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Poliomyelitis outbreak in South Africa, 1982. II. Laboratory and vaccine aspects
Abstract:
Between May and September 1982 an extensive epidemic of poliomyelitis occurred in Gazankulu in the north-eastern region of South Africa, with a total of 260 paralysed cases and 42 deaths. A three-part study was instituted, the first of which established the aetiological agent of the epidemic to be poliovirus type 1. This was determined initially by serology and later by isolation of the virus, chiefly from stool specimens. The potency of the trivalent oral polio vaccine manufactured at the National Institute for Virology, was evaluated in the second study by in vitro potency testing of samples recalled from the epidemic areas and also in vivo by determining the serological response of seronegative children immunized with fresh vaccine. Nearly half of the vaccine samples withdrawn from the field had sub-optimal titres whereas fresh vaccine produced a very satisfactory serological response. In order to plan immunization rationally, the third study, namely the determination of the immune status of the various populations throughout the country was instituted. This involved both serology, using a neutralization test on randomly collected sera and also an analysis of patient history and health card documentation. With the exception of the urban black area (Soweto), which had high levels of immunity both serologically (75%) and on history, other areas examined had poorer levels of immunity of approximately 52% on serological testing and 57% on history. It is clear that the epidemic was multifactorial in origin, with fall-offs in the level of immunization and evidence of breaks in the cold chain being the major factors.
Insights
A 1982 polio epidemic in South Africa was caused by poliovirus type 1. Sub-optimal vaccine potency and low immunization levels contributed to the outbreak, highlighting the need for improved vaccine management and public health strategies.
Area of Science:
- Epidemiology
- Virology
- Public Health
Background:
- An extensive poliomyelitis epidemic occurred in Gazankulu, South Africa, between May and September 1982, resulting in 260 paralyzed cases and 42 deaths.
- The epidemic prompted a three-part study to identify the cause, evaluate vaccine effectiveness, and assess population immunity.
Purpose of the Study:
- To determine the etiological agent responsible for the 1982 Gazankulu poliomyelitis epidemic.
- To evaluate the potency and effectiveness of the trivalent oral polio vaccine used during the epidemic.
- To assess the immune status of different populations across South Africa to inform future immunization strategies.
Main Methods:
- Virus isolation from stool specimens and serological testing to identify the causative agent.
- In vitro potency testing of recalled vaccine samples and in vivo assessment of serological responses in children.
- Serological neutralization tests on randomly collected sera and analysis of patient history/health card documentation to determine population immunity.
Main Results:
- Poliovirus type 1 was identified as the etiological agent of the epidemic.
- Nearly half of the vaccine samples from the epidemic areas showed sub-optimal potency, while fresh vaccine elicited a satisfactory immune response.
- Immunity levels varied significantly, with Soweto showing high immunity (75% serologically, 57% by history), while other areas had lower immunity (approx. 52% serologically, 57% by history).
Conclusions:
- The poliomyelitis epidemic was multifactorial, with declining immunization levels and compromised vaccine cold chain integrity being major contributing factors.
- The study underscores the critical importance of maintaining optimal vaccine potency and robust immunization programs to prevent polio outbreaks.
- Findings emphasize the need for continued surveillance and strategic planning to ensure adequate population immunity against poliovirus.