Does giving a baby Tylenol after a vaccination dampen their immune response and make the vaccine less effective? How does Tylenol reduce inflammation and fever without making a shot less effective?
—Dewey user
This is a question without an obvious answer, but we can put out the facts and then think about what they mean.
Fact 1: About half of babies will develop a fever after immunizations. This isn’t dangerous, but as every parent knows, your baby with a fever is uncomfortable.
Fact 2: Administering Tylenol either at the same time or immediately after vaccination reduces this chance of fever to about 25% (highly significant in a meta-analysis of randomized trials).
Fact 3: Administering Tylenol seems to lower the antibody response to the vaccine; infants who received Tylenol as prophylaxis had fewer antibodies later. However: generally the level of antibody development is sufficient to prevent disease in all groups. So it is unclear whether the lower antibody levels are clinically relevant.
What this means is there is both a benefit to the Tylenol (lower fever) and a cost (lower antibodies). Both sides of the coin are fairly minor — the reduction in fever risk is reasonably sizable, but fever isn’t necessarily a problem. The reduction in antibodies is small and not obviously of relevance.
Either choice seems fine. The common advice here, which I think is sensible, is to initially not give Tylenol but then to give it if your child does seem to be uncomfortable. You’re taking a small gamble that you’ve got an hour of fussiness while they wait for the dose to kick in, but only a small one.
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