Study identification

EU PAS number

EUPAS1000000813

Study ID

1000000813

Official title and acronym

DARWIN EU® - Encephalitis risk in pediatric varicella vaccine recipients

DARWIN EU® study

Yes

Study countries

Denmark
Finland
Norway
Spain

Study description

Varilrix and Varivax are authorised for the prevention of varicella infection (chickenpox) in adults, children, and adolescents aged 9–12 months of age and older. Both vaccines contain the live-attenuated varicella virus (OKA strain). In June 2025, the EMA Pharmacovigilance Risk Assessment Committee (PRAC) reviewed the risk of encephalitis associated with these vaccines, following a report of a fatal case in a paediatric recipient of Varilrix. Varicella vaccines are widely used across the EU, and encephalitis is listed as an adverse reaction in their product information, based on rare reports during post-marketing surveillance, however, observational evidence is scarce.
Cases of encephalitis with fatal outcome are extremely rare given the extensive use of varicella vaccines. Data from US spontaneous reports showed <1 case per million doses administered. Encephalitis is also a recognised but rare complication following severe varicella infection itself, in about 1–2 cases per 10,000 infected children and adolescents, with a higher risk in immunocompromised individuals. Considering the seriousness of encephalitis and the regulatory context, further investigation is needed.

Study status

Ongoing
Research institutions and networks

Institutions

Networks

Contact details

Xintong Li

Primary lead investigator

Study timelines

Date when funding contract was signed

Planned:

Study start date

Planned:
Actual:

Date of final study report

Planned:
Sources of funding
EMA
Regulatory

Was the study required by a regulatory body?

Yes

Is the study required by a Risk Management Plan (RMP)?

Not applicable