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Weighing the risks to older people if more children are vaccinated against chicken pox

Although some countries are concerned that vaccinating children could lead to a rise in severe chickenpox cases among older unvaccinated people, a recent study has found that on the contrary, routinely immunising children could slash – across all ages – the number of people who die from the infection.

Vaccines sometimes generate ill-founded health scares, but whether to immunise against chickenpox has long been the subject of genuine medical debate.

It is a routine childhood jab in some countries – including the US, Canada, South Africa, Australia, Japan and about half of Europe – but hold-outs include the UK, Denmark, France, Portugal and several Scandinavian nations. There are concerns that while introducing the childhood vaccination would be beneficial for those who receive it, it may be detrimental for others, like older people at risk of shingles.

Fortunately, growing evidence suggests that such harms aren’t materialising. What’s more, a recent analysis found that, overall, the vaccine does more good than harm.

So, it might be time for the chickenpox vaccine-resistant countries to change their mindsets, writes Clare Wilson in New Scientist.

Chickenpox is caused by the highly infectious virus called varicella zoster. In the absence of vaccination, most people get infected in childhood and usually have a mild illness, with the main symptoms being an itchy, blistering rash.

In fact, the younger a person is when they catch it, the milder their experience tends to be. Some families even deliberately expose their children to others who are infected to “get the illness over with”.

But the virus can occasionally cause severe symptoms – for instance, if it triggers bacterial infections – and can even be fatal, especially in those with weak immune systems.

When the first chickenpox vaccine was developed three decades ago, one concern was that while it would benefit the children who received it, some parents might not get their children vaccinated. A routine vaccination programme would mean that population-level immunity would be relatively high, so those who missed out might not encounter the virus until they were in their teens or older, raising the risk of severe complications compared with a childhood infection.

Another fear was the impact on older people. After a chickenpox infection, the virus’ DNA remains in nerve cells and it can reactivate in later life, leading to the painful and debilitating symptoms of shingles. It is thought that chickenpox infections among children expose adults to small doses of the virus, boosting their immunity and making them less likely to develop shingles.

Despite the concerns, the US began offering the vaccine routinely to children in 1995, with other countries later following suit. Those that held out are now able to see the results, which suggest that introducing the vaccine was the right decision.

Several studies over the past few years have shown that the US and other countries haven’t seen an increase in shingles cases. A UK study found that if adults are exposed to a child with chickenpox in their household, their reduction in shingles risk is less than previously supposed, with a fall of about 27% over 10 to 20 years.

Now, data from such studies have been plugged into a standard set of equations that predict the impact of vaccines on rates of infections and illness.

This has been used to model the effects over 50 years if the vaccine were to be offered routinely to children in Denmark.

The researchers – which included scientists at Merck, a manufacturer of one of the vaccines, and Aarhus University Hospital in Denmark – found that while there would be about a 1% rise in shingles cases for the first few years after the introduction of vaccination, after 50 years, the total number of cases would be 9% lower than expected if Denmark were to continue not to vaccinate.

They also found that the number of people of any age who die or need hospital treatment for chickenpox would be cut by more than 90%, countering the idea that there would be a rise in more severe cases from unvaccinated people catching the virus while older.

Vaccination programmes would also avoid some of the less obvious harms from this virus, including children missing school and parents having to take time off work, said Manjiri Pawaskar at Merck in New Jersey, US. “It poses a significant caregiver burden,” she said.

Several countries, including the UK and Denmark, are now considering adding the chickenpox vaccine to the routine childhood jabs on offer. At the moment, many such countries let people pay for the vaccine privately, but this means uptake is low. The UK’s vaccine advisory panel, the Joint Committee on Vaccination and Immunisation, will take any new data into consideration, said a spokesperson for the UK Health Security Agency.

For adults who had chickenpox as a mild illness, it may be tempting to dismiss the need for vaccination against this condition. But one thing that the Covid-19 pandemic has shown is that even if an illness severely affects only a small percentage of the population, it can lead to appreciable harms on a country-wide scale and is worth taking countermeasures against.

Perhaps it is time for more countries to stop giving the chickenpox virus a free pass.

Study details:

Universal varicella vaccination in Denmark: Modeling public health impact, age-shift, and cost-effectiveness

Colleen Burgess, Salome Samant, Thomas leFevre, Carsten Schade Larsen, Manjiri Pawaskar.

Published in PLOS GLOBAL Public Health on 5 April 2023


We modelled the long-term clinical and economic impact of two-dose universal varicella vaccination (UVV) strategies in Denmark using a dynamic transmission model. The cost-effectiveness of UVV was evaluated along with the impact on varicella (including age-shift) and herpes zoster burden. Six two-dose UVV strategies were compared to no vaccination, at either short (12/15 months) or medium (15/48 months) intervals. Monovalent vaccines (V-MSD or V-GSK) for the 1st dose, and either monovalent or quadrivalent vaccines (MMRV-MSD or MMRV-GSK) for the 2nd dose were considered. Compared to no vaccination, all two-dose UVV strategies reduced varicella cases by 94%-96%, hospitalisations by 93%-94%, and deaths by 91%-92% over 50 years; herpes zoster cases were also reduced by 9%. There was a decline in the total number of annual varicella cases in all age groups including adolescents and adults. All UVV strategies were cost-effective compared to no vaccination, with ICER values ranging from €18,228-€20,263/QALY (payer perspective) and €3,746-€5,937/QALY (societal perspective). The frontier analysis showed that a two-dose strategy with V-MSD (15 months) and MMRV-MSD (48 months) dominated all other strategies and was the most cost-effective. In conclusion, all modeled two-dose UVV strategies were projected to substantially reduce the clinical and economic burden of varicella disease in Denmark compared to the current no vaccination strategy, with declines in both varicella and zoster incidence for all age groups over a 50-year time horizon.


PLOS GLOBAL Public Health article – Universal varicella vaccination in Denmark: Modelling public health impact, age-shift, and cost-effectiveness (Open access)


New Scientist article – Should more countries vaccinate children against chickenpox?


See more from MedicalBrief archives:


Chickenpox vaccine reduces incidence of paediatric shingles


Anti-vaxxers blamed for large North Carolina chickenpox outbreak


Shingles vaccine may also reduce stroke risk


The anti-vaxxer myth has ‘become tiresome’








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