Elizabeth Landau, CNN
There are many myths about vaccinations floating around the Internet, says Dr. Simon Hambidge. One -- that giving vaccinations too close together is unhealthy -- has prompted some parents to request that their children receive vaccines on an alternate schedule, Hambidge told CNN in an e-mail.
Hambidge, an expert in pediatric vaccination with Kaiser Permanente's Institute for Health Research Colorado, is lead author of a new study that examines the association between vaccine timing and seizures.
His team found that in the first year of life, there is no relationship between the recommended vaccine schedule and seizures. But delaying the measles vaccine until after a child is 15 months old may raise his or her seizure risk. The study results were published Monday in the journal Pediatrics.
"A number of people have claimed that a young child's immune system is not robust enough to be given multiple vaccines, and that it is safer to 'spread out' vaccination," Hambidge said. "There is no scientific evidence for this, and there is evidence that it is safe and effective to follow the current recommended schedule."
Parents who don't comply with recommended guidelines for childhood vaccines are in a sizable minority.
A study using the 2009 National Immunization Survey found that 25.8% of parents delayed the vaccines, 8.2% refused to get their children vaccinated, and 5.8% both delayed and refused, Hambidge said. The rest did not delay or refuse. These data come from parents of children aged 24 to 35 months.
Parents' fears are mostly about autism, Hambidge said, even though no scientific link has been proven between the two.
For this study, researchers obtained data on more than 300,000 children born between 2004 and 2008. They looked at a variety of different vaccines and their associated seizure risks.
There are two options for vaccinating children against measles: the measles-mumps-rubella (MMR) vaccine plus a separate varicella vaccine, and the measles-mumps-rubella-varicella (MMRV) vaccine. The Centers for Disease Control and Prevention tells parents that while MMRV results in one fewer vaccine, it is associated with a higher risk of seizures.
U.S. health authorities recommend that children receive their first dose of the MMR or MMRV vaccine at 12 to 15 months of age.
The study suggests that children who receive childhood vaccines in the first year of life do not have an associated risk of seizure. But seizure risk may increase in the second year of life with measles vaccines specifically.
The overall risk of seizures in vaccines that contain measles is "real but very low," Hambidge said -- it's about 1 in 4,000 doses, according to previous research. It appears that the risk of seizures is about 2 in every 4,000 doses for children who receive the first MMR vaccine between 16 and 23 months of age.
"Febrile seizures that occur after MMR vaccine are rare and temporary – these children are not at increased risk of epilepsy," Hambidge said. "The risk of catching measles disease is far more serious, especially as we are seeing increased cases of measles in the U.S."
(A febrile seizure is a convulsion in young children that may be caused by a spike in body temperature, often from an infection.)
Meanwhile, the study found that getting the MMRV vaccine, instead of the MMR and varicella vaccines separately, increases the risk of seizures twofold -- regardless of whether the vaccine was given on time. The association with seizures was strongest for children who received the MMRV vaccine between 16 and 18 months of age.
The results support a 2010 study that found additional febrile seizure risk from using MMRV instead of MMR plus varicella separately. But the absolute risk remains small: For every 2,300 MMRV doses given in the second year of life, there is one additional febrile seizure in the seven to 10 days following vaccination.
"This study supports the currently recommended vaccination schedule from the CDC as the best choice for protecting children from serious disease and minimizing adverse events from vaccination," Hambidge said.
Bottom line: Do what your doctor says and vaccinate against measles on time. Have a conversation about MMRV versus MMR if you have questions or concerns. The CDC recommends receiving the MMR and varicella injections separately.
"Because the U.S. is seeing the largest increase in measles cases in recent memory due to unvaccinated travelers returning from trips abroad, the risk of not vaccinating a child for measles or for delaying vaccination is that the child is left vulnerable to catching measles, which is a very serious disease," Hambidge said.
Related: Measles cases at highest level in nearly 20 years
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