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Acellular pertussis vaccines may prevent disease but not transmission

Acellular pertussis vaccines effectively prevent pertussis in vaccinated individuals, but may fail to prevent colonization and transmission to uninfected individuals, according to a study.

Acellular vaccines, which replaced whole-cell vaccines in the 1990s, may play a role in the recent resurgence of pertussis, some researches hypothesize.

To test this hypothesis, Tod J. Merkel and colleagues inoculated two groups of baboons – one with the whole-cell vaccine, the other with the acellular version – at ages 2, 4, and 6 months.

When challenged with active Bordetella pertussis bacteria at age 7 months, an unvaccinated control group of baboons contracted the disease, whereas neither vaccinated group developed pertussis symptoms.

However, the authors found that bacterial colonies persisted in both unvaccinated and acellular-vaccinated monkeys’ noses for up to 6 weeks. In contrast, whole-cell immunized baboons were bacteria-free within 3 weeks.

Further, the authors found that acellular-vaccinated baboons were able to pass the infection on to their uninfected cagemates.

The authors suggest that the difference in vaccine efficacy may be due to different immune responses, with the whole-cell vaccine spurring a response more similar to that produced by the live bacterium, compared with the acellular vaccine.

Combating pertussis will require a vaccine that prevents colonization and transmission to protect sensitive members of the population and achieve herd immunity. ( Xagena )

Source: PNAS, 2013