International Journal of Epidemiology 2001;30:1034
© International Epidemiological Association 2001
Infectious Disease |
Commentary: Cuba libre de poliovirus
Aventis Pasteur, 4650 Wismer Road, Doylestown, PA 18901, USA.
In this issue of the International Journal of Epidemiology, Mas Lago et al.1 report the disappearance of oral polio vaccine (OPV) strains from Cuba following a national vaccination campaign, and infer from their results that OPV could be safely discontinued after polio eradication without fear that revertant viruses would continue to circulate and cause polio.
The public health successes accomplished by Cuba with regard to polio and other vaccine-preventable diseases are admirable and deserving of praise. However, there are a number of reasons to hesitate before extrapolating the polio results to other countries.
First, the search for persistent virus was conducted in an age group not ideal for the purpose: infants less than 8 months. It seems unlikely that infants who do not walk and who have little direct contact with older children would acquire infection, even if there were still excretors in the community. Evidence for this objection is found in the authors' own data. They show an absence of seroconversion among these infants, despite the probability that some of them were exposed to siblings who excreted attenuated polio virus in the weeks after the national campaign.
With regard to the issue of continued circulation of these strains, tests in 1–3-year-old infants would have been more interesting.
Second, no search for poliovirus in sewage is reported here. Although Mas Lago et al. tested over 800 infants, persistent excretion may be even rarer, and the 800 infants presumably included none with B cell immunodeficiency. Sewage testing screens larger populations.
Third, the Cuban population is already highly immune to polio, which would limit the spread of excreted OPV strains. The recent outbreak reported from nearby Hispaniola, where a type 1 revertant became epidemic in a poorly vaccinated population,2 and similar episodes in Egypt and China,3 lead to the conclusion that attenuated strains will re-acquire neurovirulence if given the opportunity for multiple passages in the human intestine.
Thus, although the data from Cuba are encouraging for that nation, and perhaps for other countries with reasonably high hygiene and public health infrastructure, they do not allow us to conclude that abrupt discontinuation of OPV, without other measures, will avoid resurrection of paralytic polio due to vaccine strains. More studies are needed before this pos-sibly dangerous strategy, which will allow rapid accumulation of susceptibles in the possible presence of virulent virus, is adopted.
References
1
Más Lago P, Cáceres VM, Galindo MA et al. Persistence of vaccine-derived poliovirus following a mass vaccination campaign in Cuba: implications for stopping polio vaccination after global eradication. Int J Epidemiol 2001;30:1029–34.
2 Centers for Disease Control. Outbreaks of poliomyelitis—Dominion Republic and Haiti, 2000. MMWR 2000;49:
3 Circulation of a type 2 vaccine-derived poliovirus, Egypt, 1982–1993. MMWR 2001;50:41–42,51.[Medline]
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