Rapid modelling of the 2026 Andes virus outbreak predicts limited transmissibility and low mainland outbreak risk

In May 2026, an outbreak of Andes virus infection was reported among passengers and crew of the cruise ship MV Hondius. As of 27 May, 13 linked cases and three deaths have been reported, with ongoing concerns about the potential for onward transmission outside of the cruise ship following disembarkation. Here, we provide a responsive analysis of the ongoing outbreak, using publicly available data and a stochastic agent-based model of onboard transmission to estimate the probability of transmission per close contact.  Our model identified a pattern of superspreading driving the course of the infection onboard the ship. After accounting for this early heterogeneity, the model estimated per-contact transmissibility was low, with a median value of 0.006 (95% interval: 0.001, 0.019). This corresponds to an onboard R₀, describing the expected number of infections driven by an average infected person on the ship, of 0.36 (95% interval: 0.11, 1.24).  Extrapolating this result to contact rates typical of the mainland UK, we estimated a mainland R₀ of 0.19 (95% interval: 0.06, 0.67), below the R = 1 threshold required for sustained transmission.  Continued control measures remain appropriate given the severity of ANDV infection, and our result does not exclude the possibility of onward viral transmission if containment measures were to fail.  Nevertheless, our findings predict that the overall risk of a sustained or sizeable mainland outbreak from ANDV 2026 is low.