Varicella

水痘

Evidence-backed information EN 6/7 applicable sections · ZH 6/7 applicable sections Updated Oct 23, 2026

Varicella (chickenpox) is a highly contagious disease caused by the varicella-zoster virus (VZV), a member of the herpesvirus family for which humans are the only known natural hosts ^[1]. The virus is found worldwide, and primary infection results in chickenpox; after recovery, the virus becomes inactive in nerve cells and can reactivate later as shingles (herpes zoster) ^[1]^[2]. The disease tends to occur more often during winter and spring or cool and dry months, with outbreaks occurring every 2–5 years ^[1]. While typically mild in children, varicella can be more severe in adolescents and adults ^[1]^[2].

Read the full clinical and epidemiological profile 7

Definition

Varicella, commonly known as chickenpox, is a febrile vesicular rash disease caused by primary infection with the varicella-zoster virus (VZV), also called human herpesvirus 3 ^[1]^[2]. After primary infection, VZV establishes latency in peripheral ganglia, and reactivation decades later causes herpes zoster (shingles) ^[3]. VZV is the only human herpesvirus for which highly effective vaccines are available ^[2].

Clinical features

Primary varicella presents as a febrile illness with a characteristic vesicular rash that progresses from macules to papules, vesicles, pustules, and crusts ^[2]. The disease can be more severe in immunocompromised individuals, infants, and adults ^[2]^[3]. Complications may include secondary bacterial infection of skin lesions, pneumonia, and encephalitis ^[2]. Following primary infection, VZV establishes latency in ganglionic neurons; reactivation can lead to postherpetic neuralgia and other neurological syndromes ^[2]^[3].

Epidemiology

VZV is found worldwide, with chickenpox occurring more frequently during winter and spring or cool and dry months ^[1]. Epidemics typically occur every 2–5 years ^[1]. The disease is generally mild in children but tends to be more severe in adolescents and adults ^[1].

Transmission

The virus spreads through respiratory droplets when someone with chickenpox coughs or sneezes, releasing infected droplets into the air, and through direct contact with fluid from the chickenpox blisters ^[1]. Susceptible individuals—those who have not had chickenpox or been vaccinated—are highly likely to contract the virus upon exposure ^[1].

Prevention

VZV is the only human herpesvirus for which highly effective vaccines are available ^[2]. A live attenuated varicella vaccine is used to prevent chickenpox, primarily in children ^[2]^[3]. Vaccination establishes latency similar to wild-type infection, and long-term immunity to varicella develops after either natural infection or vaccination ^[2]. However, immunity from vaccination or prior infection does not protect against reactivation leading to shingles ^[2].

Surveillance note

GlobalID source-data note: Ireland and Japan publish varicella series restricted to hospitalised cases, while other countries report broader notification or sentinel series. Hospitalised-case counts measure a severe subset and should not be interpreted as all community varicella or compared directly with unrestricted series.

References

1 World Health Organization. Chickenpox [Internet]. cited 2 Sept 2026. Available from: https://www.who.int/news-room/questions-and-answers/item/chickenpox
2 Gershon AA et al. Varicella zoster virus infection. Nat Rev Dis Primers. 2015 Jul 2. PMID: 27188665. doi: 10.1038/nrdp.2015.16. PubMed: https://pubmed.ncbi.nlm.nih.gov/27188665/
3 Kennedy PGE et al. Clinical Features of Varicella-Zoster Virus Infection. Viruses. 2018 Nov 2. PMID: 30400213. doi: 10.3390/v10110609. PubMed: https://pubmed.ncbi.nlm.nih.gov/30400213/
4 Patil A et al. Herpes zoster: A Review of Clinical Manifestations and Management. Viruses. 2022 Jan 19. PMID: 35215786. doi: 10.3390/v14020192. PubMed: https://pubmed.ncbi.nlm.nih.gov/35215786/