The combination measles, mumps, rubella, and chickenpox vaccine is convenient for parents and young children - four vaccines in only one shot. But new research is showing that this combination vaccine may increase the risk of fever-related seizures in children. This information is causing many parents to ask a lot of questions: What does this mean for me and my child? Is the vaccine still safe to get? If my child has already had the vaccine, do I need to worry about any risks?

MMRV Vaccine (ProQuad)
Most young children in the United States get a combination vaccine against the measles, mumps, and rubella known as the MMR vaccine. This has been a routine vaccine for young children since the 1970s. These three diseases used to be common, but since this vaccine was developed they have been almost eradicated in the U.S.¹ In 1995, a vaccine was developed for another routine childhood disease, chickenpox (varicella). Since all children need to get all four of these vaccines, Merck (the company that makes both of them) decided to combine them all into one, called the MMRV vaccine (for measles, mumps, rubella, and varicella), or ProQuad. The Food and Drug Administration (FDA) approved this combination vaccine in 2005, and soon afterwards parents started choosing it for their children, thinking that fewer shots would be better.

At the time of FDA approval, there was evidence of a slightly increased risk of fever-related seizures among children who got the vaccine, but the vaccine was approved with a commitment from Merck to do a large post-marketing study to further understand this risk. Now, these studies are showing that children who get this vaccine are twice as likely to have seizures caused by high fevers.

Fevers and Seizures
All small children are at risk for seizures if they have a high fever, with the risk peaking when a child is between 14 and 18 months old.² This risk is increased slightly after receiving either the MMR vaccine or the chickenpox vaccine. Approximately 1 in 1,000 children who get the chickenpox vaccine will have convulsions,³ and about 3 in 10,000 children will have convulsions after getting the MMR vaccine.¹ These types of seizures are not known to produce any long-term problems.

New Information
Both the Centers for Disease Control and Prevention (CDC) and Merck performed follow-up studies after ProQuad was approved, to see if the risk of convulsions was greater with the combination than with the two vaccines separately. At the February 2008 meeting of the CDC Authorization Committee on Immunization Practices (ACIP), new data indicated that this was true.

The new study, performed by Dr. Nicola Klein at the Kaiser Permanente Vaccine Study Center, showed that the seizure rate among children between the ages of one and two years was about twice as high in children who got the combination vaccine than in children who got the two shots separately.⁴ No children died, and no children experienced any adverse consequences from their seizures.⁴ The study monitored children for 7 - 10 days vaccination. Among the 43,000 children vaccinated with ProQuad, there was a seizure rate of 9 in 10,000 children.⁴ Among the 315,000 children vaccinated with the MMR and chickenpox vaccines separately, there was a seizure rate of only 4 in 10,000 children.⁴

Merck and ProQuad
Although the combination vaccine started being sold in 2005, relatively few children have gotten it because it has been in short supply. Merck stopped making the vaccine because of manufacturing difficulties, but it is expected to be widely available again in 2009.⁴ Originally, the CDC recommended vaccinating children with ProQuad instead of the two separate vaccines. However, due to these new data, the CDC is changing its recommendation and saying that the combination vaccine is no better, and is not preferred.

Merck is also reporting early findings in their own research that the combination vaccine results in more seizures. They agree with Dr. Klein that there is a doubling of the risk of seizure in the first 5 to 12 days after vaccination.⁴

Which Vaccine Should My Child Get?
Getting the vaccines separately and getting the combination vaccine both cost about $124. The ProQuad vaccine is still legal and approved by the FDA,² and no children have died or become seriously ill because of their seizures. The FDA has updated the package insert of ProQuad to inform all health care providers and consumers about these increased risks.² The probability of your child having these convulsions is still relatively low; however, the risk is lower for the two vaccines instead of the combination. It is important to remember that it is safer for your child to get these vaccines than for them to get the diseases they protect against.


Footnotes
1 National Network for Immunization Information. Vaccine Information: Measles. Retrieved February 29, 2008 from: http://www.immunizationinfo.org/vaccineInfo/vaccine_detail.cfv?id=8#effectiveness

2 Food and Drug Administration. (2008, February 29). Information Pertaining to Labeling Revision for ProQuad. Retrieved February 29, 2008 from: http://www.fda.gov/cber/label/proquadlbinfo.htm

3 National Network for Immunization Information. Vaccine Information: Varicella (Chickenpox). Retrieved February 29, 2008 from: http://www.immunizationinfo.org/vaccineInfo/vaccine_detail.cfv?id=11

4 Centers for Disease Control and Prevention. (2008, February 27). What Clinicians Need to Know About MMRV Vaccine Safety. Retrieved February 29, 2008 from: http://www.cdc.gov/od/science/iso/vsd/mmrv.htm