Australia is seeing a surge in whooping cough cases. So much so that they've released the vaccine for free! California is also requiring teen vaccinations in light of recent whooping cough deaths.
Whooping cough is a respiratory infection caused by a Gram-negative bacterium called Bordetella pertussis. Pertussis is endemic to the United States, with epidemics occurring every 3-5 years and with an average 5000-7000 cases per year. However, since the 1980s, the incidence of whooping cough has increased, with more than 10,450 cases reported in 2007. The last major outbreak occurred in 2005, with more than 25,000 cases. Health officials are hoping to prevent another such outbreak.
Since the 1990s, cases have disproportionately increased in older children and young adults, likely because of anti-vaccine momentum among their parents and possibly evolution of the bacterium itself.
Infants and young children are particularly prone to respiratory and neurological complications from the infection, and deaths are more common among unvaccinated children or those who are too young to be vaccinated. The disease is highly contagious, with 90% of contacts with an infected individual becoming infected themselves. Since the 1990s, cases have disproportionately increased in older children and young adults, likely because of anti-vaccine momentum among their parents and possibly evolution of the bacterium itself.
One challenge to decreasing the incidence of whooping cough in the U.S. is to increase vaccine (DTaP) and booster (Tdap) coverage among both children and adults. The vaccine for pertussis is given in conjunction with the vaccines for diphtheria and tetanus. There are also variations and lower strength doses (such as the booster) for children who cannot tolerate the pertussis vaccine. Children generally get five doses of DTaP (containing full strength dose of pertussis toxin protein): 2, 4, 6, and 15-18 months old and again at 4-6 years of age. A booster (low dose, Tdap) is recommended for adolescents around the age of 11-12 years. The pertussis component can be given in conjunction with a regular tetanus booster (Td) in a single injection. The anti-vaccine movement has raised parents’ fears about a number of disorders being associated with pediatric vaccines, from autism to SIDS, but no medical evidence exists to substantiate these fears.
From 1990-1993, the coverage of the third DTaP dose decreased in the United States to below 90%, even below 85% in 1992. Though it increased back to the mid 90 percent range, it has remained lower than the coverage in the 1980s. A child’s immune system does not develop until roughly 9 months of age, making the third and later doses critical to their long-term immunity against whooping cough. The bacterium can be transmitted to others even before the distinctive cough sets in, making transmission among adults and adolescents who did not receive all of their doses as children highly likely.
Other factors that have led to increased incidence of whooping cough in the U.S. is an adaptation of the pertussis bacteria to survive in vaccinated individuals. The exact mechanism of this adaptation is not clear, possibly linked to the decreased vaccination coverage or adaptation to the immune response, or possibly genetic drift and decreased vaccine efficacy. The vaccine is being updated from a whole cell formulation to an acellular formulation to avoid side effects among some children, but further improvements in the components of the vaccine may be necessary to have an effect on new strains of the pathogen.