Here is the analysis of 2,482 cases of mumps hospitalization in 1958-1969 in 16 hospitals in England. They constitute the majority of mumps cases that required hospitalization in the country. Half of the patients were 15 years old or older. Complications were recorded in 42% of all cases. Three patients died, but two of them had another serious underlying illness and mumps might not have had anything to do with the death, and the third patient was most probably misdiagnosed and did not even have mumps. The only complication, which may have been permanent, was deafness in five patients (four of them were adults).
Meningitis in mumps happens so often that some people believe it should not even be considered as a complication, but rather an integral part of the disease. In any case, there is a consensus that mumps meningitis is not dangerous and rarely has any consequences. It is confirmed by this study.
What is usually most feared is orchitis. There is a general fear of infertility from orchitis, but its probability is overestimated. Even though it is impossible to exclude, a small retrospective study did not detect infertility as a consequence of orchitis.
The authors conclude that there is no need for mass vaccination against mumps. It might make sense to vaccinate post-pubertal teenagers on admission to boarding school or the army. Even then, however, it should be remembered that 90% of the boys have already had mumps by the age of 14, which is why they should be checked for antibodies first, and only those who do not have the antibodies should be vaccinated.
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.
After the mass MMR vaccination campaign in Brazil with the Japanese strain of mumps (Urabe), an outbreak of aseptic meningitis began. The risk of disease increased by 14-30 times.
The fact that Urabe strain is associated with aseptic meningitis was already known, but Brazilian authorities decided to use this strain anyway, as it is cheaper and more effective than the Jeryl Lynn strain (which is used in the US), and because they thought the risk of meningitis was quite low.
In France, vaccination with the same strain did not cause a meningitis outbreak. The authors attribute this phenomenon to the fact that the outbreaks in Brazil were observed mainly in the large cities, where people live close to hospitals. Moreover, a large number of children had been vaccinated in a very short time. These factors made it possible to identify the outbreak.
The authors worry that such side effects could lead to more people refusing vaccination. They say that people’s belief in the benefits of vaccination is no longer strong enough on its own, and that more and more people refuse vaccination, and that it would not hurt to also record side effects of the vaccination.
The following year, learning from their mistakes, the Brazilian authorities bought MMR with another strain of mumps (Leningrad-Zagreb) and vaccinated 845 thousand children with it. Another outbreak of aseptic meningitis started, and this time the risk of disease was 74 times higher. Sure, it was known that this strain also increases the risk of meningitis, but since the vaccination campaign in the Bahamas did not cause a meningitis outbreak, they decided to see how it would turn out in Brazil. Moreover, a mumps outbreak also began. One out of every 300 doses of the vaccine resulted in mumps.
The authors are wondering whether all the vaccination campaign funding should be used on vaccines, or maybe some of it should be allocated to registering side effects. They write that this issue is quite controversial in the medical literature. Supporters of prioritizing the vaccine believe that benefits of vaccination campaigns are indisputable, and that there is no need to spend money on such nonsense. Proponents of side effects monitoring believe that lack of information scares people and leads to distrust of the vaccines.
Leningrad-Zagreb strain was developed in Serbia on the basis of Leningrad-3 strain, which also caused meningitis.
Cochrane's systematic review of MMR efficiency and safety. The vaccine efficacy is 95% against measles and 88% against mumps.
The vaccine increases the risk of aseptic meningitis by a factor of 14-22 (Urabe and Leningrad-Zagreb strains), the risk of febrile convulsions by a factor of 4-5.7, the risk of thrombocytopenic purpura by a factor of 2.4-6.3.
The authors conclude that clinical and post-clinical safety studies of MMR are largely inadequate and that it is not possible to separate the role of the vaccine in preventing disease from the side effects it causes.
They recommend improving the format and reporting of clinical and post-clinical trials, and standardizing the side effects definitions. It is also required to test the longevity of MMR protective effect.
Study of side effects of 4 different MMR vaccines. 38,000 children were vaccinated. With the standard vaccine, aseptic meningitis (with a laboratory-confirmed vaccine strain of mumps in cerebrospinal fluid) was diagnosed in one in every 600 vaccinated children (aseptic meningitis in general was found in one in 400 after the standard MMR). One in every 350 vaccinated people had non-Meningitis related convulsions (40% of them had non-febrile convulsions).
One of the vaccines did not cause aseptic meningitis. It turned out that its manufacturer had done something wrong about the vaccine strains and did not report it.
In other countries, post-MMR aseptic meningitis was a less common finding (1:4000 to 1:282000) for whatever reason.
As a result of this study the Japanese Ministry of Health banned the use of MMR in 1993, and it is not used there till this day. (The study was being conducted from October 1991 to April 1993, and was published in 1996)