Safety v. Potency

As the season of epidemic polio moved northward, the quality and effectiveness of U.S. polio vaccine were being debated last week on both sides of the Atlantic. In Britain, despite a shortage of home-brewed vaccine, Health Minister Dennis Vosper took a harsh jab at the American product by announcing that he had "accepted expert medical advice that Britain should not run the risk of importing poliomyelitis vaccine." Snorted the British Medical Journal: "It is difficult to believe . . . that the safety of poliomyelitis vaccine as used now in the U.S.A. is seriously questioned. If its antigenic potency [ability to stimulate production of protective antibodies] is in doubt, some doctors might well like to give their patients the benefit of this doubt."

In fact, though some U.S. experts were still exercised about highly technical problems involved in guaranteeing the vaccine's safety, the public apparently had little cause for worry on this score. Since the flurry of vaccine-precipitated cases at the time of the Cutter incident (TIME, May 9, 1955 et seq.), safety-testing procedures have been made more stringent, and there have been no more such cases.

More nagging and worrisome today than doubts about safety is concern over the less dramatic question of potency. The National Institutes of Health rules require manufacturers to use a certain amount of formaldehyde to kill the virus. The trick is to use just enough to destroy the virus' ability to cause infection, but leave a well-preserved virus corpse that can still stimulate the inoculated subject's system to produce antibodies.

Before vaccine can go to market, potency is tested in chickens and monkeys. The manufacturer must test every batch; N.I.H. spot-checks a batch here and there. How tricky it is to combine potency with safety was shown last month when Indianapolis' Eli Lilly & Co., after successfully producing 109 million shots (two-thirds of all used in the U.S.), had to withhold 6,000,000 shots from the market because they flunked their potency tests. Retesting will take another month.

In an effort both to reduce the amount of formaldehyde needed and to insure a thoroughly killed but still potent vaccine, Detroit's Parke, Davis & Co. has added another step: centrifuging the virus (after formaldehyde treatment) and making a thin film which is irradiated with ultraviolet light. The company has produced 25.5 million shots this way, is the only producer using the method (developed in cooperation with Chicago's Michael Reese Research Foundation and General Motors' research laboratories) for U.S. sale; Wyeth Laboratories uses it for export vaccine.

Parke, Davis reports no potency problems. Partisans of what has come to be known as the Reese method of ultraviolet inactivation contend that it definitely produces a superior vaccine. Of this there is no proof. But there is reason to fear that some vaccine already used may have been no more potent than colored water in conferring protection against paralytic polio. A further unanswered question is the effect of storage on potency. Manufacturers may store vaccine under refrigeration for six months after potency testing; once it is released from their coolers, it must be used within six months. All vaccine deteriorates somewhat with time; a batch that barely scrapes by the potency tests might well be worthless before its expiration date. The N.I.H. frankly admits that it has no data on this.

With the possibility that some, even many, shots are being given with inert material, there arises the danger that the U.S. public is being lulled into a false sense of security about polio. While Vaccinventor Jonas Salk is suggesting that the present three-shot course of inoculations could be cut to two, more conservative polio experts are arguing that more shots, not fewer, are needed. Not enough time has elapsed, and not enough children inoculated with commercial vaccine have been tested, to show whether antibody levels high enough to give immunity are maintained for more than a year or two. The recommended answer: a booster shot every year. By the law of averages, this would also minimize the chance that any individual might receive successive doses of safe but impotent vaccine.

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