A new study from the California measles outbreak shows that a deadly complication from the virus, a progressive brain inflammation, is far more common than was previously thought.
Speaking at the IDWeek conference, James Cherry, a paediatric infectious disease expert from University of California, Los Angeles and a member of the study, said that during the outbreak in 1988-90, there were 16,000 measles cases and 75 deaths.
There were also 17 cases of this brain infection, called Subacute Sclerosing Panencephalitis (SSPE), with 16 of them fatal so far (and the last is close to death).
Forbes has reported that SSPE is a later complication, caused by the measles virus infecting brain cells. It is slowly progressive over years and easily misdiagnosed early on.
Typically, Dr Cherry says, there are three stages of the disease. The first is subtle, with changes in behaviour or the child not doing as well in school. Then mild seizures develop. Finally, the seizures become continuous and coma develops, leading to death.
What is frightening, according to Forbes, in the new study from the California encephalitis project, which looked at all cases of SSPE between 1998 and 2016, is that the rate was 1 in 1,400 for children under five infected, but jumped to 1 in 600 for infants less than one-year-old.
"That is a very frightening surprise," said Dr Cherry. "The answer is good public health. You need to vaccinate everybody and create herd immunity so that you protect those most vulnerable to measles and those at greatest risk of SSPE."
The report comes as the World Health Organization declared the Americas to be free of measles. Gary Marshall, MD of the University of Louisville School of Medicine, who was not involved in the study, said, "That doesn't mean there is no measles. It means that unvaccinated travellers can still bring cases into the country and -- if they have contact with other unvaccinated people -- can cause an outbreak, although there is no widespread sustained transmission."
So far this year, 54 cases have been reported in the US, according to the CDC. The recent record is held by 2014, a year in which 667 cases were reported, the largest total since 2000.