One of the small mysteries that has puzzled doctors of late has been the rise in the incidence of whooping cough (sometimes called pertussis) in the industrialized world, despite the existence of a long-standing vaccination program against it. (I had the vaccine as a child; at the time, it was the ‘P’ in the DPT combination vaccine, which protected against diphtheria, pertussis, and tetanus.) Now, according to an article at the “Short Sharp Science” blog at New Scientist, a research team at the University of New South Wales, in Australia, may have discovered at least a part of the answer.
According to The Daily Telegraph of Sydney, “the research team analysed more than 200 samples of the bacterium collected over the past 40 years in Australia and compared them with samples from Japan, Canada, USA and Finland”. They found that there are at least two strains that the vaccine may not protect against – known as MT27 and MT70.
The original vaccine, licensed in 1949, was a “whole-cell” vaccine, containing whole killed Bordetella pertussis bacteria, the organisms that cause whooping cough. But beginning in 1997, the original vaccine was phased out in favor of a new, “acellular” vaccine, which contains only selected antigens from B. pertussis. In their paper [abstract + PDF], published in the journal Emerging Infectious Diseases, the research team describes their use of genetic analysis to identify at least two new strains of the bacterium. Because the new strains have mutated slightly, the antigens they produce do not match the antigens for which the new vaccine “primes” the immune system. The old vaccine, because it included the whole B. pertussis organism, provided several hundred antigens, giving a wider range of protection. (Even if an infectious organism had mutated to change a few antigens, there would be many left by which the immune system could recognize the invader.)
As the research team emphasizes, vaccination is still very important, because pertussis is a very dangerous disease, and even imperfect protection is considerably better than none. Their results may remind us, though, that we need to try to consider all the consequences of introducing new or changed therapies, because there’s probably still no free lunch.