Data-driven estimation of the instantaneous reproduction number and growth rates for the 2022 monkeypox outbreak in Europe

Objective: To estimate the instantaneous reproduction number Rt and the epidemic growth rates for the 2022 monkeypox outbreaks in the European region. Methods: We gathered daily laboratory-confirmed monkeypox cases in the most affected European countries from the beginning of the outbreak to September 23, 2022. A data-driven estimation of the instantaneous reproduction number is obtained using a novel filtering type Bayesian inference. A phenomenological growth model coupled with a Bayesian sequential approach to update forecasts over time is used to obtain time-dependent growth rates in several countries. Results: The instantaneous reproduction number Rt for the laboratory-confirmed MPX cases in Spain, France, Germany, the UK, the Netherlands, Portugal, and Italy. At the early phase of the outbreak, our estimation for Rt, which can be used as a proxy for the basic reproduction number R0, was 2.32 (95% CI 1.81-3.05) for Spain, 2.91 (95% CI 2.33-3.52) for France, 1.84 (95% CI 1.55-2.31) for UK, 3.16 (95% CI 2.55-3.64) for Germany, 2.97 (95% CI 2.01-4.32) for the Netherlands, 1.18 (95% CI 0.98-1.33) for Portugal, 3.74 (95% CI 2.91-4.49) for Italy. Cumulative cases for these countries present subexponential rather than exponential growth dynamics. Conclusions: Our findings suggest that the current monkeypox outbreaks present limited transmission chains of human-to-human secondary infection so the possibility of a huge pandemic is very low. Confirmed monkeypox cases are decreasing significantly in the European region, the decline might be attributed to public health interventions and behavioral changes in the population due to increased risk perception. Nevertheless, further strategies toward elimination are essential to avoid the subsequent evolution of the monkeypox virus that can result in new outbreaks.