good news is that the measles-mumps-rubella vaccine is incredibly effective at stopping measles from spreading. But nearly everybody in a community needs to be vaccinated to achieve what’s known as “herd immunity.”
In order for any vaccine to be effective, you need to have a certain percentage of people in a population immunized. This prevents diseases from spreading through populations, and it protects even those who aren’t or can’t be vaccinated, like newborns and people with vaccine allergies. For measles, 90 to 95 percent of a population need to get the shot. That’s nearly everybody in a community.
Overall, 91 percent of young children in the US got the MMR vaccine in 2016, according to the CDC’s latest data. That’s about enough for herd immunity. But hidden within the national statistics are geographic clusters within states where lots of people are unvaccinated. And it’s in these communities — from New York to Washington — where the virus has been taking off.
When travelers go unvaccinated to these hotspots and bring the virus back to under-vaccinated communities in the US, it’s not difficult for measles to begin spreading.
For a disease to be considered eliminated, all measles cases need to be linked back to an imported case from another country. CDC’s Cohn said that’s still the case with the measles outbreaks here.
“That being said,” she added, “the outbreak in New York City and New York state is concerning just by the length of time this continued transmission has occurred. If these cases continue for an extended period of time — it’s possible for us to not be able to link all the cases back to the imported case.” At that point, America’s great achievement of eliminating measles will be under threat.