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The whooping cough epidemic: is the ‘new’ vaccine to blame?

Pertussis (whooping cough) has been a significant cause of morbidity and mortality in young children since the first epidemic was described in 1578. Currently in the West even when infants suffering from the disease are hospitalized and appropriately treated, around 1% still die, and in less developed countries the mortality rate in infants is as high as 4%. However, following the isolation of the causative organism Bordetella pertussis over a century ago, years of research and development resulted in the introduction of an effective vaccine in the 1940s.
The whole cell vaccine used heat-killed bacteria combined with diphtheria and tetanus toxoids to give the classical DPT vaccine, usually given to infants three times during their first year of life with further booster doses twice during childhood. The advent of this vaccine did not prevent the three to five year pertussis epidemic cycle, but it elicited a strong immune response and the total number of cases plummeted in immunized populations. There were some common side-effects, including swelling, mild fever and pain, but these were trivial compared with the high risk of children contracting pertussis if they were not immunized. Sadly, though, very dubious research linked cases of SIDS and encephalopathy with use of whole cell pertussis vaccine, and the popular press eagerly disseminated this dangerously misleading information. Parents began to exercise their so-called ‘freedom of choice’ based on a dearth of unbiased information and stopped having their children immunized, so in the 1990s a new acellular vaccine (DPaT) with fewer side effects gradually replaced the classical DPT.
Now cases of pertussis have more than tripled in the last five years in much of the globe, and the resulting whooping cough epidemic is the worst for 50 years. While it is possible that a more virulent strain of bacterium has evolved, the most likely explanation is that the ‘new’ vaccine is not as effective as its predecessor. Indeed a recent robust study from Australia compared incidence of pertussis in 40,694 children who were immunized in 1998 with either DPT or DPaT (both vaccines were still in use at that time). Significantly higher rates of pertussis were found in the children who had received the latter vaccine.
The suggested solution to the pertussis epidemic is to extend immunisation programmes to cover pregnant women as well as all those who come in contact with young infants. Wouldn’t reintroducing the old vaccine be simpler?