CNN —
The number of whooping cough cases in the United States is skyrocketing, up fivefold from the same period last year, according to preliminary data released Friday by the Centers for Disease Control and Prevention (CDC).
That’s the highest number of whooping cough cases since 2014 and “shows no signs of abating,” said Dr. Susan Hariri of the CDC’s National Center for Immunization and Respiratory Diseases, who presented the data Friday at a meeting of experts who advise the Food and Drug Administration on vaccine decisions.
The surge in cases this year suggests the disease, also known as whooping cough, is back to pre-pandemic levels.
Even before the COVID-19 pandemic, pertussis cases had been on the rise in the United States because the current vaccine provides strong protection early on, but its effectiveness fades after two to three years.
“We know that the whooping cough vaccine is not very good,” Dr. Archana Chatterjee, a pediatric disease specialist and dean at the University of Chicago Medicine, said at the conference.
“These vaccines have done a great job for us for decades, but they’re not as effective as they once were,” said Chatterjee, who serves on the FDA’s Vaccines and Related Biological Products Advisory Committee.
On Friday, the committee met to discuss whether it’s time to allow pharmaceutical companies to intentionally induce whooping cough in people — so-called human challenge trials — as a key test for vaccines.
As with many infectious diseases, pertussis cases fell to unusually low levels during the pandemic as people limited social interactions and took other precautions to protect themselves from COVID-19.
In 2020, there were about 6,000 cases of whooping cough in the United States, but that number has dropped further in 2021 to about 2,000 cases. In 2022, there were about 3,000 cases, and last year there were about 5,000 cases.
There have been 14,569 confirmed cases in the United States this year, up from 2,844 during the same period last year, according to the CDC’s National Notifiable Disease Surveillance System.
Whooping cough begins with symptoms similar to those of the common cold: runny nose, sneezing, slight fever, and a tickly cough. After 1-2 weeks, the infection progresses to a new stage, causing severe coughing that spreads throughout the body.
These coughing fits can become severe enough to cause patients to vomit or break ribs, and they often make a wheezing noise as they try to breathe. Antibiotics can treat the infection, but only if it is caught within a few weeks before the debilitating, painful cough begins. After that, the only treatment is palliative care with plenty of rest and fluids until the infection subsides.
Unvaccinated infants and adults are at greatest risk of severe infection and, in rare cases, death, but doctors are increasingly seeing infections in vaccinated people.
Children usually receive five doses of the whooping cough vaccine (called DTaP or Tdap, which also protects against tetanus and diphtheria) by the time they reach age 6. A booster shot is recommended for children at age 11 or 12. Pregnant women are also recommended to be vaccinated against the infection, and adults are given a booster shot every 10 years.
Hariri said the U.S. has high pertussis vaccination coverage, about 90%, and has not fallen during the pandemic as has happened in other countries.
Despite this, the number of infected people continues to rise.
The increase in cases is not fully understood, but there is evidence that it may be due to changes in the bacteria that causes the infection, Dr. Todd Merkel, associate director for research at the FDA’s Office of Vaccine Research and Review, said in a presentation to the committee on Friday.
In the 1990s, the United States changed the type of vaccine it used to prevent whooping cough, switching from a whole-cell vaccine that caused high fevers and other worrisome symptoms in children after being given to a newer vaccine that didn’t cause as many reactions but also offered less protection and lasted shorter.
Merkel said other countries that have switched to the new vaccine are also seeing rising infection numbers.
Experts believe that the incomplete protection offered by the new vaccines is allowing the infection to spread, and also causing the bacteria to mutate in order to evade the immune response generated by vaccinations.
Merkel said Friday that 90% of bacterial strains cultured in human infections in the United States are associated with mutations that evade vaccine protection.
For young children who are vaccinated against whooping cough, the protection fades rapidly after two to three years and may fade long before age 11, when a booster shot is recommended.
Infants are at highest risk of serious illness, but as protection wears off, infections are increasingly occurring among older children and teenagers.
As a result, the search began for a more effective and long-lasting pertussis vaccination with fewer side effects.
But testing new vaccines is difficult because whooping cough recurs in epidemics every three to five years, and researchers can’t predict when or where outbreaks will occur, so vaccine makers need lots of infected people to test their shots.
Enter human challenge studies.
In some ways, whooping cough is an ideal infection to test in a human model: It can be cured with antibiotics in its early stages, protecting research subjects from harm.
Most people experience minimal symptoms in the early stages, and while researchers can measure the vaccine’s ability to prevent mild early symptoms and to prevent the bacteria from establishing in the nasal passages, the pertussis challenge model cannot directly measure the extent to which the vaccine prevents severe disease, which is the goal of most vaccines.
The researchers also don’t know what immune factors indicate protection from whooping cough, so they can’t gauge whether the vaccine gives people the same or better protection as that offered by the approved vaccines. This strategy is called bridging.
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On Friday, labs in Canada and the UK released models for how to conduct pertussis challenge tests.
FDA advisers were then asked whether they believed these types of trials could measure the right things, and if so, whether they would provide enough evidence on which to base vaccine approval.
The laboratory model has received mixed reactions from experts: on the one hand, they said that this approach is exciting and will undoubtedly speed up the testing of new vaccines, while on the other hand, they were not sure whether these studies were well coordinated.
“I’m a big supporter of this, but I’m not entirely sure we’re there yet,” said Dr. Melinda Wharton, deputy director for vaccine policy and clinical partnerships at CDC’s National Center for Immunization and Respiratory Diseases.