Print version ISSN 0042-9686
Bull World Health Organ vol.80 n.12 Genebra Jan. 2002
Further clarity on vaccine-associated paralytic polio in India
Editor We appreciate the comments by T.J. John in response to our article on vaccine-associated poliomyelitis (VAPP) in India (1). He highlights some of the methodologic challenges in deriving risk estimates of this type and correctly points out that interest is now shifting from risk estimation to estimation of VAPP burden in terms of numbers of children paralysed because of exposure to oral poliovirus vaccine (OPV).
The primary purpose of our analyses was to provide risk estimates of VAPP in India under conditions of massive use of OPV by applying established methods of calculating VAPP risk (24). We used exactly the same methods and definitions outlined in reference 2 to allow risk calculations that would be comparable among different populations.
Our findings demonstrate that the risk of VAPP is lower in India compared to previous analyses in Latin America (2) or in industrialized countries (3, 4). Since we reported our findings, surveillance data from India for 2000 and 2001 have become available. These data show a decreasing trend in the total number of VAPP cases from 181 in 1999, to 129 in 2000, and 109 in 2001, suggesting that the 1999 data (and associated risks) were not stable. Massive exposure to more than 750 million doses of OPV in India in 1999 alone probably resulted in a "catch-up phenomenon" exposing many children to the first "immunizing" dose of OPV, with the associated increased risk of VAPP. Only data from subsequent years will allow calculation of a more precise VAPP estimate under conditions approximating a steady state in India.
Thus, we are confronted with a situation where the risk is exceedingly small, but the total number of VAPP cases is increasingly of concern. We believe that the established methods of calculating VAPP risk estimates will continue to have their utility, and should not be abandoned. However, the total number of VAPP cases that communities will have to bear in an increasingly polio-free world (5) may be driving polio vaccination policy decisions to a much greater degree. To assist the process, The World Health Organization is committed to preparing an estimate of the global VAPP burden in the near future.
Conflicts of interest: none declared.
1. Kohler KA, Banerjee K, Hlady WG, Andrus JK, Sutter RW. Vaccine-associated paralytic poliomyelitis in India during 1999: decreased risk despite massive use of oral polio vaccine. Bulletin of the World Health Organization 2002;80:210-6.
2. Andrus JK, Strebel PM, de Quadros CA, Olive JM. Risk of vaccine-associated paralytic poliomyelitis in Latin America, 1989-1991. Bulletin of the World Health Organization 1995;73:33-40.
3. Strebel PM, Sutter RW, Cochi SL, Biellik RJ, Brink EW, Kew OM, et al. Epidemiology of poliomyelitis in the United States one decade after the last reported case of indigenous wild virus-associated disease. Clinical Infectious Diseases 1992;14: 568-79.
4. Joce R, Wood D, Brown D, Begg N. Paralytic poliomyelitis in England and Wales, 1985-91. BMJ 1992;305:79-82.
5. WHO. Progress towards the global eradication of poliomyelitis, 2001. Weekly Epidemiological Record 2002;77:98-107.
2 Epidemiologist, Polio Eradication Branch, Global Immunization Division, National Immunization Program, Centers for Disease Control and Prevention, Atlanta GA 30333, USA (email: email@example.com). Correspondence should be addressed to this author.
3 Medical Officer, World Health Organization Regional Office for South East Asia, New Delhi, India.
4 Medical Officer, Vaccine Assessment and Monitoring, Vaccines and Biologicals Department, World Health Organization, Geneva, Switzerland.