Public health experts have taken a fresh look at the safety records of childhood vaccines and once again pronounced them safe.
A systematic review published Tuesday by the journal Pediatrics notes some evidence of "adverse effects" from 11 vaccines. But the authors of the 13-page report emphasize that such problems are "extremely rare" and that the benefits of routine childhood immunizations far outweigh the risks.
"Vaccines are considered one of the greatest public health achievements of the 20th century for their role in eradicating smallpox and controlling polio, measles, rubella and other infectious diseases in the United States," wrote the study authors, a group of experts from Rand Corp. in Santa Monica, UCLA and Boston Children's Hospital.
However, some parents falsely believe that these vaccines cause autism and other health problems, and they are opting out in increasing numbers. "Parental refusal of vaccines has contributed to outbreaks of vaccine-preventable diseases such as measles and pertussis," the study authors wrote.
At the request of the U.S. Department of Health and Human Services' Agency for Healthcare Research and Quality, the researchers scoured the medical literature for the most scientifically rigorous studies on vaccine safety in kids. In addition to the studies examined in a comprehensive 2011 report from the Institute of Medicine, they identified 67 more studies involving controlled trials. Studies using versions of vaccines that aren't available in the U.S. were not included in the analysis.
Here's what the researchers found about each vaccine:
DTaP: The vaccine against diptheria toxoid, tetanus toxoid and acellular pertussis does not cause type 1 diabetes, according to the available evidence. Likewise, there's no evidence to suggest the DTaP vaccine causes any other medical conditions.
Hib: The Haemophilus influenzae type b vaccine can cause redness and swelling but not high fevers, diarrhea, fungal infections, gastroesophageal reflux disease, convulsions or other conditions serious enough to require hospitalization.
Hepatitis A: One of the studies reviewed demonstrated a "moderate association" between this vaccine and purpura, a short-term condition in which leaky blood vessels cause purple spots to appear on the skin. The link was found only in children between the ages of 7 and 17.
Hepatitis B: A 2010 study reported a heightened risk of autism for boys who got this vaccine in their first month of life, but it had methodological flaws that left the authors of the new report unconvinced. They also said that the evidence suggests there is no link between this vaccine and new or relapsing cases of multiple sclerosis. However, children who are sensitive to yeast did have an increased risk of anaphylaxis.
Inactivated polio virus: Although one study found that children who got this vaccine as newborns had a heightened risk of food allergies, the authors of the new report found the evidence too weak to be conclusive.
Influenza: Most studies find no link between flu vaccines and any adverse events, though a few did reveal that kids who got a flu shot (either the live attenuated vaccine that is given through the nose and the inactivated vaccine that's injected into muscle) were more likely than kids who didn't to develop short-term gastrointestinal problems like diarrhea and vomiting. In addition, young children who got the inactivated vaccine had a small increased risk of febrile seizures, especially when they got their flu shots along with the pneumococcal vaccine.
MMR: The vaccine against measles, mumps and rubella does not cause autism, the report authors wrote. However, some versions the vaccine have been linked to an increased risk of febrile seizures, short-term joint pain and purpura.
Meningococcal: The vaccine against meningococcal disease can cause anaphylaxis in children who are allergic to its ingredients, the research team found. However, there is no link between the vaccine and fevers, malaise, hives, muscle pain, headache, changes in eating habits, severe irritability, persistent crying or severe sleepiness.
PCV13: The vaccine against 13 pneumococcal strains does seem to increase the risk of febrile seizures, especially when given in conjunction with a flu shot.
Rotavirus: The primary risks associated with the Rotarix or RotaTeq vaccines were cough, runny nose and irritability. The report authors found moderately strong evidence that the vaccine is linked to intussusception, "a serious disorder in which part of the intestine slides into an adjacent part of the intestine" like a telescope, according to the Mayo Clinic. However, these adverse events are "extremely rare," according to the Pediatrics report.
Varicella: The Institute of Medicine report said this vaccine can cause children to get viruses that cause chickenpox or shingles; those infections can progress to pneumonia, meningitis, hepatitis, encephalitis or anaphylaxis. In addition, the researchers found evidence that the vaccine can cause purpura in children between the ages of 11 and 17.
The researchers also examined combinations of vaccines and found that they did not increase the risk of leukemia. In fact, one study from Texas suggested that vaccines may reduce the risk of acute lymphoblastic leukemia.
In sum, "evidence was found for an association of several serious AEs (adverse events) with vaccines; however, these events were extremely rare," the researchers wrote. "Our findings may allay some patient, caregiver, and health care provider concerns."
A commentary also published in Pediatrics underscored that point.
"Fortunately, the adverse events identified by the authors were rare and in most cases would be expected to resolve completely after the acute event," Byington wrote. "This contrasts starkly with the natural infections that vaccines are designed to prevent, which may reduce the quality of life through permanent morbidities, such as blindness, deafness, developmental delay, epilepsy, or paralysis and may also result in death."