A study of chickenpox and its victims found that many children who have been vaccinated are still getting it.
Like many doctors, Tony Barozzino has seen children who have been vaccinated against chickenpox who still get the disease.
"And either the vaccine didn't take in the first place, which we know happens with all the vaccines, or the vaccine took but it didn't protect them completely," said Dr. Barozzino.
The vaccines were supposed to be 77 to 100 percent effective against chickenpox. But U.S research found it offered only 44 percent protection after tracking one outbreak in New Hampshire, where 25 children, many of them previously vaccinated, got chickenpox.
"They had some immunity, but it wasn't completely protective," said Dr. Karin Galil, an author of the study. "It stopped them from getting a bad case of chickenpox but it didn't protect them from getting infected with the chicken pox virus."
The study could be a sign that for some children, immune protection may not last and that they may need booster shots.
"We are taking very seriously the possibility that we might not have the right optimal vaccination level yet," said Dr. Galil. "And if there's evidence that we need to change it, that will be a priority."
The good news is, that the vaccinated children had milder forms of the disease. In fact, doctors credit the vaccine with cutting the total number of cases of this disease across North America.
"Since we have been using chicken pox vaccine the number of admissions to hospital for severe disease, the amount of chicken pox in the community and the severity of that chickenpox have decreased significantly," said Dr. Stanley Read.
But some are worried the study may be a setback for efforts to expand chickenpox vaccine use.
"I hope it's not used by the government as ammunition to say we don't know enough about it so we should not pay for it," said Dr. Barrozzino.
"There is lots of evidence to say if anything we need to give more of it."
There will be more studies to see if the outbreak is a sign to double up the dose of the vaccine to ensure fewer children get this childhood disease.