PITTSBURGH (KDKA) — With five people now confirmed to have measles in Allegheny County, is this a cluster or an outbreak?

“The CDC is likely to announce it. we’re not quite sure if they’ll call it an outbreak or a cluster,” says Allegheny County Health Department Director Dr. Karen Hacker.

The official definition of an outbreak is “a greater than expected number of cases.”

It doesn’t imply anything about whether they’re related.

A cluster is a group of cases of a disease or condition at the same time and place.

The first case here, announced Tuesday, is separate from the four others announced Thursday.

Last year, Allegheny County had just one measles case and none in the three years prior.

“This is going to be considered an outbreak,” says Dr. Hacker.

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What about vaccinations? If you were immunized against measles in the 1960s, 70s and 80s, those vaccines were only about 50% effective. But since 1989, the vaccine has been 93% effective.

To be sure, one local primary care physician recommends people ages 30 to 62 have a blood test to check their immunity. But what about skipping that and going straight to a booster?

“If people would rather do that, I think that’s fine and reasonable. The vaccine is safe for almost all populations. It’s not currently recommended by any medical experts,” says Dr. Marc Itskowitz, an internist at the Allegheny Health Network.

When it comes to children, if your baby is not yet old enough to get an MMR vaccine, which protects against measles, they may still be protected. That’s because babies get immunity from their mother during pregnancy, but those antibodies taper off after six months.

Giving a vaccine while the antibodies are still circulating will decrease the effectiveness of the shot, which is why immunization isn’t recommended until later.

If your child is older than 6 months and you’ll be traveling abroad, or if your baby has had a known exposure within 72 hours, your pediatrician may go ahead and vaccinate. But generally, you have to wait until the child is 1 year old.

Dr. Maria Simbra