How Effective Are Whooping Cough Vaccines?
Last year, Travis County reported 902 confirmed and probable cases of pertussis, also known as whooping cough. A majority of people who got the cough (80%) said they had been vaccinated against it. Whooping cough can be fatal for babies.
County and state health officials track the number of cases of pertussis/whooping cough. Those officials analyze trends in reported cases, but they don’t look in detail at what strains of the bacterium Bordatella pertussis are circulating.
Dr. Frits Mooi does. He is a researcher at the Netherlands Centre for Infectious Disease Control who studies a type of strain that is also found in the U.S. He says that strain began circulating around the early 90s. That’s about the time the current U.S. childhood DTaP vaccines started rolling out.
“What has happened is that this new strain, we call it the P3 strain, replaced the older strains and the new strain is more virulent than the older strains. Whether this strain is becoming even more virulent we don’t know, but we have evidence that the new strain is more virulent than the old strains which it has replaced,” Dr. Mooi told KUT.
P3 is short for strains of whooping cough that have a gene variant called ptxP3. Think of it as a light dimmer with a dial that you can turn for more or less light. Mooi says ptxP3 produces more pertussis toxin – the dimmer switch is up.
“And we think that is important because pertussis toxin is known to suppress our defenses against infection,” Mooi said.
Mooi expects this heightened toxin shortens the window of time in which a pertussis vaccine is effective. His research mainly focuses on the Netherlands and Europe. In the U.S., Mooi’s research is respected. It’s also controversial.
Epidemiologists at the U.S. Centers for Disease Control and Prevention argue Mooi’s hypothesis of a more virulent strain is unproven – in part because it’s based on studies in the lab. The CDC’s take is this: The only true way to know how vaccines are performing is to observe their effect on people who are getting them.
Jennifer Maynard is a fellow in chemical engineering at the University of Texas at Austin. She focuses her research on the pertussis bug. Maynard says a lot of scientists don’t think the bacteria evolve quickly enough to have changed significantly since the current vaccines were introduced.
“I think there may be different sub types of strains but I think that is still an open question and that is still controversial in the bordatella community. Are we vaccinating so much that the strains that are circulating and making people sick are now becoming stronger? I don’t know if we can actually say that,” Maynard said.
There is debate about how effective the whooping cough vaccines are. Maynard believes there probably is room for improvement.
“My read is that this vaccine is a good vaccine but it’s not great and that’s partly because it’s such a complicated bacteria that when the vaccine was being designed in the late 80s, we didn’t understand all of the components and everything that should go into a vaccine. So my feeling is that the vaccine is only providing short term immunity; it may not last as long as we’d like,” Maynard said.
Thomas Clark, a medical epidemiologist with the CDC, says no new vaccines are in the pipeline.
“It would be good to have vaccines that protect longer, that prevent transmission or that protect more completely while still being just as safe as the ones we have today, but there’s nothing really on the horizon,” Clark said.
Health officials say Central Texas appears to be on the downward end of an outbreak cycle, but cases are still cropping up this year.
Kim Frey lives in Georgetown. She almost lost her infant daughter to whooping cough. All five of her children got it, even though the four who were old enough to be vaccinated were. While Frey is skeptical about how effective the vaccines are, she still plans to use it.
“Who’s to say it wouldn’t have been worse without it you know? I definitely think there’s a place for vaccines and for my family that’s just the best decision because it’s how I feel like I’m protecting them the most,” Frey told KUT.
Public health officials agree. They say the best defense against whooping cough is getting vaccinated. The CDC says the results of a new study of 4-10 year-olds in California show the effectiveness of the childhood pertussis vaccines has not changed.
The Texas House has passed a bill to require hospitals and other providers to give newborn parents vaccination information about pertussis. Many Central Texas doctors already do this. The legislation is now in the Senate’s hands. You can read the bill here.
You can check out part one of KUT’s series on whooping cough in Central Texas here.