The federal Centers for Disease Control and Prevention (CDC) has warned that mumps continues to circulate in the US and that pediatricians should remain vigilant, even though spread remains low.
Mumps was nearly eliminated under routine childhood vaccinations, as part of the measles, mumps and rubella vaccine, or MMR. Most doctors have never seen a mumps case, researchers noted.
But epidemiologists said doctors should continue to test for mumps, because recent outbreaks have occurred in vaccinated adolescents and some children.
“The key takeaway from our report is it is important for all clinicians to suspect mumps in all patients with parotitis or other mumps complications, regardless of a patient’s age, vaccination status or lack of travel outside the US,” said Mariel Marlow, a CDC epidemiologist and head of the agency’s mumps program, in a video for the journal Pediatrics.
The prevalence of mumps declined more than 99% since 1967, from more than 150,000 cases per year to about 200 in 2003, after a vaccine for the disease was introduced. In 1977, it became a routine part of childhood immunizations.
The median annual number of recent mumps cases is still less than 1% of the figure for 1967, before a vaccine was introduced.
However, researchers said there have been two distinct peaks, in 2006 and 2016. Between 85% and 93% of infected children in the outbreaks were fully vaccinated against the disease.
That suggests the disease, unlike measles and rubella, is endemic in the US. Some recent research has theorized that vaccine-conferred immunity to mumps may wane by early adulthood.
Mumps spreads in ways similar to coronavirus, through respiratory droplets. In 2020 there were just 142 US cases of mumps, compared with a median of 1,328. However, the disease was still widespread geographically, and delays in routine childhood immunization caused by the pandemic could create the conditions for larger mumps outbreaks in the future, researchers said.
Mumps is typically mild, and is best known for the swelling it causes in the parotid gland, near the jaw. However, it can result in serious complications such as brain swelling or hearing loss, complications which occur in less than 1% of cases in the post-vaccine era.