In November 2023 the UK’s Joint Committee on Vaccination and Immunisation (JCVI) announced that it was recommending a “universal varicella (chickenpox) vaccination programme” to be introduced as part of the routine childhood schedule. The programme would comprise 2 doses of the combined MMRV (measles, mumps, rubella, and varicella) vaccine, offered at 12 and 18 months. This recommendation follows the evidence from other countries that a 2-dose schedule decreases the number of varicella cases in childhood “rapidly and dramatically”.
Chickenpox in childhood
Varicella, known as chickenpox, is a “highly contagious infectious disease” caused by the varicella zoster virus. Symptoms include an itchy, spotty rash, a fever, and general malaise. JCVI states that it is a “very common” disease that “affects most children during childhood”. However, it can be caught at any age. It is transmitted through direct contact with infected people or through airborne droplets.
Although most varicella cases in children are “relatively mild” and resolve without medical interventions, some children can develop complications such as bacterial infection of skin lesions, or encephalitis or pneumonitis. It is most serious in “very young infants” under the age of 4 weeks, and in adults. Data from the UKHSA suggest that “approximately half of children” have had varicella by the time they reach 4 years old; this increases to 90% by the age of 10. Thanks to COVID-19-related restrictions, fewer cases of varicella were identified; this leaves a “larger pool of children” susceptible.
Herpes zoster, or shingles, is triggered when the varicella zoster virus is reactivated in a previously infected person. This is a risk because the virus remains dormant after an initial infection. People with herpes zoster can transmit the virus to susceptible people to cause chickenpox.
What is currently in place?
The JCVI reports that the UK has had a universal shingles vaccination programme in place since 2013 for adults. The programme was updated in September 2023 and includes:
- Adults turning 65 years of age
- Adults aged 70 and over
- Adults over the age of 50 with a severely weakened immune system”
In 2009 the JCVI considered strategies to protect against varicella and herpes zoster, electing not to recommend varicella vaccination.
“It was agreed at the time that this recommendation should be reviewed when further information relating to varicella epidemiology, vaccination, and exogenous boosting were available.”
What’s changed?
The varicella-zoster JCVI sub-committee has met “multiple times” over the past two years to review updated evidence on disease burden, potential effect on exogenous boosting, updated seroprevalence data, and modelling cost-effectiveness and real-world data from countries with programmes in place. The main JCVI then discussed these updates in October 2023.
Disease burden
The JCVI states that “errors in coding” confuse estimations of the true extent of hospitalisations caused by varicella. As hospitalisations are “frequently” due to secondary complications they are not always recorded as related to varicella. Furthermore, there may be other secondary complications that are less understood than the recognised cellulitis, invasive group A streptococcal infection, or childhood stroke. Complications from severe varicella are common, costly, and burdensome on health services.
Real-world experience
The JCVI can always draw on the experience of several countries with varicella vaccination in their routine vaccine schedules, such as the USA, Canada, Australia, and Germany. These countries have observed “significant” effects on cases and hospitalisations. Data were reviewed and incorporated into modelling work to investigate the “true extent” of the potential effect of vaccination on exogenous boosting.
Cost-effectiveness modelling
The JCVI sub-committee reviewed and provided input parameters for unpublished research carried out by the University of Cambridge. It was agreed that “previous assumptions” on the duration of protection from herpes zoster through exogenous boosting was too long. Cost-effectiveness analysis revealed that a routine childhood programme would be cost effective and possibly cost saving, depending on the vaccine price obtained.
The recommended vaccination programme
There were two options for varicella vaccination: a varicella-only product or as a combination with measles, mumps, and rubella, as MMRV. The proposed schedule involves two doses at 12 and 18 months. This coincides with times already reserved for the MMR vaccine according to upcoming changes to the routine infant schedule. This would mean that fewer injections are required per single immunisation visit, which is preferred among parents.
JCVI recognises an “increased risk” of febrile seizures but describes the “absolute risk” as “very low”. This is “not of clinical concern” particularly in contrast to the “considerable benefit” of reduced injections.
There is also potential to implement a catch-up vaccination programme, following the implementation of a routine programme. The committee considered this “beneficial” to prevent a gap in immunity. However, more work is needed to understand the cost-effectiveness of this programme.
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