FDA Explores Possible Reason for Increase in Whooping Cough Cases

A study conducted by the FDA showed that acellular pertussis (or whooping cough) vaccines are effective in preventing the disease among those vaccinated, but that they may not prevent infection from the pertussis-causing bacteria in those vaccinated or its spread to others, including those who may not be vaccinated.

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Two types of pertussis vaccines exist: whole-cell and acellular. Whole-cell pertussis vaccines contain a whole-cell preparation of a killed B. pertussis  bacteria. The acellular pertussis vaccine is more purified and uses only selected portions of the bacteria to stimulate an immune response in the patient.

The FDA conducted a study in baboons to explore the possibility that although acellular pertussis vaccines protect against disease, they might not prevent infection.

The scientists vaccinated one group of baboons with a whole-cell pertussis vaccine and the other group with an acellular pertussis vaccine currently used in the U. S. The animals were vaccinated at ages 2, 4, and 6 months. 

The results showed that both types of vaccines generated robust antibody responses in the animals, and none of the vaccinated animals developed outward signs of pertussis after being exposed to B. pertussis. 

However, researchers noted differences in other areas of immune response. Baboons that received an acellular pertussis vaccine had the bacteria in their airways for up to 6 weeks and were able to spread the infection to unvaccinated animals. In contrast, baboons that received whole-cell vaccine cleared the bacteria within 3 weeks.

The study demonstrated that although those immunized with an acellular pertussis vaccine may be protected from disease, they may still become infected with the bacteria without always getting sick. Also, they are able to spread infection to others, including young infants who are susceptible to pertussis.

Results of this study are published in The Proceedings of the National Academy of Sciences (PNAS).

For more information call (202) 334-2679 or visit the PNAS website

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