Giving babies paracetamol after vaccination to prevent fever may make the vaccines less effective, researchers say.
In a trial of 450 babies, paracetamol taken in the 24 hours after vaccination did reduce fever. But the Czech researchers found a significant drop in the response to the vaccine when the painkiller was used. A UK doctor said the study, published in The Lancet, was a reminder not to give children medicines without good reason.
"Paracetamol was being given to ease parents' fears that their children would get a high fever after vaccination," said Professor Roman Prymula. But the trial, in children receiving routine vaccinations and boosters, found that this practice may do more harm than good.
Half the children were given paracetamol every 6 to 8 hours after vaccines against pneumococcus, Haemophilus influenzae type b, diphtheria, tetanus, whooping cough, hepatitis B, polio and rotavirus; the other half were given nothing. 42% of the children given paracetamol had a fever of 38 °C or more after the first vaccinations, compared with 66% of those who weren't, with similar results after the boosters.
But when the researchers looked at the response to the vaccines, antibody levels were lower in the children who had taken paracetamol, suggesting that the immunity the vaccines are meant to give was weaker.
Interfering with immunity
This is thought to be the first time such interference has been shown. One explanation, the researchers say, is that paracetamol interferes with the immune cells' response to the vaccine. "The clinical importance of these findings is unknown and needs further evaluation," Prymula said, "but giving paracetamol as a preventive measure at vaccination should not be routinely recommended without carefully weighing the expected benefits and risks."
Dr David Elliman, a child immunisation expert at Great Ormond Street Hospital, said he didn't know how common it was to give paracetamol after vaccination, but he had always told parents it wasn't needed. "My advice is: if a child has a fever, don't always assume it's because of the vaccine. But if the child is well otherwise, ask yourself whether there is really a need to bring the temperature down. Giving paracetamol before or after vaccines shouldn't be encouraged: first, there is little benefit, and second, these early data suggest it may do harm."
A Department of Health spokeswoman said some children may develop a mild fever after vaccination, and the department's advice is to give infant paracetamol or ibuprofen only to treat a fever. "The results of this study don't conflict with that advice."
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