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Tylenol May Reduce Effectiveness Of Vaccines


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by Heidi Hauser Green
November 05, 2009

It is not easy watching your child receive the usual vaccinations. Shots hurt when they’re given, and your child’s discomfort might well last longer than that brief jab. The immune response triggered by many vaccines can cause irritability, soreness, fatigue, loss of appetite, and even fever. Fever might lead to seizures. No one wants their child to go through all that.

It’s natural to want to do all you can to make sure your child’s immunizations are as easy as possible on them. For many of us, that means giving a dose of acetaminophen (Tylenol), either at the time of vaccination or shortly thereafter. Although it might make us feel better, and it might help mitigate our children’s post-vaccine discomfort, a new study asks us to hold off on the Tylenol.

Led by Dr. Roman Prymula, a research team in the Czech Republic looked at data collected from hundreds of infants during two consecutive studies (primary and booster). The researchers were able to randomize whether or not participants received Calpol (paracetamol, a Tylenol-like painkiller and fever reducer sold in Europe) routinely within 24 hours of vaccination and to assess what impact it had on fevers and immune response.

They found that, although children who received painkillers did have a significantly lower risk of fever, their immune system response to the shots was also diminished. This raises some concerns about the effectiveness of vaccinations when coupled with Tylenol or similar products.

Dr. Prymula and his colleagues conducted two consecutive (primary and booster vaccination) randomized, controlled, open-label studies at ten health centers in the Czech Republic between September 2006 and April 2008.

The studies involved healthy infants with no indications of seizure risk who were between the ages of 9 and 16 weeks old at the time of initial vaccination and between 12 and 15 months old when they received their booster. The children were vaccinated against polio, pneumonia, meningitis, whooping cough, tetanus, hepatitis, and other childhood diseases. In total, 459 children were enrolled in the study. Approximately half (226) received Tylenol and the rest (233) did not.

Parents and caregivers completed diary cards on the day of vaccination and for three days afterward, noting symptoms such as pain, redness, swelling at the injection site, temperature, irritability/fussiness, drowsiness, loss of appetite, diarrhea, and vomiting. Some adverse events were also tracked for 31 days and six-month periods, depending upon the severity of reaction. Symptom severity was assessed by study physicians.

In addition, blood samples were collected before the first dose and one month after the initial vaccination, as well as before and one month after the booster dose. Blood samples were analyzed for immune response to the administered vaccines.

As expected, babies who received the painkiller were significantly less likely to develop a fever than those who did not. Just 42 percent of the babies who had paracetamol developed fevers, compared with two-thirds (66 percent) of those who did not. Very few babies in either group developed high fevers.

Perhaps unexpectedly, though, results of the blood tests from the babies who received the painkiller showed lower rates of protective antibody levels from several vaccines. Levels remained significantly lower in this group after booster vaccines several months later. In fact, even when babies who had received the painkiller during the initial shots did not receive it during the booster, their immune response was significantly lower.

Dr. Robert Chen and two other physicians from the U.S. Centers for Disease Control and Prevention (CDC) note in an editorial published in the same journal issue that this study, taken along with earlier, research, makes “a compelling case against” routine use of fever-reducing medication during vaccination. Given that very few children develop high fevers after receiving vaccines, skipping the medications unless a fever develops may be advisable.

This study’s results seem consistent with those from ten similar studies, which suggested that using such a painkiller to prevent fevers at the time of vaccination may limit children’s immune system response. However, this study cannot tell us if the immune response is similarly reduced by Tylenol administered to reduce fevers after they develop.

In addition, we cannot know the magnitude of the effect of the limited immune response on individual children, since more than 90 percent of the children in the study achieved protection from the vaccines after the booster dose.

Always discuss the risks and benefits with your child’s doctor. If your pediatrician fails to keep up with the latest studies, though, that might not help. Unless our children are at high risk for seizures, this study suggests that the best thing we can do for them may be to find non-medicated ways to help them through the hours immediately following their immunizations. According to this study, we should reach for Tylenol only if a fever develops.

Coincidentally, my 2-year-old was due for his latest shots just two days before this study came out. The pediatrician offered the standard dose of Tylenol at the time, but the nurse forgot to bring it along with the shots and my son dislikes doctor’s offices so much that waiting for it seemed unreasonable. He fell asleep in the car and continued sleeping when I brought him into the house. As it turned out, he didn’t get Tylenol after those shots. Who knows? Maybe his immune system is the stronger for it.

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