Childhood diarrhoea fell by half after Thailand added rotavirus vaccine

Adding rotavirus vaccine to Thailand's national immunisation programme was followed by roughly a halving of childhood diarrhoea, according to a retrospective analysis of national surveillance data [s1]. All-cause acute diarrhoea incidence among children aged 0–59 months fell by 50.0% (incidence rate ratio 0.50; 95% CI 0.39–0.63) and rotavirus-associated incidence by 52.0% (IRR 0.48; 95% CI 0.39–0.59) after the vaccine was introduced in February 2020 [s1].

The finding matters because most of the evidence that rotavirus vaccines work at scale comes from high-income countries; data from low- and middle-income settings, where the disease kills far more children, have been comparatively thin [s1]. WHO recommends rotavirus vaccine in all national immunisation programmes for exactly the populations where diarrhoeal disease is heaviest [s2].

What the study measured

Researchers analysed aggregated national surveillance records (ICD-10-TM codes A00–A09 and K56.1) from Thailand's Health Data Centre, which covers roughly 90% of public health facilities and includes inpatient, outpatient and death records [s1]. Using Poisson regression, they compared a pre-vaccination period (2014–2019) with a post-vaccination period (2021–2024), deliberately excluding 2020 — the introduction year, and the year the COVID-19 pandemic scrambled care-seeking [s1]. Rates were age-stratified, using each birth cohort's differing exposure to the new programme as a proxy for vaccine effect [s1].

Hospitalisations fell further than overall incidence. At one to four years after introduction, admissions for all-cause diarrhoea dropped 58.2% (IRR 0.42; 95% CI 0.30–0.58) and for rotavirus-associated diarrhoea 49.0% (IRR 0.51; 95% CI 0.30–0.88) [s1]. The seasonal pattern also flattened: the pronounced December-to-February peaks that characterise rotavirus transmission became less marked after the vaccine arrived [s1].

What it does not show

Two null results are as informative as the headline declines. All-cause diarrhoea mortality did not change significantly between the pre- and post-vaccination periods (IRR 0.94; 95% CI 0.50–1.77), and rotavirus-specific deaths were too few to analyse — a reminder that in a middle-income country with reasonable hospital care, deaths from diarrhoea are already uncommon, so a vaccine's largest visible payoff is in illness and admissions rather than in a measurable mortality signal [s1].

The second null concerns safety. Earlier rotavirus vaccines were withdrawn decades ago over a small risk of intussusception, a serious bowel obstruction, and the question has shadowed the vaccine class since. In this dataset, intussusception rates among infants aged 0–11 months stayed stable across the post-vaccination period (IRR 1.03; 95% CI 0.82–1.29) [s1].

The design has real limits, and the authors are candid about them. This is an ecological, before-and-after comparison of aggregated national counts, not a trial: individual-level data on who was vaccinated were not available, so the analysis cannot rule out other changes over the decade — in sanitation, care-seeking or coding — that moved diarrhoea rates alongside the vaccine [s1]. The exclusion of 2020 limits but does not erase the pandemic's distorting effect on the surrounding years. What the study offers is a population-level signal consistent in direction and size with the vaccine's expected effect, across incidence, hospitalisation and seasonality at once.

Where it fits

The result lands on the reassuring side of a genuine question about rotavirus vaccines in Asia, where oral vaccines have sometimes performed less well than in high-income settings. A roughly 50% fall in diarrhoea incidence and a 58% fall in admissions, with no intussusception signal, is the kind of real-world evidence that strengthens the case for sustaining the programme — and the authors' own conclusion is blunt: keeping coverage high is what determines how much benefit a country actually banks [s1].

That caveat is the live one. Rotavirus vaccine is only as useful as the share of infants who receive it on time, which ties this story to the broader picture of stalling childhood immunisation coverage and to the gaps mapped in the latest vaccination estimates. For Thailand, the data say the vaccine did what it was meant to; whether that holds depends on the duller work of getting doses into children year after year.

Sources

• Incidence of acute diarrhoea among children (0-59 months old) in Thailand after introduction of rotavirus vaccine: a retrospective national database analysis (2014-2024) — The Lancet Regional Health - Southeast Asia, 3 June 2026
• Rotavirus (immunization and disease context) — World Health Organization