Surveillance of the Safety of Oral Poliomyelitis Vaccine in England and Wales 1962-4.

When, in 1956, inactivated poliomyelitis (Salk) vaccine became available for routine immunization in England and Wales the Ministry of Health set up a scheme of poliomyelitis surveillance. The objects were to provide a means of rapid detection pf possible outbreaks of vaccine-induced poliomyelitis, such as occurred in the United States owing to the presence of incompletely inactivated virus in a batch of vaccine (Nathanson and Langmuir, 1963), and to observe the efficacy of the vaccine. The results were reported by Geffen and Spicer (1960), Geffen (1960), and Roden (1964), and though a number of vaccineassociated cases occurred they concluded that the vaccine was both safe and effective. After live attenuated (Sabin) vaccine was introduced in 1962 the surveillance scheme was reorganized by the Ministry of Health and the Public Health Laboratory Service with the new aim of meeting the theoretical objection that disease might be caused in a very small proportion of persons receiving the vaccine, or their contacts, owing to the virus regaining some of its neurovirulence on passage through the human alimentary tract, a risk which would be detectable only when very large numbers of persons had been immunized. The scheme depended on inquiry into notified cases of poliomyelitis, and also on spec al studies of notified encephalitis and cases in which poliovirus isolation was reported. In assessing the safety of oral vaccine the following circumstances were regarded as significant indicators of possible vaccine-induced disease: (1 undue frequency of poliomyelitis in recently vaccinated persons ; (2) an aggregation of dates of onset of illness within a month of vaccination, particularly between 5 and 28 days; (3) undue frequency of cases associated with a single batch, or small number of batches of vaccine; and (4) an age, sex, seasonal, and geographical distribution of vaccine-associated cases inconsistent with the distribution of other cases of poliomyelitis. Galbraith (1963) analysed the results for 1962 and concluded there was no evidence of vaccine-induced disease at that time, although studies in the United States (Terry, 1962) suggested that a few cases of paralytic poliomyelitis in vaccinated persons might have been caused by the vaccine and that the risk, though small, was greatest after administration of type 3 monotypic vaccine to adults. These findings have been endorsed by a more recent review of cases in the United States (Special Advisory Committee, 1964). The present paper summarizes the results of surveillance in England and Wales for the three years 1962-4, during which oral vaccine has been used for routine immunization.