WEDNESDAY, SEPTEMBER 28, 2016

Whooping cough antigen disappearing from U.S. bacteria

An antigen used in whooping cough vaccines is now absent from more than half of all isolates of Bordatella pertussis, according to a study recently published ahead of print in Clinical and Vaccine Immunology.

Vaccines for whooping cough, which is also known as pertussis, contain three to five protective antigens. The presence of the antigens are important to ensure the vaccine is effective. One of the antigens, pertactin, which was present in nearly all isolates of B. pertussis bacteria in the U.S. through 2010, is now missing from more than half of the isolates.

"These findings tell us that there is an evolutionary advantage to lacking the protein that may have important vaccine implications," Lucia Pawloski, the first author of the study, said.

Researchers from the U.S. Centers for Disease Control and Prevention identified DNA insertions into the pertactin gene from 1,300 isolates that would prevent the expression of the gene. The first such isolate occurred in 1994. The next isolate was found in a 2010 sample. There were 267 isolates in total that were found without the expression of the pertactin gene, most of which were from samples obtained between 2010 and 2012.

The authors said the vaccine remains effective thanks to the other antigens in the vaccine, but they said public health authorities should not be complacent.

"This recent and drastic change in response to a particular vaccine antigen highlights the need to continue monitoring the circulating bacterial population to allow us to better predict future potential vaccine antigens and respond to the recent upsurge in pertussis," Pawloski said.

After less than 8,000 U.S. cases of pertussis were reported in 2000, there were more than 48,000 cases reported in 2012. The increase in cases may be due to improved awareness of the disease among doctors and the general public, more specific and sensitive diagnostics and waning immunity from the current acellular vaccine.