Should more countries vaccinate children against chickenpox?

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

It is a routine childhood jab in some countries – including the US, Canada, 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, such as older people at risk of shingles.

Fortunately, growing evidence suggests that such harms aren’t materialising. What’s more, an analysis published today finds that, overall, the vaccine does more good than harm. So, is it time for the chickenpox vaccine-resistant countries to come round?

Chickenpox is caused by a 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 may 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 per cent 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 per cent 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 per cent 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 per cent, 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, says Manjiri Pawaskar at Merck in Rahway, New Jersey. “It poses a significant caregiver burden,” she says.

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, says a spokesperson for the UK Health Security Agency.

For adults that have experienced 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.