Pentavalent Vaccination and the Infant Mortality Rate
22 February 2013
The rapid response section of the BMJ promises to publish anything that contributes to the discussion. Repeating what I have said previously does not contribute anything new, but I hope I can clarify some of the points Dr Fleggs brings up in his last posting.
The comparison with IMR
The Pentavalent vaccine is being promoted in many Asian countries to reduce mortality in children. I wrote (posted 19/2/13) that the vaccine increases mortality and that the mortality in the immediate post vaccination period of babies who receive the vaccine, was double the IMR. A more accurate calculation will suggest that mortality is quadrupled but I selected to use the underestimation purely for pragmatic reasons and ease of explaining.
About half of the deaths that occur in the first year of life (IMR) happen in the first month - in the neonatal period. Of the IMR of 14 per 1000 live births, about 7/1000 is neonatal mortality. The other 7 deaths per 1000 occur in the remaining 11 months of the first year of a baby’s life and constitute what can be called the ‘post-neonatal IMR’. As Pentavalent vaccine is administered after 6 weeks, it is administered to babies who have survived the neonatal period. The correct comparator is this post-neonatal IMR. We used this post-neonatal IMR for the Poisson probability calculations mentioned in my bmj blog (http://blogs.bmj.com/bmj/2012/12/21/jacob-puliyel-on-the-pentavalent-stu...). The immediate post pentavalent vaccination mortality is actually 4 times as high as the expected mortality for babies who have survived their neonatal period.
The comparison with SIDS
Pentavalent vaccine is given to healthy babies. Mothers in Kerala don’t bring very sick children for immunization. Each baby is examined by health care personnel before vaccination. Surely these babies are not unconscious with meningitis or babies with sepsis and MODS.
The post-neonatal mortality-rate is mostly made up of the death of sick children. All those deaths are continuing in the background. When we speak of the immediate post pentavalent deaths, it is death in healthy babies who no one anticipates will die in the next few hours. When such unexpected and unexplained deaths occur (and they do occur ‘normally’ but very rarely) they are classified as SIDS deaths. We used the SIDS mortality as the comparator for this reason and calculated that the post pentavalent death rate in Kerala was 70 times higher than the US SIDS rate. We do not have figures for the SIDS rate in Kerala prior to introduction of Pentavalent vaccine, but the SIDS rate (unexplained deaths) cannot in any case be larger than the IMR (explainable + unexplained deaths).
The comparison with nationwide 'India IMR'
Kerala is not the richest state in the country. However through the empowerment of women, improved female literacy, along with the tradition of matrilineality in some communities and other sociopolitical factors, Kerala has one of the lowest IMR figures in the country.
Dr Flegg suggests that the immediate post vaccination mortality in Kerala must be compared to the India IMR of 50/1000. This implies that Kerala must continue vaccination with Pentavalent vaccine till the IMR rises from 14/1000 to 50 /1000 (and perhaps a little higher to achieve statistical significance?). Not many people in Kerala will applaud that suggestion.
Competing interests: The author comes from Kerala and admits to a possible pro-Kerala bias