PV is a combination of the DPT vaccine and two more vaccines against Haemophilus influenza type B (Hib) and hepatitis B. Starting December 2011, PV was introduced into India's immunisation programme to replace DPT vaccine in a staged manner with a view to adding protection against Hib and Hepatitis B without increasing the number of injections given to infants.
But sporadic reports of unexplained deaths following immunisation with PV had been a matter of concern. Puliyel, Sreenivas and their colleagues undertook the study to find out if these deaths were merely coincidental or vaccine-induced.
The authors obtained data of all deaths reported from April 2012 to May 2016 under the Right to Information Act. Data on deaths within 72 hours of administering DPT and PV from different states were used.
For their study, the authors assumed that all deaths within 72 hours of receiving DPT are natural deaths. Using this figure as the baseline, they presumed that any increase in the number of deaths above this baseline among children receiving PV must be caused by this vaccine.
According to their analysis of the data provided by the government, there were 237 deaths within 72 hours of administering the Pentavalent vaccine -- twice the death rate among infants who received DPT vaccine.
Extrapolating the data, the authors have estimated that vaccination of 26 million children each year in India would result in 122 additional deaths within 72 hours, due to the switch from DPT to PV.
"There is likely to be 7,020 to 8,190 deaths from PV each year if data from states with the better reporting, namely Manipur and Chandigarh, are projected nationwide," their report says.
The authors note that while the study looks at the short-term increase in deaths (within three days of vaccination) it does not calculate the potential benefits of PV on infant mortality, for example by protection against lethal diseases like Haemophilus influenza.
In spite of the data presented in this paper from a large cohort, the authors point out that the evidence is merely circumstantial and not conclusive. "These findings of differential death rates between DPT and PV do call for further rigorous prospective population-based investigations," the study concludes.