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Varicella Vaccine Effectiveness During Day-Care Outbreaks: A Comparative Study

Article For Year 2 Vaccination 6 min read

Authored by GSK Vaxipedia

In this article

Summary

Key points

Varicella demonstrates high transmissibility, with secondary attack rates of 61–100% (CI not reported), driving frequent outbreaks in day-care settings^1,5
Breakthrough varicella cases occur post-vaccination, but are typically milder with fewer lesions and lower complication risk¹¹
Overall vaccine effectiveness during outbreaks is ~71% (95% CI: 57–81), with higher protection against moderate disease ~89% (95% CI: 78–95)¹
Single-dose varicella vaccination provides limited protection ~62% VE (95% CI: 43–75) and is insufficient for outbreak prevention in high-exposure settings¹
Two-dose vaccination significantly improves protection, achieving ~94% (95% CI: 75–98) vaccine effectiveness against varicella¹
Two-dose schedules demonstrate ~91–92% (range across studies; CI not reported) effectiveness with no evidence of waning protection over time⁹
Higher effectiveness is observed against moderate-to-severe disease, indicating strong protection against clinically significant illness¹
Two-dose varicella vaccination enhances outbreak control, reduces transmission, and supports herd immunity in closed settings⁹

Introduction

Chickenpox, caused by the varicella-zoster virus (VZV), is a highly contagious infection and a common childhood disease. In non-vaccinated populations, the annual incidence ranges from 13–16 cases per 1000 individuals, with a lifetime risk exceeding 95%. Although often considered a mild illness, varicella can lead to serious complications. The virus spreads easily through close contact, with high secondary attack rates among susceptible individuals.^{1, 2}

Infected persons are typically contagious 1–2 days before the rash appears and remain infectious until all lesions have crusted. The disease is characterized by an itchy, vesicular rash and systemic symptoms, and the illness usually lasts 4–7 days, often resulting in 5–6 days of missed school or childcare among affected children.²

Because of its high transmissibility, outbreaks frequently occur in day-care centers and schools. Although vaccination has greatly reduced disease burden worldwide, outbreak investigations remain important for evaluating real-world vaccine effectiveness in high-contact settings.^3,4

Varicella Transmission in Day-Care Settings

Children attending day-care centers experience frequent close contact, facilitating rapid spread of VZV. Prior to the availability of vaccination, secondary attack rates in susceptible individuals exposed to varicella ranged from 61% to 100%, highlighting the high transmissibility of the virus.^1,5
Even after vaccine introduction, outbreaks may occur in settings with incomplete vaccine coverage or where a large proportion of children have received only a single dose.⁶

Outbreak investigations therefore play an essential role in assessing how well vaccination protects children under conditions of intense exposure.

Recommended Vaccination Schedule

The most effective way to prevent chickenpox is vaccination.² Two doses of the varicella vaccine are recommended for children, adolescents, and adults who have not had chickenpox or have not been previously vaccinated.² The IAP recommended varicella vaccine dosage in India is given below⁷:

Dose	Months
1^st Dose	15
2^nd Dose	18-19

Adapted from Rao MIS, et al. Indian Pediatr. 2024

IAP recommends that the second dose of the varicella vaccine should be administered 3–6 months later, after the 1^st dose.⁷

Overcoming Limitations of One-Dose Vaccination with Two-Dose Varicella Strategies

The one-dose varicella vaccination program has significantly reduced disease incidence and severe outcomes across age groups. However, important limitations remain⁸:

Insufficient population immunity to interrupt transmission
Continued outbreaks in highly vaccinated school settings
Ongoing risk of breakthrough infections, with potential transmission to susceptible high-risk individuals
Associated public health and economic burden due to outbreak control measures

In this context, the World Health Organization recommends a 2-dose schedule of varicella-containing vaccine for effective prevention, given its higher effectiveness compared to a single dose⁹

Two-dose schedule ensures durable protection against varicella⁹
Across studies, two-dose varicella vaccination shows high effectiveness (~91–92%) against varicella of any severity⁹
~67% long-term efficacy (10 years) demonstrated with single-antigen vaccines
Significantly reduces breakthrough infections⁹
No evidence of waning effectiveness with two-dose schedule⁹
Enhances both individual protection and herd immunity, helping limit transmission⁹

Impact of Vaccination on Disease Severity: What Happens in Breakthrough Cases?¹¹

Breakthrough varicella is infection with wild-type varicella-zoster virus (VZV) occurring in a vaccinated person more than 42 days after varicella vaccination.

It is less common in individuals who have received two vaccine doses than in those with only one dose.
Illness is typically milder among two-dose recipients.

Comparative Evidence from Day-Care Outbreak Investigations: Single Dose vs Double Dose¹

In an investigation of seven varicella outbreaks in German day-care centers involving 1084 children, differences in protection were observed according to vaccination status and number of doses. The overall adjusted vaccine effectiveness (VE) against any varicella disease was 71% (95% CI: 57–81), p<0.001.

Protection varied by disease severity, indicating the trend of stronger protection against more severe illness. Importantly, vaccine effectiveness also differed by number of doses. Children who received one dose showed lower VE of 62% whereas those who received two doses had substantially higher protection with 94% VE. These findings highlight that while a single dose provides moderate protection, a two-dose schedule offers significantly stronger protection and may better prevent outbreaks in high-exposure settings such as day-care centers.

Conclusion

Evidence from outbreak investigations in day-care centers highlights the substantial effectiveness of varicella vaccination in preventing infection and reducing disease severity in young children.¹ Although breakthrough infections may occur, particularly after a single vaccine dose, vaccinated individuals generally experience milder illness.¹¹ The adoption of two-dose vaccination strategies further enhances protection and contributes to improved outbreak control in high-contact environments.^1,9 Continued surveillance and outbreak analysis remain important for optimizing vaccination strategies and reducing the burden of varicella in pediatric populations.

Key Safety Information¹²

Contraindications:

Hypersensitivity to any active substance or excipient or neomycin. or varicella vaccine. Primary or acquired immunodeficiency who have total lymphocyte count <1200 per mm3 or other evidence of lack of cellular immune competence or subjects receiving immunosuppressive therapy (including high dose corticosteroids).

Pregnancy:

Avoid pregnancy for 1 month following vaccination.

Special warnings and precautions:

Postpone administration in acute febrile illness. Syncope (fainting) can occur following, or even before any vaccination, with adolescents, as a psychogenic reaction to injection. Avoid all contact with pregnant women susceptible to varicella (especially during first trimester pregnancy) and with high risk for developing severe varicella, especially when person vaccinated develops skin eruption within 2 to 3 weeks of immunization. To reduce infection risk of high-risk subjects, non-immune persons living in close contact with varicella patients or high-risk patients should be vaccinated. A decision should be made either to discontinue breastfeeding or to abstain from vaccination with VARILRIX, taking into account the benefit of breastfeeding for the child with regard to the benefit of prophylaxis against Varicella for the woman.

Undesirable effects: Very common- redness, pain at the injection site.

For the use only of a Registered Medical Practitioner or a Hospital or a Laboratory

References

Spackova M, Wiese-Posselt M, Dehnert M, Matysiak-Klose D, Heininger U, Siedler A. Comparative varicella vaccine effectiveness during outbreaks in day-care centres. Vaccine. 2010;28(3):686-691. doi:10.1016/j.vaccine.2009.10.086
About Chickenpox (Varicella). CDC. Updated April 24, 2024. Accessed April 27, 2026. https://www.cdc.gov/chickenpox/about/index.html
Kendra Viner, Dana Perella, Adriana Lopez, Stephanie Bialek, Claire Newbern, Rodrerica Pierre, Niya Spells, Barbara Watson, Transmission of Varicella Zoster Virus From Individuals With Herpes Zoster or Varicella in School and Day Care Settings, The Journal of Infectious Diseases, Volume 205, Issue 9, 1 May 2012, Pages 1336–1341, https://doi.org/10.1093/infdis/jis207
Miron D, Lavi I, Kitov R, Hendler A. Vaccine effectiveness and severity of varicella among previously vaccinated children during outbreaks in day-care centers with low vaccination coverage. Pediatr Infect Dis J. 2005;24(3):233-236. doi:10.1097/01.inf.0000154323.20387.82
Seward JF, Zhang JX, Maupin TJ, et al. Contagiousness of varicella in vaccinated cases: a household contact study. JAMA. 2004;292:704–708.
Leung J, Lopez AS, Marin M. Changing Epidemiology of Varicella Outbreaks in the United States During the Varicella Vaccination Program, 1995-2019. The Journal of Infectious Diseases. 2022 Oct;226(Suppl 4):S400-S406. DOI: 10.1093/infdis/jiac214. PMID: 36265851; PMCID: PMC10155060.
Rao M IS, Kasi SG, Dhir SK, et al. Indian Academy of Pediatrics (IAP) Advisory Committee on Vaccines and Immunization Practices (ACVIP): Recommended Immunization Schedule (2023) and Update on Immunization for Children Aged 0 Through 18 Years. Indian Pediatr. 2024;61(2):113-125.
Shapiro ED, Marin M. The Effectiveness of Varicella Vaccine: 25 Years of Postlicensure Experience in the United States. J Infect Dis. 2022;226(Suppl 4):S425-S430. doi:10.1093/infdis/jiac299
World Health Organization. WHO position paper on varicella vaccines – November 2025. Wkly Epidemiol Rec. 2025;100(47):567–590 Accessed April 27, 2026
Clinical overview of chickenpox (varicella). CDC. Updated July 15, 2024. Accessed April 27, 2026. https://www.cdc.gov/chickenpox/hcp/clinical-overview/index.html
Clinical features of chickenpox (varicella). CDC.Updated June 5, 2024. Accessed April 27, 2026. https://www.cdc.gov/chickenpox/hcp/clinical-signs/index.html
Varilrix, Abbreviated Prescribing Information, Version: VRX/PI/IN/2024/01 v02 dated. 05 September 2024 https://india-pharma.gsk.com/media/s0ehlauz/varilrix.pdf

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For the use only of a registered medical practitioner or a hospital or a laboratory. Trademarks are owned by or licensed to the GSK group of companies. Refer to full prescribing information before use. Registered medical practitioners can refer company website http://india-pharma.gsk.com/en-in/products/prescribing-information/ for full Product Information. Please report adverse events with any GSK product to the company at [email protected] ©2026 GSK group of companies or its licensor. For more information, please contact: GlaxoSmithKline Pharmaceuticals Limited, Dr. Annie Besant Road, Worli, Mumbai – 400030 (India).

CL Code: PM-IN-VAR-WCNT-260005 | DOP: June 2026

For more information, please refer the following link

https://india-pharma.gsk.com/media/s0ehlauz/varilrix.pdf

For Indian Healthcare Professionals Only

Key Safety Information

Contraindications:

Hypersensitivity to any active substance or excipient or neomycin. or varicella vaccine. Primary or acquired immunodeficiency who have total lymphocyte count <1200 per mm³ or other evidence of lack of cellular immune competence or subjects receiving immunosuppressive therapy (including high dose corticosteroids).

Pregnancy:

Avoid pregnancy for 1 month following vaccination.

Special warnings and precautions:

Undesirable effects: Very common- redness, pain at the injection site.

For the use only of a Registered Medical Practitioner or a Hospital or a Laboratory

Abbreviated Prescribing information of VARILRIX (Varicella Vaccine, Live IP)

ACTIVE INGREDIENT: Each 0.5 ml of the reconstituted vaccine contains: Live attenuated varicella virus (OKA strain, propagated in MRC5 human diploid cells) not less than 10^3.3 plaque-forming units (PFU).

INDICATION: VARILRIX is indicated for active immunisation against varicella of healthy subjects and susceptible healthy close contacts from the age of 12 months onwards. Susceptible healthy close contacts should be immunised in order to reduce the risk of transmission of virus to high-risk patients. These include parents and siblings of high-risk patients, and medical, paramedical personnel and other people who are in close contact with varicella patients or high-risk patients.

POSOLOGY AND ADMINISTRATION: Posology: The immunisation schedules for VARILRIX should be based on official recommendations. Healthy individuals: Children from 12 months of age, adolescents and adults: Children from the age of 12 months as well as adolescents and adults receive two doses of VARILRIX to ensure optimal protection against varicella. The second dose should generally be given at least 6 weeks after the first dose. Under no circumstances should the interval between the doses be less than 4 weeks. Individuals at high risk of severe varicella: Individuals at high risk of severe varicella may benefit from re-vaccination following the 2-dose schedule. Periodic measurement of varicella antibodies after immunisation may be indicated in order to identify those who may benefit from re-immunisation. Under no circumstances should the interval between the doses be less than 4 weeks. Interchangeability: A single dose of VARILRIX may be administered to subjects who have already received a single dose of another varicella-containing vaccine. A single dose of VARILRIX may be administered followed by a single dose of another varicella-containing vaccine. Method of administration: VARILRIX is to be injected subcutaneously (SC) in the deltoid region or in the anterolateral area of the thigh.

CONTRA-INDICATIONS: VARILRIX is contraindicated in individuals with severe humoral or cellular (primary or acquired) immunodeficiency such as: subjects with immunodeficiency states with a total lymphocyte count less than 1,200 per mm³; subjects presenting other evidence of lack of cellular immune competence (e.g. patients with leukaemias, lymphomas, blood dyscrasias, clinically manifest HIV infection); subjects receiving immunosuppressive therapy including high dose of corticosteroids; severe combined immunodeficiency; agammaglobulinemia; AIDS or symptomatic HIV infection or an age-specific CD4+ T-lymphocyte percentage in children below 12 months: CD4+ <25%; children between 12-35 months: CD4+ < 20%; children between 36-59 months: CD4+ < 15%. Hypersensitivity to the active substance or to any of the excipients or to neomycin. However, a history of contact dermatitis to neomycin is not a contraindication. VARILRIX is contraindicated in subjects having shown signs of hypersensitivity after previous administration of varicella vaccine. Pregnancy- Furthermore, pregnancy should be avoided for 1 month following vaccination.

SPECIAL WARNINGS and SPECIAL PRECAUTIONS: As with other vaccines, the administration of VARILRIX should be postponed in subjects suffering from acute severe febrile illness. However, the presence of a minor infection, such as a cold, should not result in the deferral of vaccination.

Syncope (fainting) can occur following, or even before any vaccination especially in adolescents as a psychogenic response to the needle injection. This can be accompanied by several neurological signs such as transient visual disturbances, paraesthesia and tonic-clonic movements during recovery. It is important that procedures are in place to avoid injury from faints. As with all injectable vaccines, appropriate medical treatment and supervision should always be readily available in case of a rare anaphylactic reaction following the administration of the vaccine. Alcohol and other disinfecting agents must be allowed to evaporate from the skin before injection of the vaccine since they can inactivate the attenuated viruses in the vaccine. Limited protection against varicella may be obtained by vaccination up to 72 hours after exposure to natural disease. As with any vaccine, a protective immune response may not be elicited in all vaccinees. As for other varicella vaccines, cases of varicella disease have been shown to occur in persons who have previously received VARILRIX. These breakthrough cases are usually mild, with a fewer number of lesions and less fever as compared to cases in unvaccinated individuals. Transmission: Transmission of the Oka varicella vaccine virus has been shown to occur at a very low rate in seronegative contacts of vaccinees with rash. Transmission of the Oka varicella vaccine virus from a vaccinee who does not develop a rash to seronegative contacts cannot be excluded.

Compared to healthy vaccinees, leukaemia patients are more likely to develop a papulovesicular rash. In these cases too, the course of the disease in the contacts was mild. Vaccine recipients, even those who do not develop a varicella-like rash, should attempt to avoid contact, whenever possible, with high-risk individuals susceptible to varicella for up to 6 weeks following vaccination. In circumstances where contact with high-risk individuals susceptible to varicella is unavoidable, the potential risk of transmission of the varicella vaccine virus should be weighed against the risk of acquiring and transmitting wild-type varicella virus. High-risk individuals susceptible to varicella include: Immunocompromised individuals; Pregnant women without documented positive history of varicella (chickenpox) or laboratory evidence of prior infection; Newborns of mothers without documented positive history of chickenpox or laboratory evidence of prior infection. The mild nature of the rash in the healthy contacts indicates that the virus remains attenuated after passage through human hosts. Individuals at high risk of severe varicella: There is only limited data from clinical trials available for VARILRIX (+4°C formulation) in individuals at high risk of severe varicella.

Vaccination may be considered in patients with selected immune deficiencies where the benefits outweigh the risks (e.g. asymptomatic HIV subjects, IgG subclass deficiencies, congenital neutropenia, chronic granulomatous disease, and complement deficiency diseases). Immunocompromised patients who have no contraindication for this vaccination may not respond as well as immunocompetent subjects, therefore some of these patients may acquire varicella in case of contact, despite appropriate vaccine administration. These patients should be monitored carefully for signs of varicella. Should vaccination be considered in individuals at high risk of severe varicella, it is advised that: maintenance chemotherapy should be withheld one week before and one week after immunisation of patients in the acute phase of leukaemia. Patients under radiotherapy should normally not be vaccinated during the treatment phase. Generally, patients are immunised when they are in complete haematological remission from their disease. The total lymphocyte count should be at least 1,200 per mm³ or no other evidence of lack of cellular immune competence exists. Vaccination should be carried out a few weeks before the administration of the immunosuppressive treatment for patients undergoing organ transplantation (e.g. kidney transplant). Very few reports exist on disseminated varicella with internal organ involvement following vaccination with Oka varicella vaccine strain mainly in immunocompromised subjects. VARILRIX must not be administered intravascularly or intradermally. Phenylalanine content: The vaccine contains 331 micrograms of phenylalanine per dose. Phenylalanine may be harmful for individuals with phenylketonuria (PKU).

ADVERSE EFFECTS: Very common (≥1/10): pain, erythema. Common (≥1/100 to <1/10): Rash, Pyrexia (oral / axillary temperature ≥ 37.5 °C or rectal temperature ≥ 38.0 °C)†, injection site swelling† Uncommon (≥1/1,000 to <1/100): upper respiratory tract infection, pharyngitis, lymphadenopathy, irritability, headaches, somnolence, cough, rhinitis, nausea, vomiting, viral rash, pruritus, myalgia, arthralgia, Pyrexia (oral / axillary temperature> 39.0°C or rectal temperature> 39.5°C), fatigue, malaise. Rare (≥1/10,000 to < 1/1,000): conjunctivitis, abdominal pain, diarrhea, urticaria.

According to MedDRA (Medical Dictionary for Regulatory Activities) terminology. Injection site swelling and pyrexia were reported very commonly in studies conducted in adolescents and adults. Injection site swelling was also reported very commonly after the second dose in children under 13 years of age.

Version: VRX/API/IN/2025/02 v02 dated 16-Oct-2025

Refer to full prescribing information before prescribing.

Registered medical practitioners can refer company website http://india-pharma.gsk.com/en-in/products/prescribing-information/ for full Product Information.

Please report adverse events with any GSK product to the company at [email protected]

For the use only of a registered medical practitioner or a hospital or a laboratory. Trademarks are owned by or licensed to the GSK group of companies. Refer to full prescribing information before use. Registered medical practitioners can refer company website: india-pharma.gsk.com/en-in/products/prescribing-information/ for Full Product Information. Please report adverse events with any GSK product to the company at [email protected]. ©2026 GSK group of companies or its licensor. For more information, please contact: GlaxoSmithKline Pharmaceuticals Limited, Dr. Annie Besant Road, Worli, Mumbai – 400030 (India).