Incidence of chickenpox fell over the pandemic, but now it is coming back – Michael McHale talks to specialist public health doctors about the threat that chickenpox poses to people who have a compromised immune system
Like so many infectious diseases, cases of chickenpox appear to have fallen sharply during the height of the Covid pandemic, when lockdowns kept social interactions to a minimum.
However, the reopening of Irish society has raised concerns that the country may be experiencing a spike in cases of the infection, caused by the varicella-zoster virus.
In 2020 there were just 25 hospitalised cases recorded in Ireland, and 23 the following year. Cases increased as restrictions eased, with last year seeing 76 cases in clinical settings. This was still down on pre-pandemic levels of infection, with 93 cases recorded in 2019.
However, according to the Health Protection Surveillance Centre (HPSC), 31 hospitalised cases have been found in the first two-and-a-half months of this year (up to March 18), 22 cases more than the same period in 2022, suggesting that overall hospital presentations of the condition may surpass the 100 mark this year.
“In the early part of last year, things were still very restricted – I think that (the figures) reflects that activity,” Dr Suzanne Cotter, specialist in public health medicine at the HPSC, told Irish Medical Times. “So it is back up now, and whether it’ll exceed 2019, we’ll have to wait and see.”
While chickenpox is mostly found in children, (the vast majority of whom make a full recovery from their infection) the risk of complications is greatest among those with an underlying condition.
“Every year we would see, on average, three or four cases of encephalitis or cerebellitis – some inflammation of the brain or cerebellum occurring after chickenpox,” Dr Bridget Freyne, paediatric infectious diseases consultant at Children’s Health Ireland, said.
Other rare complications she has seen include meningitis and strokes, but Dr Freyne is particularly concerned by the risk of vulnerable children contracting a secondary bacterial infection such as group A strep – another infectious illness that is on the increase in Ireland, with 117 cases reported to the HPSC in the first two-and-a-half months of this year.
“There’s a known association that group A strep can get in via chickenpox lesions and cause really nasty cellulitis, but can also spread to cause sepsis.”
These life-threatening complications are the main reason behind why many paediatric infectious disease specialists like Dr Freyne would be supportive of the introduction of the chickenpox vaccine into the HSE’s childhood vaccination schedule. Currently the inoculation is only available privately, costing parents around €180 for the two-dose programme.
Last June the Health Information and Quality Authority (HIQA) announced the setting up of a health technology assessment (HTA) into whether the jab – known as the varicella vaccine – should be added to the list of vaccinations routinely given to children at a young age. A statement by HIQA on the announcement said that ‘the HTA will assess the clinical effectiveness, cost-effectiveness, budget impact, ethical and social aspects, and organisational changes associated with an expansion of the childhood immunisation schedule to include chickenpox vaccination’.
The assessment was requested by the Department of Health and supported by the National Immunisation Advisory Committee. HIQA is expected to publish their findings in the coming months, which will inform a Government decision on whether the vaccine should be included in the childhood schedule.
The varicella vaccine can be given to children over 12 months. It is at least 90 per cent effective at preventing the disease and 100 per cent effective at preventing severe complications.
“Even people who do get a breakthrough infection, they usually get a mild infection,” Dr Freyne added. “It is on the standard schedule in many countries for that reason. Certainly, it’s something that we would advocate for.”
Widespread use of the vaccine would also have a significant impact on many children who may not be in a position to get the jab themselves, primarily because of a weakened immune system caused by another condition.
“If children are going to start on a course of immune suppression of chemotherapy, they will be tested to see if they are immune to chickenpox, and if not, they will get the vaccine,” Dr Freyne explained.
“The problem is you can’t give it to children who are already immunosuppressed for reasons like a sudden diagnosis of leukaemia, so often for those children it’s too late.
“We would recommend, sometimes, chickenpox vaccine as part of post-exposure prophylaxis. If somebody lives in a family where there’s somebody who is immunocompromised, and they’ve had contact with someone with chickenpox, they could be given the vaccine to try and prevent them developing chickenpox and bringing it into their household.”
Of all patients hospitalised with chickenpox, the majority are under the age of five, according to Dr Cotter, “but we have seen representation from all age groups actually, including older children and adults.” In her experience, most exposure to the infection takes place naturally in the community by chance, as opposed to parents encouraging the spread of the infection through so-called ‘chickenpox parties’ or other gatherings.
As a consultant in infectious diseases in Beaumont Hospital, Dr Eoghan de Barra has seen first-hand the debilitating effects the condition can have on adults, and the two main strands of illness that the infection can cause.
“One is reactivation – so that is shingles. Particularly, certain immunocompromised people can get a really nasty reactivation. The other is, if you never had chickenpox as a child – which is very rare if you were born and bred in the Northern Hemisphere, but if you came from India or Sub-Saharan Africa you may not have had chickenpox – and you get primary chickenpox as an adult, you can get very sick.”
Antiviral medications such as aciclovir are available to address the more severe symptoms caused by either a new infection or reactivation in adults. Varicella-zoster immune globulin (VZIG) is also recommended for post-exposure prophylaxis and treatment in particularly for vulnerable people who have not previously had chickenpox, such as pregnant women. Should a child be born within a week of their mother having an infection, they are also likely to be treated with VZIG.
When it comes to reactivation, Dr de Barra points to the shingles vaccine as an important tool in fighting the condition.
“About a third of people who get shingles will end up with what’s called post-herpetic neuralgia – that’s pain in the area afterwards,” he explained. “Early recognition and early therapy with the antivirals seems to reduce that.
“The other big intervention is the shingles vaccine, which is a booster, if you like, to the immunity you had from having chickenpox as a child. That’s also available in Ireland and it’s recommended for certain at-risk groups, but it’s probably not being that widely used as yet.”
Guidelines from the National Immunisation Advisory Committee state that the shingles vaccine can be given to people aged 50 years and older, or to those over 18 who are at an increased risk. However, the inoculation is not available through the HSE’s medical card or drug payment schemes.
Both Dr de Barra and Dr Freyne are members of the Infectious Diseases Society of Ireland, which holds its annual scientific meeting in Croke Park on Thursday and Friday, May 18 and 19. Clinicians can register to attend or submit a research abstract at www.idsociety.ie.