The Choice Between Killed- and Live-Virus Poliomyelitis Immunization

Abstract

FEW subjects in the field of infectious disease have evoked as much in the way of controversy and confusion as vaccination against poliomyelitis. Each of the two types of vaccinekilled-virus and live-virus-has its opinionated proponents, and the recent publicly expressed doubts concerning the safety of attenuated poliovirus 1 are likely to increase the uncertainty of the physician regarding what course to follow in the practice of anti-polio immunization. The object of this article is to present a survey of the subject so that an informed choice can be made by the reader. Immunization with Inactivated PoliovirusFormalin-killed-virus poliovaccine of the Salk type has been in use for nine years, and an accurate assessment of its value can be made.Manufacturing requirements were made more stringent after the Cutter incident of 1955, and there is no reason to question its present safety. As measured by prevention of paralytic poliomyelitis its effectiveness is 60 to 80 per' cent after two doses, 80 to 90 per cent after three doses and 85 to 95 per cent after four doses .2, ' These variations in effectiveness reflect the potency of the preparations of vaccine used and the type of poliovirus causing the paralysis. Studies of persistence of antibody after primary vaccination and boosters with commercially available vaccine have shown that at least one type of antibody disappears in one-quarter to two-thirds of infants by a year after the last inoculation.4.;¡ ~' Salk 3 has suggested that individuals who lack antibody after killed-virus vaccination may still be immunologically sensitized, but this supposition is unproven. Thus, if the presence of antibody is deemed necessary as evidence of immunity, the prospect is that revaccination should be practiced annually or biennially.'T he serologic response to Salk vaccine has been poor in infants below the age of three months, owing to the presence of maternal antibody and the relatively immature immunologic mechanisms.,, 8.!) ° Vaccination in infancy should begin with three inoculations at one-monthly intervals, followed by a booster some six months later. At other ages, two primary inoculations should be followed by a booster seven to 12 months later.