Should the UK introduce a universal childhood varicella vaccination programme?

Primary varicella infection (chickenpox) is common in the UK with over threequarters of parents reporting a history of chickenpox in their children by 5 years of age. Following primary infection, the varicella zoster virus (VZV) remains dormant in the dorsal root ganglia and reactivates in later life following a decline in cell-mediated immunity to cause herpes zoster or shingles (HZ). Although chickenpox is generally mild and selflimiting in healthy children, secondary bacterial infections, pneumonia and neurological complications can occur. The risk of severe chickenpox is higher in immunocompromised individuals, pregnant women and neonates, although most hospitalisations for severe complications are in previously healthy children. Shingles is a potentially debilitating condition, which results in a greater burden and quality of life loss than chickenpox. The incidence of shingles and the risk of post herpetic neuralgia increase with age. Safe and effective live-attenuated varicella vaccines (Oka VZV strain) have been available for the prevention of chickenpox since the 1980s; two doses have a reported effectiveness between 84% and 98%. Countries across Europe, North America and Australia have adopted different approaches to using vaccine for VZV control. While some countries, such as Australia and the USA, have introduced routine childhood varicella programmes using one or two dose schedules, many European countries (including the UK and Belgium) have not. In the UK, a selective vaccination policy has been recommended, offering vaccine to high-risk groups including non-immune healthcare workers and susceptible household contacts of immunosuppressed individuals. The USA, which initially introduced a one-dose varicella programme in 1995, saw a significant decline in varicellarelated deaths in 1–4 year olds (92% fall between 1990–1994 and 1999–2001), hospitalisations (88% fall between 1994/ 1995 and 2002) and ambulatory visits (59% fall between 1994/1995 and 2002). Similar declines have been observed in other countries using a one-dose schedule such as Australia. A potential concern with a one-dose programme where sufficiently high coverage is not achieved, however, is a shift in the average age at infection to older age groups where the disease is likely to be more severe. In the USA where coverage in the early years was suboptimal, the average age at infection increased from 3–6 years in 1995 to 9–11 years in 2005, although the age-specific incidence decreased in all age groups. Despite the success of the one-dose programme in the USA, breakthrough infections and outbreaks in vaccinated populations were observed and in 2006, given the evidence of higher vaccine effectiveness, a two-dose policy was adopted. Because of an increased risk of febrile seizures observed with combined measles, mumps, rubella and varicella vaccine at 12–15 months of age, the Centers for Disease Control and Prevention currently recommends that the first dose be offered as a monovalent vaccine with the combined vaccine used for the second dose at 4–6 years of age. In the first five years after the second dose was introduced, varicella incidence reached the lowest since the start of the vaccine programme (declining around a further 70%), with fewer outbreaks and severe cases. For a vaccine to be recommended for inclusion into the UK routine schedule, evidence of cost effectiveness is required. Accurate assessment of the burden of disease is essential to inform this cost effectiveness. Blumental and colleagues studied varicella-related hospitalisations in 101 hospitals (representing 97.7% total paediatric beds in Belgium) over 1 year. The incidence of paediatric varicella hospitalisations was estimated at 29.5 per 100 000 person-years—highest in children aged 0–4 years. This compares with a recent retrospective study in England that found rates of hospitalised varicella of 31.2 per 100 000 children aged 0–15 years in 2010/2011. The majority of Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK Correspondence to Dr Gayatri Amirthalingam, Immunisation, Hepatitis and Blood Safety Department, Public Health England, 61 Colindale Avenue, London NW9 5EQ, UK; [email protected]