- Kenny Lin, MD, MPH
The lower efficacy of COVID-19 vaccines against the SARS-CoV-2 Omicron variant due to viral mutations and waning immunity of the initial series has unfortunately fueled an anti-vaccination narrative that a less-than-perfectly protective vaccine has little clinical value. A comparison to a well-established childhood vaccine exposes the flaw in this argument. According to a 2020 Cochrane review, the effectiveness of measles, mumps, and rubella (MMR) vaccine in preventing mumps is 72% after one dose and 86% after two doses. After the two-dose MMR vaccine was added to the U.S. childhood immunization schedule, though, the number of reported cases of mumps fell from >150,000 in 1968 to 231 in 2003. In the past two decades, outbreaks have occasionally increased the incidence to several thousand reported cases per year.
A recent study in Pediatrics examined the epidemiology of mumps in U.S. children and adolescents from 2007 to 2019. It found that 87% of children diagnosed with mumps during this period had received at least one dose of MMR vaccine, including most of the 2% of children who required hospitalization. Also, only 2% of cases were associated with international travel. The authors concluded that "clinicians should suspect mumps in patients with parotitis or mumps complications, regardless of age, travel history, and vaccination status."
For family physicians who have never seen a patient with this infection, a 2014 American Family Physician article on salivary gland disorders noted that mumps typically causes bilateral pain and edema of the parotid glands, otalgia, and trismus. Rarely, it can cause meningitis and encephalitis, as illustrated in a recent BMJ case report. Mumps spreads through airborne droplets (salivary, nasal, and urinary secretions) and is highly contagious. The diagnosis should be confirmed with reverse transcriptase-polymerase chain reaction (RT-PCR) or viral culture of a sample obtained with a buccal swab.
In fully vaccinated individuals, giving a third or "booster" dose of MMR vaccine was shown to reduce the risk of mumps during a 2015-16 U.S. college outbreak and 3 separate outbreaks in Queensland, Australia in 2017-18. Based on these studies, in 2018 the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices recommended that MMR-vaccinated individuals who are "part of a group or population at increased risk for acquiring mumps because of an outbreak" should receive a third dose of MMR vaccine "to improve protection against mumps disease and related complications." Sound familiar? Family physicians should continue to recommend that patients receive authorized COVID-19 vaccines and booster doses and not let the perfect be the enemy of the good.