IT鈥橲 a unique public health conundrum,and a stark reminder of how difficult it is to eliminate even the most mundane diseases. As more countries start to vaccinate against chickenpox, they will unwittingly encourage the spread of shingles, which mainly afflicts older people.
In the US, most children are vaccinated against chickenpox. Canada is poised to follow, and several other countries, including Australia, are considering vaccination. But there鈥檚 a catch: it turns out that stopping chickenpox in children means that millions of adults will develop shingles in later life.
After a bout of chickenpox, the virus remains lurking inside the sensory nerves. It stays there until a fall in immunity, usually after the age of 60, allows it to flare up again. The result is shingles, a painful rash that strikes a quarter of chickenpox veterans. In some 20 per cent of cases shingles leads to severe, lasting pain.
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But in an upcoming issue of the journal Vaccine (vol 20 p 2500), Marc Brisson and his team at the Public Health Laboratory Service in London will report that in England, adults living with children are less likely to develop shingles than those who do not. At present, exposure to children means re-exposure to chickenpox, which acts like a booster vaccine against shingles, says John Edmunds, a member of the team.
But if all children are vaccinated for chickenpox, adults who have had the disease will not be exposed to enough ofthe virus to prevent full-blown shingles later. The PHLS team calculates that over the first 50 years, vaccinating a population the size of the US would save 5000 children from dying of the complications of chickenpox. But an extra 5000 people over 60 would die of the complications of shingles, and there would be 21 million extra cases.
鈥淰accination looks good in terms of costs and benefits if you just look at the economic effect of chickenpox,鈥� says Edmunds, especially the time parents take off to care for sick children. 鈥淏ut shingles has been ignored. If you include that, the costs and benefits may not bevery good at all.鈥�
Vaccination against chickenpox is not widespread in Europe, as the disease is regarded as fairly harmless. But in the US, where vaccination was introduced in 1995, chickenpox cases have fallen by up to 80 per cent. 鈥淚 started to support vaccination for chickenpox when I started seeing more deaths from Group A streptococcus infections,鈥� says Michael Oxman of the University of California at San Diego. These bacteria, the main complication of chickenpox in children, can cause toxic shock and the flesh-eating disease necrotising fasciitis, and are becoming more virulent.
Oxman concedes that chickenpox vaccination could lead to a surge in shingles, as the PHLS team suggest. One remedy could be to vaccinate older people as well, to boost their immunity to shingles. Oxman is heading a double-blind study of 40,000 Americans over 60, to be completed in 2004, to see whether this works. But even if it does, Edmunds foresees problems in getting adults, especially older men, to take their shots.