Children receiving measles-containing vaccines at 12-15 months of age have a lower increased risk of fever and seizures than those who receive them at 16-23 months of age, according to a study.
The CDC recommends a two-dose series of measles-containing vaccines, with the first dose administered at 12-15 months and the second dose at 4-6 years. Most children receive the first dose of a measles-containing vaccine between the ages of 12 and 23 months, with about 85% receiving it by 19 months, according to background information in a news release.
The research, published Oct. 14 on the website of JAMA Pediatrics, found receiving the first dose by 15 months might be safer.
We found that the magnitude of increased risk of fever and seizures following immunization with measles-containing vaccines during the second year of life depends on age, the studys lead author, Ali Rowhani-Rahbar, MD, MPH, PhD, of the Kaiser Permanente Vaccine Study Center in Oakland, Calif., said in the news release.
While measles-containing vaccines administered at 12-15 months of age are associated with a small risk of fever and seizures following immunization, delayed administration at 16-23 months of age results in a greater risk of those adverse events.
Past studies have shown these vaccines administered to children ages 12-23 months are associated with an increased risk of febrile seizures one to two weeks after immunization, according to the news release. This is the period of time during which the vaccine virus replication is at its peak, potentially causing fever. The resulting fever may cause some children to experience a seizure.
Kaiser Permanentes guidelines for measles-containing vaccines are in line with the CDCs recommendations, Matthew F. Daley, MD, a pediatrician and senior investigator at Kaiser Permanente Colorados Institute for Health Research, said in the news release. This studys findings reinforce for patients that these vaccines are safer when children receive them at 12-15 months of age.
While febrile seizures are the most common neurologic adverse events after immunization with measles-containing vaccines, Nicola Klein, MD, PhD, the studys senior author and the co-director of the Vaccine Study Center, noted the risk is small regardless of age. The risk of febrile seizures after any measles-containing vaccine is less than one per 1,000 injections, Klein said in the news release.
Study methodology and results
Using data from the Vaccine Safety Datalink, a collaborative effort of the CDC and nine managed care organizations, Kaiser Permanente researchers evaluated the records of 840,348 children ages 12-23 months who had received a measles-containing vaccine between January 2001 and December 2011.
After immunization with any measles-containing vaccine, the incidence of fever and seizures during days seven through 10 was significantly greater than any other time during the 42-day postimmunization interval in all age groups.
Among the patterns regarding incidence of fever and seizures that were different during the period of observation:
The incidence of fever steadily declined from the period spanning 12-13 months of age to the period spanning 19-23 months of age, while the incidence of seizures was highest among children 16-18 months of age.
The relative risk of fever and seizures during the seven- to 10-day risk interval was significantly greater among children 16-23 months of age than among children 12-15 months of age.
The risk of seizures attributable to the vaccine during the seven- to 10-day risk interval was significantly greater among children 16-23 months of age than among children 12-15 months of age.
Consistent with findings in previous studies, the incidence of fever and seizures during the seven to 10 days after immunization with the measles, mumps, rubella and varicella vaccine was significantly greater than that after immunization with measles, mumps and rubella with or without a separate varicella vaccine.
Study abstract: http://archpedi.jamanetwork.com/article.aspx?articleid=1750204