SAN FRANCISCO, CA—Individual elevated risk for immune thrombocytopenia purpura (ITP) following either administration of the combination measles-mumps-rubella-varicella (MMRV) vaccine or MMR with a separately administered varicella vaccine is consistent with previous studies in children ages 1–2 years, Nicola P. Klein, MD, PhD, from the Kaiser Permanente Vaccine Study Center, Oakland, CA, reported at IDWeek 2013.
Measles-containing vaccines increase risk of seizure and fever in toddlers 7–10 days following immunization. Dr. Klein and colleagues evaluated the risk of 7 outcomes in addition to seizure and fever following combination MMRV vs. MMR+V vaccines.
From 2000–2012, data for children aged 12–23 months included in the Vaccine Safety Datalink were examined. The pre-specified post-vaccination risk intervals for acute disseminated encephalomyelitis (Days 3–21, 1–42); anaphylaxis (Day 0); arthritis/arthralgia (Days 1–42); ataxia (Days 14–28, 1–42); ITP I (defined as two platelet counts of ≤50,000/µL within 7 days of each other) and ITP II (defined as two platelet counts of ≤150,000/µL within 7 days of each other, both Days 14–28 [focal risk interval] and 1–42 [broader risk interval); encephalitis/meningitis/encephalopathy (Days 3–21, 1–42); and Kawasaki disease (Days 1–28, 1–56) were evaluated. Outcomes during the risk intervals post-MMRV with those post-MMR+V were compared, as well as outcomes during each risk interval with those during a later control interval using case-centered logistic regression.
A total of 123,200 MMRV doses and 584,987 MMR+V doses were analyzed. Results showed that the difference in risk between the vaccines was not statistically significant during any pre-specified risk interval for any outcome.
In comparing the risk interval with the control interval (case-centered analyses), the investigators found an increased risk of ITP I following MMRV (odds ratio [OR] 11.28, 95% CI 1.87–68.2) and MMR+V (OR 10.04, 95% CI 4.49–22.45), increased risk of ITP II following MMR+V (OR 4.26, 95% CI 2.33–77.7 for days 14-28 and OR 2.81, 95% CI 1.75–4.52 for days 1–42), decreased risk of ataxia after both MMRV (OR 0.7, 95% CI 0.51–0.95) and MMR+V (OR 0.81, 95% CI 0.7–0.93), and increased risk of anaphylaxis after MMRV (OR 15.34, 95% CI 2.16–108.86).
Overall, there were no statistically significant differences in risk for all outcomes when comparing MMRV with MMR+V. “The increased risk for anaphylaxis after MMRV, and the reduced risk for ataxia after both MMRV and MMR+V require more investigation,” reported Dr. Klein. She further remarked that continuous monitoring for anaphylaxis and other outcomes is warranted.