The Dangerous Short Cut

The Salk vaccine of 1954 was safe, as was proved by more than 400,000 inoculations with only 71 subsequent cases of paralytic polio (none of them attributable to the vaccine). But the Salk vaccine of 1955 is not the same as that of 1954. A big difference is in the testing procedures.

How the Tests Work. On the face of it, nothing could be more thorough than the inactivation and testing procedures worked out by Dr. Jonas E. Salk and adopted as standard by the Public Health Service. To "kill" or (more precisely) inactivate the virus, a formaldehyde solution is added to it. Typically, one cubic centimeter of this is enough to kill the virus in 4,000 cc. of culture. After about , three days only one particle out of 10 million will be left active. In an effort to eliminate even this last particle, the process is continued for as long as 14 days.

Then comes the testing. From every 1,000 cc. of vaccine, one cc. is taken.

Each of these samples is put in a test tube with a tissue culture made from monkeys' kidneys. If there is still any active virus present, it will multiply and, in the process, destroy some of the kidney tissue cells. After a week, technicians use microscopes to see whether kidney cells have in fact been destroyed. If any have, the vaccine batch is thrown out.

But even if no signs of virus can be seen, some of the same vaccine material is tested again, over another week, with fresh kidney tissue. Half a dozen cynom-olgus monkeys get shots (in the arms) ten times as potent as a human child receives. And twelve rhesus monkeys are injected, with the vaccine going into the nervous system--some directly into the brain itself. Even if these monkeys fail to get sick, they must be killed (painlessly by ether) after a month and their nerve tissues are examined minutely.

Last year's vaccine was triple-tested* in the manufacturer's own labs, Dr. Salk's labs at the University of Pittsburgh, and the U.S. Laboratory of Biologies Control.

This year, in an attempt to "short-cut a little bit" (as President Eisenhower put it), the tests were run only by the manufacturers, with the U.S. making an occasional spot check but generally relying on manufacturers' reports. Moreover, last year's vaccine was produced in small lots, like hand-built racing cars, as contrasted with this year's assembly-line production.

Is the Needle to Blame? It now appears that a vaccine can pass rigorous tests and still not be safe for human beings; it seems possible that the arm muscle of the young human animal is the most sensitive of all testing materials for polio virus. It looks as though a vaccine containing only a few stray particles of active virus--which might do no harm to a monkey or great ape when injected into the brain or spinal cord--may touch off paralytic disease when injected into a child's arm.

One explanation is that jabbing a hypodermic into the muscle means cutting or tearing a number of nerves which then offer the virus particles a direct pathway to the brain or spine. This seems plausible because inoculations against other diseases, e.g., diphtheria, may trigger a polio infection even when no polio virus is introduced and the only common factor is the use of the needle.

Is the Strain to Blame? Another explanation has to do with the variable nature of polio strains. Some are virtually incapable of causing paralysis when injected into limb muscles, but readily cause it if they reach the brain. Others are the exact opposite. One of those that most often and consistently cause paralysis when injected into a limb is the Mahoney strain, one of the dozens of strains grouped together in Type I. Why, then, did Dr. Salk pick Mahoney as the Type I strain to be included in his vaccine? For two reasons, he answers: 1) it is a stable and consistent performer that behaves well in the laboratory and can be counted on to give a high antibody response after injection, and 2) it is so effectively killed by the formaldehyde that it is no longer dangerous in his vaccine.

However, there is an increasing suspicion among virologists that the formaldehyde bath does not kill every last virus particle. It does no good to increase the strength of the formaldehyde solution. If that is done, the virus is not merely inactivated but so macerated that the human system no longer recognizes it as virus and will not develop antibodies against it. As for the time the virus is exposed to the formaldehyde, that already runs longer than is theoretically needed to do the job, and may run five times as long. This, Dr. Salk argues, is a safety factor of five.

But in immunology, say Salk's critics, five is little better than no factor at all; they will be satisfied with nothing less than either a vaccine which contains no virus of a strain that can cause paralysis, or safety factors of 100 or more.

* Although the 1954 vaccine was safe, some of it gave little or no protection. Merthiolate, added as a preservative, destroyed its effectiveness. Result: 170,000 youngsters got shots rated as poor or as low moderate; 100,000, moderate, and only 135,000, good.

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