The CDC was alerted of the individuals by state health officials in New York, California, Illinois, Texas and Washington. That's a awful milestone, but we know exactly why it's happening - all you have to do is look at the people who are coming down with it.
Those with measles can potentially infect up to 15 others if they are not immune and parents should also check their child has had the appropriate MMR vaccine.
The US is experiencing its worst measles outbreak in decades even though it eradicated the highly infectious disease in 2000, according to the CDC.
One dose of MMR vaccine is approximately 93 percent effective at preventing measles, while two doses are approximately 97 percent effective.
Although the disease outbreak did not originate in Americans - it was either brought to the USA by travelers from or Americans returning from countries like Israel, Ukraine and the Philippines - and spread like wildfire among unvaccinated communities, and beyond. State health officials in CT said one case there was a resident who had visited NY.
However, Dr Esper notes that tests of the MMR vaccine found that it is effective against the strain now sweeping the US.
CDC recorded 41 new cases of measles in the past week, bringing the total for this year's outbreak to 880. Adults should get vaccinated for measles if they did not receive the two doses as children.
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As per a US-based Centres for Disease Control (CDC), as of April 26, 704 cases of measles were reported in the U.S. since the beginning of 2019, representing the largest number of cases reported in the country in a single year since 1994, when 963 cases occurred. After a second dose the level of protection is around 99 per cent.
Measles can kill and it is incredibly easy to catch, especially if you are not vaccinated.
There has also been some spread into the wider population, such as those who may have missed out on the MMR vaccine when they were younger. The County of Santa Cruz Health Services Agency offers vaccinations for infants, children, teenagers, and adults.
Mumps cases almost tripled to 795 compared to the 275 during the same period past year, with no new cases of rubella reported.
There was one known secondary case of measles this year, meaning a passenger became infected while traveling from another infected traveler, Cetron told CNN.
In New Zealand, the MMR vaccine is routinely given to children at 15 months and four years old.
The initial symptoms develop 14 to 21 days after a person is infected.