Let me first say that I firmly believe the decision to vaccinate is a personal one. No one should be mandated to do so by anyone. Importantly, this decision should be an informed decision and sadly far too many parents aren’t given any information of any use when it comes to what they should do regarding vaccines. Any post on vaccines here isn’t to sway you one way or another, but is simply there to provide information that I can find on the various topics that will help you make the decision that you feel most comfortable with. In this vein, I want to talk about something that rarely, if ever, is discussed when people talk about the pros and cons of vaccination – breastfeeding. While many people are aware of the benefits to the immune system that breastfeeding offers (see Why Is Saving Babies Lives Not Enough? and 2 B’s and the Big C), many people are not aware that breastfeeding also has important implications for vaccinations.
If you start doing research on vaccines, one of the things you’re told about each and every one is that your child will be immunized by getting the shots. If that weren’t the case, why bother getting them? And yet, the truth is that not all children will become immune to the diseases for which a vaccine is given. For example, the varicella vaccine (chickenpox) has a reported effectiveness of approximately 87%, the effectiveness of the mumps component of the MMR vaccine has been found to be as low as 69%, and the effectiveness of the pneumococcal vaccine fares well at 94-97%. One factor many parents are unaware of is the role of feeding type in their children to the immunological response to certain vaccines. Is it really possible that how we feed our kids can affect how our body responds to a vaccine? Turns out the answer is ‘yes’ and below I’ve outlined the research on the matter for the most common childhood vaccines.
In a study out of Sweden examining the antibody response to the PCV vaccine (serotypes 6B and 14), the authors compared children who had been breastfed for more or less than 90 days. The children who did not reach the required antibody response for the PCV serotype 6B were nearly all breastfed less than 90 days (with the exception of 1 case) and at 6 months of age, children from the longer breastfeeding group had greater protection against serotype 14.
Haemophilus influenzae type B (Hib)
The same authors from Sweden who examined the PCV vaccine also examined the Hib vaccine as the two are administered together in Sweden (and elsewhere). These authors found that of the children who did not reach the minimum antibody response for the Hib, 100% had been breastfed less than 90 days. In a separate study out of Canada, the comparison was done between breastfed and formula fed infants with similar results. At both 7 months and 12 months, infants who were breastfed had significantly greater antibody levels than the infants who were formula fed. A more recent study also suggests that the immune response to the Hib vaccine is more pronounced in infants breastfed less than 6 months compared to those breastfed greater than or equal to 6 months.
The diphtheria, tetanus, and pertussis vaccine is given at multiple time points, but results of a comparison between breastfed and formula fed infants on the effectiveness of the three components at both 3-4 months of age and 21-40 months of age found that at all time points and for all components of the vaccine, breastfed babies showed a greater antibody response. Importantly, this research also examined two types of formula: conventional and low-protein (to mimic breastmilk) and found that the benefits of breastmilk were greater than either type of formula. And while the two formula types were nearly always equal, the low protein formula group showed a better response to the poliovirus than the conventional formula group (but again, both showed a reduced efficacy compared to the breastfed group). This finding was confirmed in another study, but others have apparently not found a significant difference by breastfeeding method (though the studies cited by Wold and Adlerberth are unavailable to me online and thus I am unable to ascertain if there is another reason why they might not find any statistically significant differences).
The evidence of feeding type on the MMR vaccine is interestingly mixed. In a study from Canada, researchers found that the response to the MMR vaccine from breastfed infants was significantly better and more targeted than that of formula fed infants. In fact, in their findings, only the breast-fed infants showed an increase in certain cells associated with an appropriate immunological response. However, other authors have pointed out that in this study, the level of measles plaque neutralizing antibody was lower in breastfed infants, suggesting the opposite of what the authors initially reported and found with respect to other measures of antibodies in the system. Interestingly, the reason for lower neutralizing antibodies with live viruses in breastfed infants is due to the fact that the virus was unable to replicate in the gut and the “enhanced clearance of virus… due to anti-viral secretory IgA antibodies and other factors in breast milk”. So even when the argument is made that formula-fed infants can show an increased immune response, it’s only because of the better general immune response of being breastfed.
One early study from the 1970s found no effect of bottle feeding or breastfeeding on the efficacy of the poliovirus vaccine. This was replicated in a more recent study which included duration of breastfeeding (less than six months versus greater than or equal to six months) as a factor of interest in the efficacy of the polio vaccine.
One meta-analysis has combined the research and found an adverse effect of breastfeeding on the efficacy of the oral rotavirus vaccine. When studies were combined, only 48% of breastfed infants showed signs of immunity whereas 70% of formula-fed infants demonstrated immunity responses. However, a later analysis found that the adverse affects of breastfeeding were generally non-significant and could be countered by administering 3 doses of the rotavirus vaccine instead of 1 (whether or not this is deemed too many shots is entirely up to you).
I could not locate any studies that examined the efficacy of the Hepatitis A vaccine by feeding method.
I could not locate any studies that examined the efficacy of the Hepatitis B vaccine by feeding method.
While there’s no one conclusion that can be made for the role of feeding type with vaccinations, some general conclusions (plural) are warranted. First, for non-live vaccines, there is evidence that breastfeeding enhances the immunological response for infants. That is, a breastfed child has a better chance of reaching the threshold necessary to say they are “immune”. This doesn’t mean that formula-fed infants won’t reach it, but that a greater proportion won’t. Second, in some cases (e.g., PCV, Hib) even the duration of breastfeeding seems to have an effect on the immune response, with longer breastfeeding being related to better immunity. Third, the results for live vaccines (e.g., MMR) seem less conclusive. While some research suggests a better immune response for breastfed babies, others suggest the opposite. Interestingly, the research that suggests a better immune response for formula-fed babies acknowledges that the reason seems to be that breastfed babies somehow remove the live virus from their systems more efficiently (without developing the full antibodies). To me, this suggests that the system of the breastfed baby is generally healthier and better able to handle infection (I’m sure raising the question for some about the utility of the vaccines in these cases, but remember the vaccine is a tiny dose relative to the actual disease).
In short, while the immunological response is high for all infants, it’s not perfect, and there does seem to be an effect of feeding type. Parents should know of this and factor this information into their decision about whether or not to vaccinate their child. After all, vaccination doesn’t happen in a vacuum and the more information parents have, the better they can feel about whatever decision they make.
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