"When you're in an outbreak situation with a very contagious disease, you really want to make sure you get protection to as many people as possible," said Dr. Jeffrey Avner, the chair of pediatrics at Maimonides Children's Hospital in Borough Park, Brooklyn.
As he explained it, doctors do not typically administer the vaccine in a non-outbreak environment before a child is a year old because the baby still carries a passive immunity from their mother.
That immunity, in the form of antibodies, can attack or, as he puts it, "stick" to the vaccine and prevent a robust response to the measles virus.
However, in an outbreak, all bets are off. Avner said he believes a reduced immunity is still better than being completely unvaccinated.