Varivax, manufactured by Merck Sharp & Dohme was introduced in 2024 to vaccinate against chicken pox. Despite the low risk chickenpox presents to children, the HSE added the chickenpox vaccine to the routine childhood vaccination schedule in 2024, to counter societal costs such as “leave from paid work to care for sick children”. The HSE recommend two doses for babies at 12 months and in junior infants.
This article provides an overview of the potential risks associated with both the vaccine and the diseases it targets, helping you make an informed decision.
Disease versus Vaccine Risk Summary
Risk from chickenpox disease
Risk of hospitalisation from chickenpox
Pre vaccine: approx 1 in 57,000 (0.002%) all ages
Pre vaccine: approx 1 in 9,000 (0.01%) under 5s
Risk of death in Ireland pre vaccine (2012 to 2021)
Pre vaccine: approx 1 in 4 million (0.00003%) for all ages
Zero deaths in under 5s since 2000
Risks from each dose of chickenpox Varivax vaccine
2 doses recommended, at 12 months and in junior infants (Side effects as per Varivax patient information leaflet Dec 2023)
Observed side effects post administration of Varivax (post marketing)
Illnesses affecting the nervous system (brain and/or spinal cord) such as sagging facial muscles and drooping eyelid on one side of the face (Bell’s palsy), walking unsteadily, dizziness, tingling or numbness of the hands and feet
Inflammation of the brain (encephalitis), inflammation of the coverings of the brain and spinal cord not caused by bacterial infection (aseptic meningitis)
Shingles, sore throat (pharyngitis), purple or red-brown spots visible through the skin (Henoch-Schönlein purpura)
Secondary bacterial infections of the skin and soft tissues including impetigo and cellulitis
Varicella (chickenpox), aplastic anaemia, which may include bruising or bleeding more easily than normal
Red or purple, flat, pinhead spots under the skin
Severe paleness
Bruising or bleeding more easily than normal; red or purple, flat, pinhead spots under the skin
Severe paleness
Severe skin rash (ulcers and blistering that may involve the eyes, mouth, and/or genitals)
Often itchy spots which start on the limbs and sometimes on the face and the rest of the body (Stevens-Johnson syndrome; erythema multiforme)
Muscle weakness, abnormal sensations, tingling in the arms, legs, and upper body (Guillain-Barré syndrome)
Fever, feeling sick, vomiting, headache, stiff neck and sensitivity to light (meningitis)
Stroke
Seizures (fits) with or without a fever
Risk Category
Observed Side Effects
Up to 1 in 10,000 (0.01%)
Swollen glands, bruising or bleeding more easily than normal
Agitation, sleeping too much, difficulty walking, seizures with a fever, shaking
Swelling of eyelid, irritation of eye
Ear pain
Feeling of fullness in the nose sometimes with throbbing ache and facial pressure or pain (sinusitis), sneezing, congestion in the lung, runny nose (rhinitis), wheezing, swelling of the tubes relating to the lungs (bronchitis)
Lung infection, severe lung infection with fever, chills, cough, congestion and shortness of breath (pneumonia)
Flu-like illness
Stomach pain, upset stomach and feeling sick, blood in the stool, mouth ulcer
Flushing, blisters, skin disorders (including bruising, and hives)
Muscle/bone pain, aching muscles, stiffness
Injection site reactions including changes in skin colour and hive-like rash
Up to 1 in 1,000 (0.1%)
Headache, drowsiness
Discharge and itching of the eyes
With crusting of eyelids (conjunctivitis)
Cough, nasal congestion, chest congestion, runny nose, loss of appetite
Upset stomach with vomiting, cramps, diarrhoea caused by a virus
Diarrhoea, vomiting (gastroenteritis)
Ear infection, sore throat
Crying, inability to sleep, sleep disorders
Varicella skin rash caused by virus (chicken pox), illness caused by a virus, inflammation of the skin, redness of the skin, hives
Weakness/fatigue, generally feeling unwell, injection site reactions including numbness, bleeding, bruising, hardened raised area of the skin, warm feeling, warm to touch
Rash, rash with flat, red skin and small confluent bumps, varicella-like rash
Injection site rash, itching at injection site
Up to 1 in 10 (1% to 10%)
Fever
Injection site redness, pain/sensitivity to touch/soreness and swelling
Some other special warnings and precautions
Should not be given if child is allergic to antibiotic neomycin
What is Chickenpox?
Chickenpox is a common, mild, and highly contagious illness that primarily affects children but can occur at any age. Medically known as varicella, it is caused by the varicella-zoster virus. The infection is more prevalent in winter and spring, especially between March and May. Chickenpox presents as a red, itchy rash that develops into fluid-filled blisters, which eventually crust over and form scabs that fall off. New spots may continue to appear in waves over 3 to 5 days after the rash begins. Before the rash appears, mild flu-like symptoms, such as nausea, a fever of 38°C or higher, muscle aches, headaches, loss of appetite, and general discomfort may occur. These symptoms, particularly fever, tend to be more severe in adults than in children. Chickenpox is contagious from about two days before the rash starts until all blisters have crusted over. After recovering, the virus remains dormant in the nervous system and can reactivate later in life as shingles.
For most children, chickenpox is a mild illness that resolves on its own, with complications being rare and more likely to affect adults. Chickenpox parties were common not so long ago, where parents deliberately exposed children to the virus to have them contract the disease at a younger, less risky age and build immunity.
Well nourished children have little to fear from chicken pox and perhaps something to gain. This study from the University of Berne, Switzerland [Introduction – 4] reviewed these fever inducing (i.e. febrile) infections and concluded “study consistently revealed a lower cancer risk for patients with a history of FICD [febrile infectious childhood diseases].”
What is the risk of hospitalisation from chickenpox in Ireland?
The risk of hospitalisation from chickenpox for under 5s is approximately 1 in 9,000 (0.01%). Cases in the table below include both confirmed and suspected cases of chicken pox. There is no data for admission to intensive care units.
What is the risk of death from chickenpox in Ireland?
The risk of death from chickenpox in Ireland has always been very low. In the decade 2012 to 2021, the risk of death was approximately 1 in 4 million (0.00003%) for all ages. All of these deaths were in those aged over 70. There were zero deaths for under 5 year olds in this period.
Does the Varivax vaccine guarantee protection against chickenpox?
No. As with all vaccines and as stated on the patient information leaflet, protection from the disease cannot be guaranteed. Chickenpox type rash is listed as a common side effect on the patient information leaflet, affecting 1 in 10 people.
When the costs of the booster dose for varicella and the increased shingles recurrences are included, the universal varicella vaccination program is neither effective nor cost-effective.
Additional Safety Data for Varivax
As with all medicines, vaccines come with side effects, sometimes very serious. Parents need to research every vaccine to ensure benefits outweigh the risks.
“Severe allergic reactions can occur to any vaccine but they are very rare and are usually seen in less than 1 in 10,000 people who are vaccinated” [Menitorix PIL, 11/2016]
Varivax is a live virus vaccine and has the potential to shed. The following warning is written on the patient information leaflet: In rare circumstances, it is possible to catch chickenpox, including severe chickenpox, from a person who has been vaccinated with VARIVAX.
