Too Many Polio Vaccines?

Proponents and opponents of live-virus poliomyelitis vaccines, which are taken by mouth, got closer to the infighting last week. All the leading scientists involved on both sides of the struggle to displace the Salk killed-virus vaccine (which must be injected) appeared at research meetings in Atlantic City and Newark, N.J., and nearly all took off the gloves. Government umpires looked on uncomfortably, dreading the day when they have to decide on licensing an oral vaccine.

Shift in Aim. Despite five years of intensive efforts to get everybody in the U.S. Salk-vaccinated (about 300 million shots have been injected), 91 million people still have not had any vaccine. And paralytic polio has been increasing for two years. From 2,500 cases in 1957 it went up to 3,700 in 1958 and 5,500 in 1959. Unaccountably, the disease has shifted its aim: young children, especially under two years old, are now the principal victims. They are concentrated in urban and. rural slums, among Negroes and Puerto Ricans. This is partly explained by the fact that vaccination has been most neglected in these groups. But a major paradox is that, because of living conditions, these were formerly the groups in which harmless natural infection occurred most often, making paralytic disease rare. One suggestion: the wild viruses may be changing their way of life. The only thing certain is that polio is far from having been defeated.

Why? Three doses of Salk vaccine are only 80% to 90% effective in conferring immunity, said two U.S. Public Health Service experts. Advocates of live-virus vaccines maintain that their preparations, taken in one or three doses, confer immunity in 90% or more of the vaccinated, as measured by laboratory tests of blood antibodies against polio viruses. But do the oral vaccines really give such a high proportional protection against paralysis? And are they safe? On these questions the scientists divided down the middle.

For the purists, Johns Hopkins University's Dr. David Bodian said that there should be a clear showing, as in the Salk 1954 field trial, based on different paralysis rates among vaccinated and unvaccinated. This was exasperating to both the University of Cincinnati's Dr. Albert B. Sabin and Lederle Laboratories' Dr. Herald R. Cox, developers of two of three U.S. live vaccines. It is an impossible requirement, snapped Dr. Sabin, because by its very nature the oral, weakened virus is designed to multiply in the human digestive tract. It is bound to spread to unvaccinated contacts (especially close kin) of vaccinated subjects, and make some of them immune. So if the vaccine is effective, it will destroy the basis for such a comparison by protecting some of the unvaccinated.

Man & Monkey. Both Sabin and Cox asserted that there is enough evidence from millions of oral vaccinations in a score of foreign countries to show that their vaccines are safe and sure.* But each insisted that his own was better than either of its two rivals. (Dr. Sabin has attacked the third vaccine, developed by the Wistar Institute's Dr. Hilary Koprowski, charging that it contains viruses that cause disease in monkeys and might be dangerous for man.) Dr. Sabin gives his vaccine in three separate doses a month apart--one for each main type of polio virus. Dr. Cox and colleagues give a single swig of trivalent vaccine.

Dr. Cox disclosed that Lederle has already applied to the P.H.S.'s Division of Biologies Standards for a license to make generally available his one-swallow vaccine, now under extensive trial in Miami (TIME, Feb. 29) and Minnesota. Even this brought a demurral. Said Biologies Standards' Dr. Roderick Murray: "No company has yet filed a complete application with all the required data." What he meant was that the Government, once burned when hasty licensing of Salk vaccine producers was followed by the disastrous Cutter incident (TIME, May 9 1955 et seq.}, is now twice shy about licensing an oral vaccine. Main concern is that the weakened viruses sometimes revert, in the human stomach and intestines, to a form that is more likely to cause paralysis in test monkeys. Baylor University's Dr. Joseph L. Melnick settled a years-long argument with conclusive proof of this. But nobody knows whether the monkey test (involving direct injection into the brain or spinal fluid) is a good indicator of what might happen in man.

Toward the Ideal. Many of the recorded failures of Salk vaccination (17% of paralysis victims last year had had three or more shots) were explained by Vaccinventor Jonas E. Salk himself. The commercial vaccine, he declared unequivocally, is only 50% effective (on the average) after a single shot. By simple arithmetic, he argued that two shots would be 75% effective, and three shots, 87.5%. Dr. Salk contrasted this with the efficacy of the hand-tooled vaccine made with craftsman care in his University of Pittsburgh laboratories: 90% effective after one shot, 99% after two, and 99.9% after three. Commercial vaccine, he said, can be brought up to this high standard.

Dr. Maurice R. Hilleman reported that his company (Merck Sharp & Dohme) just happens to have an improved vaccine handy--not yet as potent as Dr. Salk's ideal, but far better than the commercial average: 91% of vaccinated children were protected by only two shots, a month apart, said Dr. Hilleman. Merck has a licensing application on file in Washington, and wants Government action on it before this year's polio season advances.

The live-virus men were sure that they had the only means of wiping out both polio and the viruses that cause it. Dr. Salk was sure that killed vaccines have a great future, against many viral diseases besides polio, and can be raised to one-shot effectiveness. After listening to all the arguments, Dr. Cox grumbled with some justification: "The only things you can be sure of are death, taxes and criticism." Said Dr. Bodian: "Maybe we have too many vaccines against polio."

-- Biggest consumer of an oral vaccine, mad locally to Sabin specifications, is the U.S.S.R. where 50 million people aged 2 to 20 have already had it, and 30 million more are scheduled to get it this year.

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