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Modeling the protective effect of previous compulsory smallpox vaccination against human monkeypox infection: from
Tibor Spath1, Sophie Brunner-Ziegler2, Tanja Stamm3
1Medical University of Vienna, Department of Hospital Epidemiology and Infection Control, Vienna, Austria.
Objectives:
Human monkeypox (MPX) cases are escalating worldwide. Smallpox vaccination, which was compulsory in Austria until 1981, was reported to confer 85% cross-protection against MPX.
Methods:
To assess the impact of smallpox vaccine-induced protection, the age-dependent vaccine-induced immunity against human MPX and the probability of infection according to age in the general population of Vienna, Austria, were determined using a modified susceptible-infected-removed model.
Results:
Within the population born before 1981, the average vaccine-induced protective effect was calculated at 50.4%, whereas in the population born thereafter, protection was lacking. The overall probability of infection after exposure to an infected patient was calculated at 73.8%, which exceeds the threshold value of 46.9% for an index patient to infect at least one other person (R ≥1.0).
Conclusion:
Our model shows that if no additional interventions are taken, the collective immunization status of the population alone will not suffice to contain human MPX. Although the majority of cases have occurred in a subpopulation, given the steadily increasing incidence, dissemination into the general population remains possible, as observed before with HIV. Our model emphasizes the need for adequate containment measures and may aid in specific risk assessment because it can easily be adapted to other populations and cohorts worldwide.
Insights
Smallpox vaccination offers limited protection against monkeypox (MPX) in Austria, with only 50.4% efficacy in those vaccinated before 1981. Current vaccination status alone is insufficient to contain MPX outbreaks without additional public health measures.
Area of Science:
- Epidemiology
- Infectious Diseases
- Public Health
Background:
- Human monkeypox (MPX) cases are increasing globally.
- Smallpox vaccination, compulsory in Austria until 1981, provides an estimated 85% cross-protection against MPX.
Purpose of the Study:
- To assess the impact of smallpox vaccine-induced immunity on MPX transmission in Vienna, Austria.
- To determine age-dependent immunity and infection probability in the general population.
Main Methods:
- Utilized a modified susceptible-infected-removed (SIR) model.
- Analyzed age-specific vaccine-induced protection and infection probability.
Main Results:
- Average vaccine-induced protection was 50.4% in individuals born before 1981; no protection was observed in those born after.
- The overall probability of infection post-exposure was 73.8%, exceeding the threshold for sustained transmission (R ≥1.0).
Conclusions:
- Population immunity from smallpox vaccination alone is insufficient to contain MPX.
- Additional containment measures are crucial to prevent widespread dissemination, especially given increasing incidence.
- The model provides a framework for risk assessment adaptable to other populations globally.
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