Protective efficacy of a monovalent oral type 1 poliovirus vaccine – Authors' reply

Abstract

Jacob Puliyel and colleagues highlight the importance of ensuring appropriate ethical standards are adhered to in the course of scientific studies. In our study of the field efficacy of monovalent oral type 1 poliovirus vaccine (mOPV1) we analysed existing surveillance data from acute flaccid paralysis (AFP) cases collected since 1997. The vaccines assessed were licensed for administration in India by the national regulatory authority the Drugs Controller General of India. The mOPV1 formulation assessed in our study has been used since mid-2005 by the Government of India and now in over 20 countries around the world. The absence of interference from types 2 and 3 particularly type 2 seems to be the reason for the three-fold greater efficacy per dose of mOPV1 against paralysis from type 1 wild poliovirus compared with trivalent vaccine in northern India. To clarify the background to the increase in cases of AFP in recent years noted by Puliyel and colleagues this is the result of a deliberate effort that began in 2004 to intensify surveillance and reporting as India pushes to eradicate polio. The increase in AFP cases began before mOPV1 was introduced and occurred across India including states where mOPV1 has not been used. The introduction of mOPV1 is not therefore the cause of the increase in cases of AFP. The National Polio Surveillance Project continues to monitor cases of vaccine-associated paralytic poliomyelitis (VAPP) which typically occur at a rate of two to four cases per million birth cohort immunised with trivalent oral poliovirus vaccine. The postmarketing surveillance of mOPV1 that was implemented as part of its licensing has not detected any increase in the proportion of AFP cases with VAPP in areas where this vaccine has been used. (excerpt)