Vaccinations

Probably nothing raises more anxiety and more questions during pregnancy than vaccinations.

As pointed out in our chapter on medications, we try to maintain a balance between two general principles.  These are the principles of avoidance and of comparative risk.

The principle of avoidance means that if you can safely avoid getting a particular vaccine while you are pregnant, you should probably do so.  Sometimes a simple change of itinerary will accomplish this.  For instance, whether you need a yellow fever shot when traveling between two countries often depends on which country you visit first.  Or which part of a country you will be visiting.  Similarly, not staying overnight in an area that has pigs and rice paddies will probably mean you don’t need shots for Japanese Encephalitis.  Often, with the yellow fever vaccine, the need for the shot is more for political reasons than for medical ones.  If you are truly not going to be exposed to the disease, you may be able to get a waiver to avoid getting the shot.

The second principle is that of comparative risk.

Remember that, despite some theoretical risks, there are no currently available vaccines that are of proven risk to a developing baby.  On the other hand, many of the diseases we are trying to prevent are clearly harmful to the fetus and may even cause its death.  Therefore, if there is no way to avoid exposure to a given disease, then the vaccine is definitely the lesser of two evils.  What I often tell my patients is, “I cannot guarantee that this vaccine will not hurt your baby.  But I can promise you that if you don’t take it, that will hurt your baby.”

There remain, however, two concerns regarding the use of vaccines. 

One is that some vaccines may cause a fever.  There is some evidence that an rise in body temperature during pregnancy increases the risk of neural tube defects.  The risk is miniscule, however, and appears to be prevented by simply taking adequate prenatal vitamins (i.e. those containing at least one milligram of folic acid.)  We would say that if there is a true risk of exposure to the disease, the vaccination is warranted.

The other concern is whether or not the vaccine will be effective.  As we point out elsewhere, pregnancy is a relatively immune suppressed state.  There is concern, therefore, that vaccination may not produce an adequate immune response.  There was previously evidence that this might be the case with yellow fever vaccine and perhaps with Hepatitis A vaccine.  More recent studies seem to show that these vaccines are perfectly effective during pregnancy.  Even if not, however, when exposure is unavoidable, some protection is probably better than none.

The vaccines that raise the most concern during pregnancy are the “live virus” vaccines.  These include vaccines against mumps, measles, rubella (MMR), varicella and yellow fever.  The fear is that these viruses may cross the placenta and cause disease in the fetus.  There is not enough evidence to clearly state that these vaccines are safe in pregnancy and, if possible, their use should be avoided.  MMR vaccines have, however, been inadvertently given to many pregnant women over the years and no ill effects have been reported. A similar case exists for the use of yellow fever vaccine, and to a lesser extent with varicella vaccine.  Thus if you are not immune to these diseases and cannot reliably avoid exposure to them, the vaccine is probably preferable to the risk of getting these diseases as the viruses in question are definitely harmful to the developing fetus.

The only other “live” vaccines are those against cholera, traveler's diarrhea and typhoid.  These contain live but weakened strains of the causative bacteria.  As these vaccines may have gastro-intestinal side effects such as nausea, cramps and diarrhea, and pregnancy is often already fraught with gastrointestinal problems, we prefer not to use them in pregnancy.  There is a perfectly acceptable injectable typhoid vaccine that can be used instead.  There are also other simple preventive measures against diarrhea and very few travelers actually become exposed to cholera, so we have not advocated the use of these vaccines.

A tetanus/diphtheria shot is definitely recommended in pregnancy if you haven’t had one in ten years.  So is a flu shot.

Vaccines composed of inactivated or recombinant viruses are generally considered safe in pregnancy and in some cases are routinely recommended during pregnancy.  These vaccines include hepatitis A and B, injectable polio vaccine, rabies and Japanese Encephalitis (JE).  The JE vaccine has enough other side effects, however, that it should not be given unless absolutely necessary.

“Gamma globulin” is rarely needed during pregnancy but its use, when indicated, is generally considered safe.  The most likely event in which you would need this is if you were exposed to rabies.  In that case, the risk from the rabies is so high as to warrant almost any protective measures.