Transmission dynamics of Nipah virus in Bangladesh and India, 2001–2026: systematic review and inference on reproduction number, offspring dispersion, and serial interval

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Abstract Background Nipah virus (NiV) is a priority zoonotic pathogen causing high-fatality outbreaks. Early NiV outbreaks in Malaysia and Singapore had limited transmission beyond spillover events. However, since 2001, NiV outbreaks with person-to-person transmission have occurred in Bangladesh and India, driven by the NiV-Bangladesh genotype and NiV-India genotype. Our study aims to estimate the reproduction number, offspring dispersion, and serial interval governing NiV transmission in Bangladesh and India during 2001–2026. Methods We conducted a systematic review of NiV outbreak investigations in Bangladesh and India, searching PubMed, Embase, Web of Science, and grey literature through 28 February 2026. Case-level offspring counts from 27 eligible sources (323 cases across 67 outbreaks) were used as input to a hierarchical Bayesian negative binomial offspring distribution model. The serial interval was estimated by parametric distribution fitting to 137 transmission pairs. Country-stratified and sensitivity analyses were performed to evaluate the robustness of estimates. Results Pooling across 67 outbreaks, we estimated a median reproduction number of 0.46 (95% CrI: 0.28–0.73), an offspring dispersion parameter of 0.07 (0.05–0.10), and a serial interval of 13.3 days (95% CI: 12.8–13.8). Country-stratified median reproduction numbers were 0.48 (0.23–0.97) for India and 0.35 (0.19–0.59) for Bangladesh, and dispersion parameters were 0.04 (0.02–0.07) and 0.11 (0.06–0.18), respectively, indicating marked overdispersion in both settings. Conclusion NiV transmission is self-limiting on average and highly overdispersed, suggesting that a disproportionate share of onward transmission arises from a small number of cases. This epidemiological profile supports targeted containment measures, including contact tracing and quarantine, for effective NiV outbreak control. Author Summary Nipah virus is a deadly infection that spreads from bats to people and, in some cases, from one person to another. Despite its fatality, there is no licensed vaccine or specific treatment. Since 2001, outbreaks have occurred almost every year in Bangladesh and India, which are the only places where person-to-person transmission can be studied directly. We gathered case reports from these outbreaks over twenty-five years and used a statistical model to measure how the virus spread between people. We found that, on average, each infected person passes the virus to fewer than one other person, so outbreaks tend to die out on their own without repeated introductions from animals. However, spread is very uneven: most people infect no one, while a small number infect many, occasionally producing large clusters, often in hospitals and among caregivers. We also measured the typical time between one person falling ill and the next (serial interval), about thirteen days. Together, these findings provide a better understanding of the Nipah virus transmission and updated numbers needed to plan future prevention and control strategies of Nipah outbreaks.

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