Design: Systematic review of epidemiological parameters, outbreaks and models
Population: 119 papers covering 23 Nipah outbreaks
Primary outcome: Case fatality, incubation period, seroprevalence, reproduction number
Effect: CFR 9.1% (Singapore) to 81.9% (Bangladesh); median incubation 8.8 days (7.5–10.0)

A systematic review in Lancet Infectious Diseases pulled together 119 papers on Nipah virus, extracting 243 epidemiological parameters, 89 risk factors, 39 models and 23 outbreaks, up to March 2025. It was published on 14 July.

Pooled case fatality varied widely, from 9.1% in Singapore to 81.9% in Bangladesh. Median incubation, from the few studies with usable data, was about 8.8 days (95% CI 7.5–10.0). General-population antibody prevalence ranged from 0% to 12.5%. Four of five central estimates of the reproduction number were below one, meaning most chains of transmission die out. Only eight of 39 mathematical models had been fitted to real data.

For India, where Kerala has had repeated outbreaks, the practical points are the long incubation window for contact follow-up and the consistent pattern of limited onward spread. That makes early isolation and contact tracing effective tools. The variation in fatality likely reflects differences in strain, route of exposure and access to intensive care, but the review cannot separate them. The clinical course remains poorly characterised.

Follow up contacts of a suspected Nipah case for at least the incubation window, around three weeks to cover its range.
Isolate suspected cases early, since most transmission chains are short and early control is effective.
Consider Nipah in encephalitis or severe respiratory illness with exposure in affected districts of Kerala or Bangladesh.
Use full contact and droplet precautions for health workers caring for suspected cases.

Why it matters

It gives outbreak teams the parameters they need, and shows how thin the evidence for many of them still is.

The statistics, in plain English

A reproduction number below one means each case infects, on average, fewer than one other person, so outbreaks tend to burn out. The wide fatality range, with very wide intervals in small outbreaks, reflects few cases rather than a precise difference between countries.