In 2016 and 2017, the number of mumps cases in Massachusetts was 250 and 170, respectively, a large increase from the average of 10 cases annually in the state. Most patients in these outbreaks had been vaccinated, and some researchers speculated that this could have meant that the virus had mutated in a way that made conventional vaccines no longer effective.
But a February 11, 2020 Reuters article described how Pardis Sabeti, professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, and her colleagues analyzed the virus genome and found no evidence that the virus had mutated in such a way.
“What [our findings] seem to suggest is this is waning immunity, and not vaccine escape,” Sabeti said.
Read the Reuters article: How disease sleuths used sequencing to link mumps outbreaks in Massachusetts