Whooping cough cases are surging across the United States, with preliminary CDC data indicating a fivefold increase compared to the same period last year. This spike represents the highest number of infections since 2014, raising concerns about the effectiveness of current vaccination strategies. The FDA is now considering the use of human challenge trials to expedite the development of improved vaccines.
Pertussis Resurgence
The U.S. is experiencing a significant resurgence of pertussis, also known as whooping cough. According to the CDC's Nationally Notifiable Diseases Surveillance System, there have been 14,569 cases this year, compared to 2,844 at the same time last year. This increase marks a return to pre-pandemic levels, with cases trending upward even before the emergence of COVID-19. Dr. Susan Hariri of the CDC's National Center for Immunization and Respiratory Diseases noted the concerning trend, stating there is "no indication of slowing down."
Limitations of Current Vaccines
Despite high pertussis vaccination rates in the U.S., hovering around 90%, the upward trend in infections persists. Experts attribute this to the waning protection offered by current vaccines, which provide strong initial immunity that diminishes after two to three years. Dr. Archana Chatterjee, a pediatric disease specialist and member of the FDA's Vaccines and Related Biological Products Advisory Committee, stated, "We know that we do not have very good pertussis vaccines... These vaccines have done a yeoman's job for us for many decades, but they are not doing the job as well as they used to do."
The Rise of Mutated Strains
Adding to the challenge, there is evidence suggesting that the bacteria causing pertussis is evolving. Dr. Tod Merkel, associate director of research in the FDA's Office of Vaccines Research and Review, indicated that 90% of bacterial strains cultured in human infections in the United States now exhibit mutations that allow them to evade vaccine-induced immunity. This adaptation further reduces the effectiveness of existing vaccines, particularly in young children, where protection can wane within two to three years.
Exploring Human Challenge Trials
To accelerate the development of more durable and effective pertussis vaccines, the FDA is considering the use of human challenge trials. These trials involve intentionally infecting participants with pertussis under controlled conditions. While this approach could expedite vaccine testing, it also presents challenges. Researchers can assess a vaccine's ability to prevent mild early symptoms and bacterial colonization in nasal passages, but they cannot directly measure its impact on preventing severe disease, which is the primary goal of vaccination.
Mixed Reactions to Challenge Models
Labs in Canada and the UK presented their models for conducting pertussis challenge trials to the FDA advisory committee. While experts acknowledged the potential of this approach to speed up vaccine testing, concerns were raised about whether these studies have been sufficiently refined. Dr. Melinda Wharton, associate director for vaccine policy and clinical partnerships at the CDC's National Center for Immunization and Respiratory Diseases, expressed support for the concept but remained uncertain about its current readiness, stating, "I'm very supportive of this; whether or not we are quite there yet, I'm not totally sure."
