The elimination of polio in the Scandinavian countries

The Nordic countries, i.e., Denmark, Finland, Iceland, Norway, and Sweden, together with Holland, have all continued to use the killed poliovaccine introduced in the middle of the 1950s and they still use it today. In Denmark, combined vaccination has been practised since 1966, starting with three doses of the killed vaccine and continuing with the oral vaccine. Norway used oral vaccine alone during the 14-year period from 1965 to 1979. In all these countries, the immunizations with the killed vaccine were immediately successful. Poliomyelitis was practically eliminated already by the beginning of the 1960s. After this initial successful period, the different countries experienced different events, from which valuable conclusions can be drawn: 1. Nationwide vaccination with killed vaccine was highly effective. 2. It is of the utmost importance that the potency of the killed vaccine is high. 3. Oral vaccine may cause higher rates of vaccine-associated secondary cases than have been reported in general. 4. In the Nordic countries, the general circulation of wild virus appeared to cease simultaneously with the disease. 5. When virus is reintroduced into the country, unvaccinated groups are vulnerable. Outbreaks in unvaccinated "pockets" have occurred. This phenomenon, however, has also been experienced in countries using oral vaccine. 6. In Stockholm, both wild poliovirus and vaccine-like polio strains were isolated from the sewage water, indicating a constant import of both types of viruses. Virus isolation from thousands of patients with meningitis or diarrhoea have been negative throughout the years.