September 15, 2010

Return of Whooping Cough Worries Americans

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Most Americans feel the prick of a pertussis vaccination when they are as young as two months old.  While the medical community largely considered pertussis – or whooping cough – to be eliminated in 1976 (with less than 1,000 cases in the United States), the disease has resurged in Michigan, South Carolina, New York and California, where the outbreak has reached the level of an epidemic with 2,774 reported cases.

Caused by the bacterium, Bortadella pertussis, the disease is highly contagious. The main symptom is a cough, which develops into uncontrollable coughing fits, each with five to 10 forceful coughs.  These fits are followed by a high-pitched “whoop” sound as the patient struggles to breathe.

Pertussis is most prevalent in young children who have not yet received their full course of vaccinations — five DTap (Diptheria, Tetanus, and pertussis) vaccines administered between ages two months and six years.

Though most healthcare professionals remain confident in the vaccine, it is not clear what is causing the unexpected rise in the number of cases, especially in adults and adolescents who have already been vaccinated.

According to Dr. Roy M. Gulick, Professor of Medicine at the Weill Medical College, the occasional rise of pertussis may be part of a cyclical pattern. “Prior to the availability of vaccines, pertussis cases occurred in cyclic peaks and that pattern may be occurring again.”

Another explanation may be reduced vaccine efficiency.

“The bacteria may have evolved to escape the vaccine, and the current vaccine is not necessarily the best one,” said Prof. Avery August, microbiology and immunology. “It has [also] been known for some time that the vaccine does not give permanent protection.”

An outbreak can jeopardize the vaccine’s effectiveness further, making people, especially teenagers and adults, more susceptible to the disease.

According to Heather M. Stone, Public Health Communications Specialist at Gannett Health Services, “The antibody protection developed from a childhood DTaP vaccination series eventually wanes.  This means that without a booster vaccine, adolescents, teens and adults are susceptible to a pertussis infection, especially during an outbreak.”

The rise in reported cases may also be attributed to technological improvements. According to August, more efficient testing and surveillance has made it easier for doctors to determine that a patient is infected with pertussis. “Testing for pertussis has become easier and more efficient (and perhaps cheaper) so more tests are ordered that confirm the bacterial infection.”

Though the disease most typically affects young children, since 2006, more than half of the reported patients have been adults. This may be because a booster vaccine has typically not been offered to anyone past the age of 7.

According to Gulick, “Prior to 2006, pertussis booster vaccines were not recommended routinely for adolescents or adults. A pertussis booster vaccination [Tdap – a booster vaccine for Tetanus and Diptheria now contains a booster for pertussis] is now recommended for adolescents and adults by the Advisory Council on Immunization Practices.”

According to Dr. Stephen Hughes, Gannett’s Associate Director for Medicine, the vaccine used for children younger than 7 years (DTaP) has a slight difference in formula from the Tdap vaccine.  “DTaP contains a greater amount of the acellular pertussis component than the Tdap vaccine.  A smaller amount is necessary in a booster pertussis vaccine as the body has already been introduced to the virus and only requires a “reminder” for building adequate protection,” he said.

After initial inoculations and subsequent boosters, contact with the disease helps increase immunity as well.  According to Hughes, “Coming into contact with the disease provides an opportunity for the body to refresh, or ‘boost’ its antibody response.  For some diseases, the more often this occurs the longer the body will be effective at protecting itself from illness.  As vaccination rates rise and less disease is circulating, there is less opportunity for exposure-related ‘booster effects.’”

When immunity rises, the number of cases decreases, and the number of opportunities to come in contact with the disease decreases too, thus eventually lowering immunity as well. This may contribute to the cyclical nature of the disease and explain why it is extremely important to stay on schedule when it comes to recommendations for vaccinations.

A booster vaccine, though effective, might not be the best solution for preventing outbreaks. According to August, “[The booster] might be helpful but that does not get around the underlying issue that the current vaccine is not ideal. A new vaccine with different components might be best. The current vaccine could be altered to make it more efficient and effective. Basic research in animal models of this disease has shown that it is possible, and it will take some time for that to be translated to use in humans.”

While doctors have reported cases of pertussis in upstate New York, healthcare professionals at Gannett remain confident that young children are still most at risk.

“Cornell students working with children should be aware of their immunization records, in particular.  If [they] come into contact with children (even just occasionally), [they] should be sure to stay up to date with all vaccinations to help reduce the risk of transmitting an illness to those who are often most vulnerable,” Stone said.

Gannett is closely monitoring the situation and its implications for the Cornell community.

Original Author: Maria Minsker