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.
It’s common for parents to give their kids Tylenol just before or immediately after a vaccine is administered to prevent fevers and crankiness.
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.
The study, which was led by military and government scientists in the Czech Republic 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 — 42 percent versus 66 percent of the others — and very few in either group developed a high one.
However, lower rates of protective antibody levels from several vaccines were seen in the group given the drug. Levels remained significantly lower in this group after booster vaccines, given when the babies were 12 to 15 months old.
Next, the researchers looked at 10 other vaccine studies and found some supporting evidence that using Tylenol to prevent fevers at the time of vaccination may curb immune system response rates. The same may not be true of using the drug to treat fevers after they develop.
The CDC doctors also point out that even with the fever-lowering drugs, more than 90 percent of children in the Czech study achieved protection from the various vaccines after the booster dose, so the effect of lower levels of antibodies on any individual might be small.