Pertussis vaccine and transmission
http://www.ima.org.il/imaj/ar06may-2.pdf
Pertussis is considered an endemic disease, characterized by an epidemic every 2–5 years. This rate of exacerbations has not changed, even after the introduction of mass vaccination – a fact that indicates the efficacy of the vaccine in preventing the disease but not the transmission of the causative agent (B. pertussis) within the population [19].
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http://www.cdc.gov/ncidod/eid/vol6no5/pdf/srugo.pdf
The effects of whole-cell pertussis vaccine wane after 5 to 10 years, and infection in a vaccinated person causes nonspecific symptoms (3-7). Vaccinated adolescents and adults may serve as reservoirs for silent infection and become potential transmitters to unprotected infants (3-11). The whole-cell vaccine for pertussis is protective only against clinical disease, not against infection (15-17). Therefore, even young, recently vaccinated children may serve as reservoirs and potential transmitters of infection.
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http://www.pnas.org/content/111/2/787
Proceedings of the National Academy of Science
"Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model,"
The study concluded that infant baboons given Sanofi DTaP (Daptacel) vaccine at two, four, and six months of age were protected against developing outward clinical symptoms of pertussis after being exposed to B. pertussis at seven months of age, but they were still able colonize and transmit B. pertussis to other baboons.
The baboons that were vaccinated with whole cell pertussis (GlaxoSmithKline's Infanrix) also colonized B. pertussis upon exposure to B. pertussis, but they cleared the infection much faster than the acellular pertussis vaccinated baboons—in 18 days compared to 35 days.
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To quote NVIC's Barbara Loe Fisher:
"In my opinion, this study in infant baboons suggests that pertussis vaccine-acquired immunity has been an illusion. Although the vaccines may protect against severe B. pertussis clinical symptoms of the disease—such as paroxysmal coughing—they do not prevent colonization of B. pertussis bacteria and transmission of the infection to others.
In this study at least, recovery from previous B. pertussis infection was more effective in preventing colonization with B.pertussis upon direct challenge than either whole cell DPT (Infanrix) or acellular DTaP (Daptacel) and that suggests transmission of the infection to others after exposure to B pertussis would also be less likely when there is a history of naturally acquired immunity."
My comment:
Fisher might be a little bit hard to folow, but what she is saying is that after a baboon has been infected with the WC anti bodies, the B. pertussis bacteria is then found in the lining of the throat. In a human being, the throat would perhaps be irritated and perhaps sore, but most significantly this person can then infect others with whooping cough.
Now, the researchers did not say that DTaP vaccine causes vaccine strain pertussis infection. B. pertussis vaccines (both whole cell DPT and acellular DTaP/Tdap) are inactivated vaccines and do not cause vaccine strain infection the way some attenuated live virus vaccines can—such as live oral polio (OPV) and varicella zoster (chickenpox) vaccines.
However, the lead author Tod Merkel did comment to the New York Times that when exposed to B. pertussis after recently getting vaccinated, you could be an asymptomatic carrier and infect others, saying:
"When you're newly vaccinated, you are an asymptomatic carrier, which is good for you, but not for the population."