A new study has demonstrated that administering prophylactic acetaminophen to babies receiving immunizations may blunt their immune response and dampen the development of protective antibodies. (Prymula R, et al. Effect of prophylactic paracetamol administration at time of vaccination on febrile reactions and antibody responses in children: two open-label, randomised controlled trials. Lancet 2009;374[9698]:1339-50)
This finding calls into question the long-standing recommendation from the US Advisory Committee on Immunization Practice: “…it is reasonable to consider administering antipyretics (such as acetaminophen) at age-appropriate doses at the time of vaccination and every 4 – 6 hours for 48 – 72 hours to children at higher risk for seizures than the general population.”
Since it has never been easy to predict which children will suffer from febrile seizures, physicians have tended to advise that all parents give prophylactic doses of fever-controlling medications to children who are about to receive routine immunizations.
Besides, administering antipyretics not only helps to prevent febrile seizures, but it also presumably helps to control pain and otherwise improve a child’s well being after vaccination.
Vaccinations Induce Immunity to Potentially Dangerous Diseases
Immunity to any foreign antigen normally develops after one’s first exposure to the antigen. Although a clinically apparent syndrome – which often includes a fever – may result from that initial exposure, the immune system usually “catches up” with the invader, eliminates it, and acquires the ability to “remember” it.
Thereafter, immune memory quickly boosts the body’s response with each subsequent exposure and forestalls the development of overt illness.
For example, prior to the development of a vaccine for chickenpox, this disease was a universal childhood experience. Everyone who was exposed to the virus fell ill a week or two later, suffered through the fever and the characteristic rash, and – in most cases – recovered 10 to 14 days afterward.
Once a person with a healthy immune system caught chickenpox, immune memory prevented the disease from recurring, despite multiple exposures to the virus in the ensuing years.
Vaccines essentially introduce one’s immune system to weakened or killed foreign antigens. This allows immunity to develop without causing full-blown clinical illness.
So, why should controlling a child’s fever lessen his or her immune response to a vaccination?
Fever is an Important Part of a Normal Immune Response
Fever occurs when certain areas in the brain are stimulated by cytokines and other chemicals in the bloodstream. Cytokines are messenger molecules produced by immune cells (natural killer cells, T helper cells, macrophages, T suppressor cells, etc.) whenever a foreign antigen is recognized.
Transfer factors, interleukins, interferons, tumor necrosis factors, growth factors, and chemokines are among the many cytokines that have been described.
Cytokines serve to alert other cells to the invader’s presence and help to enhance – or suppress – immune activity. The immune response is a highly complex process; a given cytokine may serve a multitude of purposes, depending on which cells it stimulates and the specific timing of its production.
Fever is not merely a superfluous response to inflammatory cytokines. Increased body temperature is instrumental in propagating the immune response: The increased heart rate and vascular dilation that accompany fever help to carry immune cells into the tissues more quickly, and some immune cells may function more efficiently at higher ambient temperatures.
Thus, rather than being a disease entity which must be treated, fever is an important arm in the protective cascade that leads to antigen recognition, immune response (lymphocyte induction, antibody production, etc.), immunomodulation (i.e., “calming” the immune response when the invader has been eliminated), and immune memory.
While it is still important to attempt to identify and protect those children who are at risk for febrile seizures, and while it still isn't clear if the immune response is blunted by treating fevers that have already occurred, the widespread practice of using drugs to prevent vaccine-induced fevers should be questioned.
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