A measles and rubella vaccine was given to a healthy 31-years-old male. 10 days later he was hospitalized with a viral encephalitis diagnosis, and another 3 days later, he died. RA27/3 rubella vaccine strain was detected both on brain tissue and in cerebrospinal fluid.
Two more similar cases are described here.
In 2013, 15 mumps outbreaks were registered in France. 72% of the cases had been vaccinated twice. The effectiveness of the vaccine was 49% for one dose and 55% for two doses.
Among those who had been vaccinated once, the risk of getting mumps increased by 7% for every year that had passed since the vaccination.
Among those who had been vaccinated twice, the risk of getting mumps increased by 10% for every year that had passed after the second dose.
Orchitis was observed in five men. One of them was unvaccinated, two had been vaccinated with one dose, and another two had been vaccinated twice.
Mumps is a mild disease, which passes on its own, but sometimes it can cause severe complications, such as orchitis, meningitis, pancreatitis or encephalitis, especially in adults. Complications from mumps are observed more often in adults and they are more severe than in children, especially among the unvaccinated.
In other countries, mumps outbreaks are also observed among the vaccinated. The reason for this is the decreasing effectiveness of the vaccine and the lack of natural boosters. Other reasons for the outbreaks could be the initial overestimation of the vaccine effectiveness, insufficient vaccination coverage, or existence of a strain that is not covered by the vaccine.
Outbreaks occurring among the vaccinated and the decreasing effectiveness, both lead to thoughts about a third dose of the vaccine. This kind of an experiment was conducted in the US during the outbreaks in 2009 and 2010. Both times the outbreak subsided a few weeks after the administration of the vaccine. However, the outbreaks always subside at some point, so it was unclear whether it had anything to do with the vaccination. Nonetheless, this and other experiments hint that a third dose of the vaccine might not be a bad idea. Moreover, during the vaccination campaigns in the US, the third dose had few side effects.
They wanted to introduce a third dose of MMR into the national immunization schedule in Netherlands, but changed their mind, since mumps rarely causes complications, and the vaccination coverage among adults is unlikely to be satisfactory.
Mumps outbreaks among the vaccinated, along with this study, led the Ministry of Health of France to recommend a third dose of MMR at times of outbreaks. Even though it is unknown whether the vaccine is effective for those already infected with the virus, it is quite possible that the vaccine will cause a decrease in the contagious period of the vaccinated patients.
The Dutch study determined that two thirds of cases during outbreaks are asymptomatic. The role of asymptomatic patients in the transmission of the disease remains unknown.
Future observations in France, and possibly other countries that would adopt the same recommendation, will help determine whether the third dose of MMR is effective during outbreaks.
A 14 months old boy was given an MMR vaccine, and 4 months later he was diagnosed with a severe combined immunodeficiency. He then successfully underwent a bone marrow transplant, but developed chronic encephalitis, and died at the age of 5. A brain biopsy showed that he had the vaccine strain of the mumps virus in his brain. This was the first case of panencephalitis caused by the mumps virus.
A healthy 12-month-old child was vaccinated with MMR, and in 8.5 months he developed encephalitis (MIBE). A brain biopsy revealed a vaccine strain of measles causing it. The child died after 1.5 months. A few more cases have been reported, but those usually occur to immunocompromised persons rather than to healthy ones.
In general, MIBE is the same panencephalitis (SSPE), a rare measles complication that occurs several years after the disease itself, but MIBE develops within a shorter timeframe and much more aggressive. Another similar case.
In another study out of nine cases of panencephalitis, three patients were vaccinated and two were not. The remaining patients' vaccination status is unknown.
The increase in the proportion of SSPE cases following measles vaccination is reported here. It is also noted that SSPE following vaccination has a shorter incubation period than SSPE following measles infection.
Despite the decrease in cases of measles-induced encephalitis after vaccination, the total number of encephalitis cases has not changed, apparently measles only has been replaced by other viruses.
In Finland the incidence of severe encephalitis cases has only increased since the introduction of MMR.
Here is a report on the measles epidemic in Vietnam in 2008 among 20-year-olds. Out of 15 cases of measles-induced encephalitis, 11 patients were vaccinated, 2 patients were not, and status of the remaining 2 was unknown.
The CDC claims that the mortality rate of measles-induced encephalitis is 15%. However, before the introduction of the vaccine, its fatality was much lower. In 1961 there were 42 reported cases of measles-induced encephalitis with no fatalities.
Case report of measles-induced encephalitis following by disability and blindness in a girl after measles vaccination in 1969.
The risk of measles-induced encephalitis increases with age. Essentially, the vaccine, which actually pushes the disease to a later date, significantly increases the risk of measles-induced encephalitis.
A 2017 British study reported that although the number of cases of measles-induced and mumps-induced encephalitis decreased by 97-98% between 1979 and 2011, the overall incidence of encephalitis increased, mainly among infants.