In the U.S. parents can decide to give their child the four-in-one combination MMRV vaccine (measles, mumps, rubella, chickenpox) or two separate vaccines: MMR (measles, mumps, rubella) and a chickenpox vaccine at age 1 to 2.
A booster four-in-one MMRV vaccine, or MMR vaccine and a separate chickenpox vaccine, at age 4 to 6 is also recommended.
In 2008, a related study found that babies who got measles, mumps, rubella, and chickenpox in one shot had twice the risk for fever-related convulsions as those who got two separate shots, with measles-mumps-rubella components in one and chickenpox, or varicella, in the other.
Even though the convulsion risk was quite small with the four-in-one vaccine -- about one additional seizure for every 2,300 MMRV doses given -- the CDC recommends that parents be educated about the increased fever-related seizure risk with the MMRV vaccine at age 1 to 2.
The four-in-one vaccine, called ProQuad, was first licensed by the FDA in 2005, but manufacturing issues led to repeated shortages even before safety questions arose.
In the new study, researchers from the Kaiser Permanente Vaccine Study Center once again examined MMRV-related seizure risk, but this time in older children receiving booster doses of the vaccine.
The study included nearly 87,000 children between the ages of 4 and 6 who got the MMRV vaccine, and about 67,400 who got separate MMR and chickenpox immunizations on the same day.
Since fever-related seizures occur most often in children under the age of 2 and are rare in those over the age of 5, researcher Nicola Klein, MD, PhD, says she was not surprised to find very few seizures and even fewer fever-related seizures in the 4 to 6 age group.
Just one fever-related seizure occurred within a week to 10 days after vaccination in the MMRV group and no fever-related seizures were recorded in the MMR plus varicella group.