General Discussion
In reply to the discussion: Why would your un-vaccinated kids be a threat to my vaccinated kids? [View all]ND-Dem
(4,571 posts)The pertussis vaccine used until approximately 2000 was an inactivated version of the Bordetella pertussis bacterium. Incapable of causing infection, this whole-cell vaccine (wP) appeared as effective as a natural infection at boosting immunity to subsequent exposure. But in a few instances, the wP vaccine induced rare but severe side effects, such as convulsions and encephalopathy in children.
An acellular vaccine (aP) was introduced in 1991; this version uses specific bacterial antigens rather than the entire pathogen and imposes fewer and less severe side effects. By 2001, the wP vaccine was replaced by the aP version, and the former was completely removed from US markets. Tested only for its ability to generate robust antibody responses, recent epidemiological studies and animal research have suggested that the aP vaccine is less effective than the wP version when it comes to preventing disease transmission.
The acellular vaccine was tested in the U.S. at a time when we had pretty much eliminated pertussis, so the force of infectionthe pressure on the vaccine to performwas really limited, said Witt. However, he added, It was not without a good purpose that the [aP] vaccine was developed.
Last March, Witt and his colleagues published a study in Clinical Infectious Diseases comparing the vaccination histories of 900 patients affected in Californias 2010 pertussis outbreak. It was the first year we were seeing teenagers who had never received the whole-cell vaccine, he said.
The researchers compared populations of children who had received a first shot of wP and booster shots of aP to those who had received only aP or not been vaccinated at all. Witt said that the earliest cases from the 2010 outbreak, identified in Marin County, were in a family thats unvaccinated, in a town that has pretty high rates of personal belief exemptions.
The researchers were surprised to find that, although the risk to unvaccinated children was higher, the majority of whooping cough cases occurred in children who had received either form of the vaccine. They found that children who had received a single primary dose of wP, followed by booster aP inoculations, had an eight-fold lower risk of infection than children in the same age group who had received only the acellular vaccine. We were very surprised that vaccinated children were at as much risk as they were, said Witt. [There were concerns] that we had spurious data, because everyone trusted the vaccine and the antibody response.
But this year, in a January PNAS study, researchers from the US Food and Drug Administration (FDA) compared the effectiveness of the aP and wP vaccines in baboons. FDAs Tod Merkel and his colleagues found that the aP vaccine was effective at preventing severe disease symptoms, but baboons inoculated with this version could still be colonized by the pathogen and transmit disease to unvaccinated animals.
http://www.the-scientist.com/?articles.view/articleNo/41029/title/Persistent-Pertussis/