Should my baby have the new chicken pox vaccine?

It’s Thursday morning and you’re just finishing a baby check for Anna, a healthy 8 week old. Her mother Kate asks ‘Just before I go and see the nurse, what do you think about the new vaccine? Is it a good idea?’. For a moment you panic that they’ve changed the 8 week vaccines again…but then Kate carries on ‘When I was little we used to have chicken pox parties, people thought it was a good idea to get it over with. It never did me any harm and babies have such a lot of vaccinations already- is this chicken pox one really needed?’. 

This of course relates to the news that last week the Joint Committee on Vaccination and Immunisation (JCVI) released a statement recommending the inclusion of the chicken pox, varicella vaccine into the routine childhood vaccination schedule for the UK with the aim of preventing severe cases of varicella and reducing complications. To better understand the how, why and when of what they are proposing do read on!

How will the vaccine be given? It proposes the administration of two doses (given at 12 and 18 months), using a combined MMRV vaccine (measles, mumps, rubella and varicella). The JCVI also recommends that a temporary ‘catch up’ programme should be initiated, to prevent a gap in immunity for older children. 

Why is a vaccine needed? As we all know chicken pox is very common, and most of us will have had it at some point during childhood. Recent sero-epidemiology data from the UKHSA suggests 90% of children will have had it by the time they are 10yrs old. For the majority it is an unpleasant but self-limiting illness, with the biggest headache being juggling time off work for the ³5 days exclusion from childcare. However, some will go on to develop serious complications, including bacterial skin infections, iGAS, pneumonia, febrile convulsions, encephalitis, and stroke. In very rare cases it can be fatal. A 2002 British Paediatric Surveillance Study reported the rate of admission with complicated varicella for children as 0.82/100 000 children/ yr. During the pandemic chicken pox rates reduced due to social distancing, meaning a larger pool is currently at risk of infection.

The JCVI considered new (yet unpublished) research from the University of Bristol, looking at the impact of childhood varicella both in the community and hospital setting. The study concluded that complications from severe varicella were ‘common, costly and placed a burden on health services’. 

So, why hasn’t the vaccine been recommended by the NHS before? Historically one of the major arguments against the chicken pox vaccination programme has been the hypothesis that a fall in circulating chicken pox may lead to an increase in shingles in the middle aged/ elderly due to loss of the exogenous boost to their immune system. This risk has been partially mitigated by the roll out of the universal shingles vaccine programme, which will be expanded to cover all adults over 60 within the next 10 years. 

One of the benefits of being late to the vaccine party is that there is real world data available from countries that have a well-established varicella vaccination programme. In 2022 the CDC published data from the first 25 years of the US programme (initially single-dose strategy from 1995, second dose added 2007). 

Overall, varicella disease has declined by >97%, and an impressive 99% in those born since the programme started and severe disease outcomes have been ‘nearly eliminated’. Recent data from the US J Inf Dis 2022 quotes that the vaccine programme prevents 100 varicella related deaths and 10,500 admissions every year. Pregnant women are also more protected; prior to the introduction of the vaccination programme there were approximately 44 cases of congenital varicella syndrome per year reported in the US. CDC reports suggest that this has fallen dramatically with only 3 cases reported between 1995 and 2022. Interestingly, there has been no evidence of a surge in shingles following the introduction of the varicella vaccine in the US.

What about safety? The first dose of combined MMRV vaccine has been associated with a very slight increase in rate of febrile seizures compared to separate MMR and varicella vaccines administered on the same day. The absolute risk is very low, the CDC estimates 1 additional febrile seizure for every 2300 doses given compared to separate vaccines. On balance the JCVI considered that the benefit of a single injection is likely to outweigh this small risk. Importantly, febrile seizures also occur of course with infection. 

So, when will it be delivered? Despite the promising news headlines, it is important to note that the universal vaccination programme is not confirmed yet. The JCVI has submitted its recommendations to the UK governments (it has already been positively received by Public Health Scotland) who will have the final say on if and when to implement the programme. 

In summary, we can tell Kate that there is evidence from the US that a vaccination programme can successfully reduce chicken pox and its complications. The risk of severe disease related to varicella is low, but likely higher than previously reported. This will hopefully become clearer when the Bristol study is published. It is likely that the vaccine will be available via the NHS in the relatively near future but we shall have to wait for confirmation as to when it will be introduced. It is important to remember though that existing guidance on those already entitled to chicken pox NHS vaccination (e.g. non-immune close contacts of someone who is vulnerable, such as children of a parent having chemotherapy, or non-immune healthcare workers) is unchanged.