Tylenol lowers vaccine immunity when given to babies

by Marilynn Marchione
AP Medical Writer

Giving babies Tylenol to prevent fever when they get childhood vaccinations may backfire and make the shots a little less effective, surprising new research suggests.

It is the first major study to tie reduced immunity to the use of fever-lowering medicines. Although the effect was small and the vast majority of kids still got enough protection from vaccines, the results make “a compelling case” against routinely giving Tylenol right after vaccination, say doctors from the U.S. Centers for Disease Control and Prevention.

They wrote an editorial accompanying the study, published in the British medical journal Lancet.

The study only looked at preventive use of Tylenol – not whether it is OK to use after a fever develops.

Tylenol or its generic twin, acetaminophen, is recommended widely as a painkiller for babies. Many parents give it right before or after a shot to prevent fever and fussiness, and some doctors recommend this. The CDC’s vaccine advisory panel says it is a reasonable thing to do for children at high risk of seizures, which can be triggered by fevers.

However, fever after a vaccine isn’t necessarily bad – it’s a natural part of the body’s response. Curbing fever, especially the first time a baby gets a vaccine, also seems to curb the immune response and the amount of protective antibodies that are made, the new study found.

It was led by military and government scientists in the Czech Republic and was done at 10 medical centers in that Eastern European country. It involved 459 healthy infants, 9 to 16 weeks old, who were getting vaccines against polio, pneumonia, meningitis, whooping cough, tetanus, hepatitis and other childhood diseases.

Half were given three doses of Calpol, or paracetamol – a Tylenol-like brand sold in Europe – during the first day after vaccination. The others were given nothing besides the vaccines. Babies given the painkiller were significantly less likely to develop a fever, but lower rates of protective antibody levels from several vaccines were seen in that group.