CDC Reminder: Varicella, MMR Vaccines Should Be Given at Least 30 Days Apart

ATLANTA (Reuters Health) Nov 29 - The US Centers for Disease Control and Prevention has affirmed its recommendation that physicians should either administer varicella vaccine simultaneously with the measles-mumps-rubella (MMR) vaccine or wait at least 30 days if the vaccines are administered separately.

Writing in the November 30th issue of the agency's Morbidity and Mortality Weekly Report, CDC researchers report that when the two vaccines are given fewer than 30 days apart but not simultaneously, there is a 2.5-fold increased incidence of breakthrough varicella, which they define as a case of varicella that occurs more than 42 days after varicella vaccination.

According to Dr. Aisha Jumaan, of the CDC's National Immunization Program, antibody titers do not get as high as needed for immunity if one vaccine is followed by the other within 30 days, because they are both live vaccines.

"You need that 30-day period for the body to respond well to the second vaccine," she told Reuters Health. Dr. Jumaan said CDC researchers investigated the interaction with varicella vaccine because of previously reported interactions between the MMR vaccine and the smallpox (variola) vaccine. They suspected that a similar reaction might occur because both the varicella vaccine and the smallpox vaccine contain live pox viruses.

The CDC analyzed data taken from the Vaccine Safety Datalink project, which included over 100,000 children between the ages of 12 and 71 months. The researchers also assessed the incidence of breakthrough disease after administration of other types of vaccines including the diphtheria, tetanus, and pertussis vaccine; Haemophilus influenzae type B vaccine; oral poliovirus vaccine; inactivated poliovirus vaccine; and hepatitis B vaccine.

None of the vaccines other than MMR appeared to increase the incidence of breakthrough disease, whether they were given simultaneously or within 30 days of varicella vaccine.

Dr. Jumaan noted that less than 1% of children receiving varicella vaccine received another vaccine within less than 30 days, "so it is a small number. It could be that these cases resulted from a child being vaccinated by more than one provider, without telling each provider."

"Clinicians should already be aware of this recommendation for administering MMR and varicella vaccines," Dr. Jumaan said. She also pointed out that "there's no increased risk for adverse events with administering the vaccines simultaneously, and it reduces the number of visits a parent has to make to the clinic."

MMWR Morb Mortal Wkly Rep 2001;50:1038-1041.