Colorado has recorded its fifth incidence of measles this year, and notably, the latest case involves an adult who had been vaccinated against the disease.
The individual, residing in Denver, reportedly contracted the virus after traveling to Chihuahua, Mexico, a region currently experiencing a measles outbreak.
Previously identified cases in the state include a baby from Denver and a resident of Pueblo, both of whom also traveled to the affected area in Mexico.
In light of this new case, the Colorado Department of Public Health and Environment (CDPHE) has pinpointed a potential exposure site, advising anyone who visited the Kaiser Permanente urgent care clinic at 8383 W. Alameda Ave. in Lakewood between 10:30 a.m. and 1 p.m. on Saturday, April 19, to monitor for symptoms over the next 21 days.
Health officials recommend that individuals who think they may be infected call their doctor’s office or emergency clinic ahead of time to minimize the risk of exposing others in the waiting room.
Dr. Ned Calonge, the chief medical officer at CDPHE, characterized the latest case as a so-called ‘breakthrough’ infection since it occurred in a vaccinated person.
While such cases are rare, they are not entirely unexpected.
The MMR vaccine, consisting of two doses, is estimated to be 97% effective in preventing measles. A single dose is around 93% effective, indicating that an average of three out of every 100 vaccinated individuals may still contract the virus if exposed.
Dr. Calonge further explained that breakthrough infections generally result in milder illness, which aligns with the current Colorado case where the involved individual is reported to be feeling well.
Additionally, he noted that vaccinated individuals who do contract the infection are also less contagious than unvaccinated individuals.
It’s important to clarify that this breakthrough infection does not indicate a mutation of the virus that allows it to evade immune responses more effectively. Rather, in rare instances, some people may not develop adequate immunity from the MMR vaccine, or their immunity may diminish over time.
The state health officials are optimistic about the health system’s capacity to respond to measles cases effectively. However, it was observed that several earlier cases had delays in reporting suspected infections, prompting reminders to clinics and labs regarding the need for timely reporting.
In the latest incident, there was a nearly week-long wait between the individual’s clinic visit and the public announcement of the confirmed measles case. Dr. Calonge clarified that the clinic promptly informed CDPHE of the case, and the delay in public notification was due to deliberations over the individual’s vaccination status and uncertainty regarding the test results.
“The decision was, based on the vaccination history, that the likelihood was low,” Dr. Calonge concluded.
Regardless, he stressed the importance of isolation for anyone tested for measles until definitive test results are available.
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