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Human monkeypox: secondary attack rates
Abstract:
Data on human monkeypox collected in Zaire during the six years 1981-86 were analysed to assess the extent of interhuman transmission of monkeypox virus. Among the 2278 persons who had close contact with 245 monkeypox patients infected from an animal source, 93 fell ill and were presumed to have been infected from the known human source: 69 of these were spread in the first generation, 19 in the second generation, and the remaining five cases in the third and fourth generation.The secondary attack rates were correlated with the age, sex, place of residence, and vaccination status of the contacts. There was an overall 3% probability of becoming ill following infection from a known human source. The affected household was the main focal point for interhuman transmission of monkeypox virus. The highest attack rate (11.7%) occurred among unvaccinated household contacts in the age group 0-4 years. However, the majority of susceptible persons who had been close to patients in the confined space of poorly ventilated huts failed to develop illness. There was no evidence of an increase in the secondary attack rate between 1970-80 and 1981-86.The inefficient spread from person to person, even in conditions of maximum exposure, supports the concept that monkeypox virus is poorly adapted for sustained transmission between humans and that such transmission does not pose a significant health problem.
Insights
Human monkeypox virus shows inefficient person-to-person spread, with a low overall probability of illness following human exposure. Household transmission is most common, particularly in unvaccinated children, but sustained human transmission is unlikely.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- Human monkeypox is a zoonotic disease with potential for limited human-to-human transmission.
- Understanding transmission dynamics is crucial for public health preparedness and response.
Purpose of the Study:
- To analyze human-to-human transmission patterns of monkeypox virus in Zaire.
- To assess factors influencing secondary attack rates in close contacts of infected individuals.
Main Methods:
- Retrospective analysis of monkeypox cases and contacts from 1981-1986 in Zaire.
- Calculation of secondary attack rates based on generation of spread and contact characteristics.
Main Results:
- Among 2278 close contacts of 245 monkeypox patients, 93 secondary cases were identified.
- Overall secondary attack rate was 3%, with highest rates in unvaccinated children (11.7%) within households.
- Inefficient transmission observed even in high-exposure settings, with no increase in rates over time.
Conclusions:
- Monkeypox virus demonstrates poor adaptation for sustained human-to-human transmission.
- Interhuman spread is limited and does not represent a significant public health threat.
- Household contact and vaccination status are key factors in transmission risk.