Immunization Fever

(Image from the Mid America Immunization Coalition)

Almost thirteen years ago I took my baby girl to get her immunized and the nurse told me that if she got a fever I could give her some children's Tylenol. I don't remember if she got that fever or not but I've heard other moms complain about it. Why would something that's supposed to keep my baby healthy make her sick?

The answer lies with the way the immune system works and the way a vaccine works. When you get sick your immune system fights the illness and keeps a record of it so that the next time you are exposed to that illness it can fight it better, and maybe even keep you from getting sick at all. This record is really a recognition of the outside coating of the organism that made you sick. One way to keep people from getting dangerous viral diseases is to give them injections of the outside coating part of the disease causing microbe. The immune system can then recognize the intruder and make its record without the person having to be really ill.

So what about that fever? Does this mean there were some live organisms that made it into the injection? Not at all. Fever is caused by the immune response. The high temperatures are part of the body's mechanism for fighting off intruders. When you get an immunization your body doesn't know that the microbes are dead. All it knows is that it found some foreign stuff in your blood, so it starts the process of fighting the intruder off.

Knowing how uncomfortable the fever makes babies, and how scary that is for their families, some scientists in the Czech republic were wondering if it would be okay to just give all of the infants some Tylenol when they got their immunizations. It turns out that the Tylenol made the babies' immune systems not work quite so well. This means that nurses will probably keep giving the same advice and some babies will keep getting the fever and will then need to be given medicine for it. It's still a lot safer than not giving them their immunization.

Links:

A summary of the article from The Lancet

A more in depth description of how vaccines work

Word of The Day

Antigen: a chemical on the outside of cells and viruses that the body can recognize and use to determine if the cell or virus came from outside of the body.