Vaccine doubts raised after polio outbreak

A study of a l988 polio outbreak in Israel has divided experts on the efficacy of current vaccination programmes and left the rest of us more confused than ever.

Of the l5 cases of polio recorded, l2 occurred in the Hadera subdistrict, where a killed polio virus (enhanced inactivated polio vaccine, or eIPV) has been the only polio vaccine used for babies since l982. Nevertheless, nine of the l5 victims were l5 years or older and had been immunized with at least three doses of the oral polio vaccine, currently used in the UK and America.Of the l6 authors, comprised of epidemiological authorities in Israel, Switzerland and America, notably the Centres for Disease Control, one group believes that the teenagers vaccinated with the oral vaccine had a greater susceptibility because of the low dosage administered, and children injected with the inactivated virus had low gut immunity to infection. They reckon two initial doses of the killed virus, followed by several doses of the oral vaccine in a higher dosage than given previously, will do the trick.

Finally, they'd offer a third sugar cube version of the oral vaccine between ages 3 and l0. "Routine supplementary dose of OPV at school entry would boost immunity in children with marginal immunity, catch the very few who may not have been immunized in infancy against any of the three virus types, and immunize a proportion of non-immune adults by environmental spread of vaccine virus."

Group II, on the other hand, interprets the outbreak as a result of exposure to contaminated sewage. Victims in Hadera were close to the centre of the epidemic, the strain of vaccine differed from that for which the population is vaccinated and many of the victims had antibody levels too low to protect them.

This group endorses the killed virus as "the basic tool necessary to achieve, with high coverage, a uniformly high immune response which will protect vaccinees against the paralytic disease, without the two principal risks associated with OPV-vaccine failure and vaccine associated disease."

And just to confuse matters further, in a letter to The Lancet, Paul E. Slater, of the Department of Epidemiology, at the Ministry of Health in Jerusalem, argues that the killed virus will only work if you can guarantee l00 per cent uptake. The live oral virus is better, he says, because it works in the gut, it displaces the wild virus by weaker, vaccine strains and it immunizes contacts by spreading the weak vaccine virus environmentally.

Just to be on the safe side, however, Israel is combining all possible options by offering the killed virus at 2,4 and l2 months and the live virus at 4, 6 and l2 months. Any questions?