Over the years, immunization has saved millions of lives and prevented hundreds of millions of cases of disease. Today in the United States, children routinely get vaccines that protect them from 14 diseases, all of which, at one time or another, were a serious threat to our country’s children. For instance, diphtheria used to be one of the most dreaded of childhood diseases, killing more than 10,000 Americans each year, but today’s doctors are likely to never see a single case. And smallpox, which was one of the most devastating diseases the world has ever known, has been eradicated from the Earth thanks to vaccination.
Most children do not have adverse reactions to vaccines, and for those who do, they are usually mild, like soreness or swelling at the injection site or a low-grade fever. Many parents try to spare their children, especially babies, from the discomfort by giving them acetaminophen right before or after the vaccination, a practice recommended by some doctors. But Czech scientists say that while acetaminophen does prevent post-vaccination fever, it may also reduce the effect of the vaccine.
To determine the effect of acetaminophen on fever and on the immunogenicity of vaccines, Roman Prymula, of the Czech University of Defence in Hradec Kralove, and colleagues conducted two randomized controlled trials; one for the initial vaccine and one for the booster shot. The trials involved 459 healthy babies, 9 to 16 weeks old, who were getting routine vaccines against pneumococcal disease, Haemophilus influenzae type b (Hib), diphtheria, tetanus, whooping cough, hepatitis B, polio and rotavirus. Half were also given acetaminophen every six to eight hours for 24 hours after vaccination, while the others received only the vaccines.
The team found that babies given acetaminophen had a significantly lower rate of fever after both the initial vaccine (42 percent vs. 66 percent) and the booster shot (36 percent vs. 58 percent). And, according to the concentration of antibodies in their blood, the acetaminophen group also had a “significantly lower” immune response. However, when the researchers analyzed other vaccine studies, they found that the effect of acetaminophen on antibody levels was much smaller when given after the vaccination when a fever had already developed.
Vaccines are made from the same germs that cause disease, but in a killed or weakened form, that prod the immune system to make antibodies. After destroying the vaccine germs, the antibodies stay in your body and provide protection against the real disease—immunity. Fever after a vaccine is a natural part of the body’s immune response. The researchers say that because acetaminophen reduces the fever, and thus the interactions between immune cells, the body makes fewer antibodies, which would explain the reduced effectiveness of the vaccines. “The interference of paracetamol (acetaminophen) on antibody responses could result from the prevention of inflammation,” the study authors wrote.
In an editorial accompanying the study, Dr. Robert T. Chen of the CDC and colleagues proposed another explanation. “Despite being an inhibitor of cyclo-oxygenase 2 (COX-2), (acetaminophen’s) anti-inflammatory activity is contested, perhaps related to inhibition of activity in high-peroxide environments that are common at sites of inflammation,” they wrote, adding that regardless of the mechanism, the findings “present a compelling case” against the routine use of acetaminophen during childhood immunizations. “This point has implications, especially for Haemophilus influenzae and pneumococcus, for which higher and sustained antibody concentrations are needed to interrupt the carrier state and reduce transmission within the population, and for pertussis, the bacterial vaccine-preventable disease that is the least well controlled.”
That brings up a very important question: What about the H1N1 flu vaccine? Dr. Marc Siegel, an infectious disease expert and associate professor of medicine at New York University School of Medicine in New York City, says that because the immune response from the H1N1 vaccine has been so robust, giving an infant acetaminophen before the shot “may not be a problem.”
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