Herd Immunity


Over the past several years there has been a growing trend of parents that are terrified of vaccinating their kids citing reasons such as the debunked link to autism or that it just isn’t “natural.”   A healthcare blog run by several infectious disease doctors called Controversies in Hospital Infection Prevention has run frequent stories reporting on the declining vaccination rates as well as problems that ensue because of that, most recently about the whooping cough epidemic in Washington and wondering why Jenny McCarthy has so much influence on national views on vaccinations.

In an attempt to bring some light into the benefits of herd immunity I found a recent article that takes a look at the Seven-Valent Pneumococcal vaccine and its effects on co-colonization of other strains of Pneumococcus in children.  This study took a look the rate of co-colonization of children up to 6 years old from Portugal in groups of pre-vaccine era, vaccinated children, and unvaccinated children in vaccine era.  Despite the fact that there are well more than 7 variants of pneumococcus (as is evident by the fact that the standard pneumococcal vaccine is now 13-valent and high risk individuals are recommended to receive the 23-valent version), this study found that children vaccinated with just the 7-valent vaccine had significantly less co-colonization with other variants of the pneumococcal bacteria in nasal samples.  The biggest problem initially is in detection of so many various variants.  Using a combination of the plyNCR-RFLP and molecular serotyping microarray methods based on restriction pattern that is highly conserved among pneumococcal species, this study was able to detect co-colonization in 20% of their samples, while not great significantly higher than previous studies.  They then compared the rate of co-colonization between the three groups of children and found that co-colonization rates of non-vaccine type pneumococcal bacteria were significantly lower, only 8% in fully vaccinated children compared to 18% in the other two groups.  However, the unvaccinated vaccine era children, while displaying higher co-colonization rates, showed colonization similar to their vaccinated counterparts by displaying a decrease in colonization by the vaccine type variants.

The paper goes on to claim that the decrease in non-vaccine type pneumococcal co-colonization in the vaccinated group reflects a possible understanding of pneumococcal evolution.  It could be that decrease in some variants leads to decrease in others by preventing horizontal transmission of genes, including resistance genes.

One interesting finding was that the predominant non-vaccine types that were isolated were 6A and 19A which have been included in the 13-Valent vaccine.  It remains to be seen with the recent 13-Valent vaccine whether or not the same holds true as is seen here with the 7-Valent

However, this study in Portugal is recent as the 7-Valent Vaccine has only been available there since 2011.  What about where the vaccine has been available longer and individuals potentially have more time to be re-colonized to other variants.  A UK study looking at the long term benefits of the 7-Valent vaccine seems to think that the effects are reasonably long lasting


Valente C, Hinds J, Pinto F, Brugger SD, Gould K, et al. (2012) Decrease in Pneumococcal Co-Colonization following Vaccination with the Seven-Valent Pneumococcal Conjugate Vaccine. PLoS ONE 7(1): e30235. doi:10.1371/journal.pone.0030235

Choi YH, Jit M, Gay N, Andrews N, Waight PA, et al. (2011) 7-Valent Pneumococcal Conjugate Vaccination in England and Wales: Is It Still Beneficial Despite High Levels of Serotype Replacement? PLoS ONE 6(10): e26190. doi:10.1371/journal.pone.0026190

One comment on “Herd Immunity

  1. I think it’s silly that parents are not wanting to vaccinate their kids. If they have pets do they not get their pets vaccinated either? I know with my dogs when the vet calls and says my dogs are needing their vaccinations I make an appointment for as soon as possible. Vaccinations are meant to help, and frankly if my child’s pediatrician is telling me that a certain vaccination could my child prevent something that shouldn’t happen in their body, then that’s all the info. I need.

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