In 2005, the Food and Drug Administration approved a combo shot for all four—the MMRV vaccine—which provided an alternative to the previous method of giving an MMR vaccine dose (against measles, mumps, and rubella) plus a separate varicella vaccine dose at the same time. (This vaccination strategy is shorthanded as MMR + V.) Thus, the MMRV combo shot meant one fewer shot for children. But, in 2008, post-market data suggested that the MMRV shot might have a slightly higher risk of causing febrile seizures (seizures associated with fevers), which is a very low risk with the MMR + V separate shots.
Febrile seizures are a somewhat common reaction in young children; this type of seizure almost entirely occurs in children under age 5 years, most often striking between 14 and 18 months. The seizures are short, usually less than a minute or two, and they can be caused by essentially anything that can cause a fever—ear infections, vaccines, the flu, etc. For parents, a febrile seizure can be very scary and lead them to bring their child to a doctor or hospital. However, febrile seizures are almost always harmless—the prognosis is “excellent,” as CDC staff experts noted. Nearly all children fully recover with no long-term problems. By age 5, up to 5 percent of all children have had a febrile seizure at some point, for some reason.
Low risks
In post-market studies of the MMRV vaccine, it was very clear that a slightly increased risk of febrile seizures was only linked to the first dose (given at 12 to 15 months, not the second, given at 4 to 6 years). In studies of over 400,000 children, data found that the risk of a febrile seizure after a first-dose MMRV vaccine was 7 to 8.5 seizure cases for every 10,000 vaccinations. That’s compared to 3.2 to 4.2 seizure cases in 10,000 vaccinations with MMR + V. In all, a first-dose MMRV vaccine had about one additional febrile seizure per 2,300 to 2,600 children vaccinated compared with MMR + V.
In 2009, CDC vaccine experts reviewed all the data and updated the vaccine recommendation. They maintained that MMRV and the MMR+V vaccinations are still both safe, effective, and recommended at both vaccination time points. But, they added the nuance that there is a preference (or a default, basically) for using the MMR + V shots for the first dose, unless a parent expressly wanted the MMRV vaccine for that first dose. This skirted the slightly increased risk of febrile seizure in young children, without entirely taking away the option if a parent prioritized fewer jabs and wanted the MMRV. For the second dose, again, both MMRV and MMR + V are options, but the CDC stated a preference for the one-shot MMRV.
