Chickenpox vaccine may wear off

Merck’s chickenpox vaccine Varivax not only loses its effectiveness after a while, but it also has changed the profile of the disease in the population, U.S. researchers reported Wednesday.

The study confirmed what doctors widely knew -- that the vaccine’s protection does not last long. And with fewer natural cases of the disease going around, unvaccinated children or children in whom the first dose of the vaccine fails to work have been catching the highly contagious disease later in life, when the risk of severe complications is greater, they said.

“If you’re unvaccinated and you get it later in life, there’s a 20-times greater risk of dying compared to a child, and a 10 to 15 times greater chance of getting hospitalized,” said Jane Seward of the Centers for Disease Control and Prevention in Atlanta, who worked on the study.

The findings were reported fully for the first time in the March 15 issue of the New England Journal of Medicine.