Pa. reports measles cases in 4 vaccinated residents. The rare breakthrough cases are less than 1% of the spreading outbreak
Experts say breakthrough measles cases in vaccinated people are possible, but rare.
Four Pennsylvanians who were vaccinated against measles have contracted the highly contagious illness, state officials announced Friday.
Called “breakthrough cases,” such infections in vaccinated people are rare. The Centers for Disease Control and Prevention estimates that about three in 100 people who received the two recommended doses of the measles, mumps, and rubella vaccine will contract the disease if exposed. About 7 in 100 people who received one dose will contract the disease.
But breakthrough cases do sometimes occur if someone’s immune system “did not respond as well” as most patients’ to the vaccine, the CDC says.
Other times, vaccinated people can become sickened by the virus if they’re exposed for a long period to the disease — like living in a house where multiple unvaccinated people have measles. Vaccinated people tend to have a milder illness when this happens, and they’re less likely to spread measles to others.
The four breakthrough cases reported in Pennsylvania occurred in three adults and one child in Centre, Jefferson, Lancaster, and Lycoming Counties.
The state said that all of them were “appropriately vaccinated for their given ages.” None required hospitalization.
Before Friday, the state had identified no cases this year in people who were fully vaccinated. The breakthrough cases reported Friday make up less than 1% of the total cases reported in the state this year.
Pennsylvania is in the midst of the biggest measles outbreak in more than 30 years, with 676 cases reported and 124 people hospitalized as of Friday.
The state recorded 52 new cases in the last two days alone.
“The presence of so few cases among vaccinated individuals in Pennsylvania out of the more than 670 total cases confirms what decades of clinical evidence show: two doses of the MMR vaccine remain the single best protection against measles,” state officials said in a news release.
Editor’s note: This is a developing story and will be updated.
