The Oregon Health Authority is encouraging pregnant women and others in contact with infants to get vaccinated against whooping cough, or pertussis.
Pertussis is a bacterial infection that spreads easily through droplets when someone coughs or sneezes.
It’s tricky to treat because it is often confused with a common cold in its early stage, when it’s easiest to treat with antibiotics.
In later stages, some people have intense coughing fits that can cause them to vomit, struggle to breathe or fracture a rib.
FILE - This 2016 illustration provided by the Centers for Disease Control and Prevention, based on electron microscope imagery, depicts Bordetella pertussis bacteria, which cause whooping cough. (Meredith Newlove/CDC via AP)
Courtesy of CDC / AP
It was a major cause of infant illness and death before vaccines protecting against it were introduced in the 1940s.
Pertussis is an endemic bacterium: one that’s around all the time and periodically causes waves of illness not connected to any particular seasonal cycle.
Last year, Oregon — and much of the country — reported a rise in cases of pertussis.
Oregon has had 1,475 confirmed cases so far this year, the most reported by the state since 1950, according to OHA.
“It’s not just a rise. We have broken records that were last set in the 1950s,” said Howard Chiou, M.D., Ph.D., medical director for communicable diseases and immunizations at OHA’s Public Health Division, in a video produced by OHA.
But the story behind that apparent surge is not a simple one of a disease gaining a foothold as vaccine hesitancy undercuts parents’ willingness to get their kids the shot.
Instead, children’s vaccination rates have mostly held steady, and a bunch of factors likely explain the surge in cases reported in Oregon and nationwide, according to Chiou and epidemiologists from the U.S. Centers for Disease Control and Prevention.
The story starts with the shots themselves.
The original pertussis vaccines from the 1950s produced long-lasting immunity against infection, but carried a risk of serious side effects.
In the 1980s, the United States shifted to using shots that had less of the pertussis bacteria in them, known as acellular vaccines.
Following that shift, epidemiologists started to see a resurgence, often in school-aged children who had been vaccinated years earlier.
Their conclusion: immunity from the acellular vaccines doesn’t last as long.
“The new vaccine is much, much safer. It works just as well. But the duration of protection you get is much shorter,” Chiou said.
And then there’s the effect of the COVID-19 pandemic.
With masking and social distancing measures in place, reported pertussis cases in Oregon dropped to just a handful for several years.
That likely led to less passive immunity from recent infections in the population and contributed to the current rise in cases.
There’s also the likelihood that states are identifying cases that wouldn’t have been counted in past years.
In 2020, the CDC changed the way it defines and counts pertussis cases, a change its scientists estimated could explain a 10-25% increase in case counts.
And finally, in Oregon, vaccination rates for some key groups — like pregnant women — have fallen, according to Chiou.
The percentage of Oregon kindergarteners up to date on their pertussis boosters has also fallen below the national average.
“All these factors combine to explain this big surge we’re seeing,” Chiou said.
The CDC recommends that pregnant women receive a dose of T-Dap, a combination vaccine that protects against pertussis, tetanus and diphtheria, during every pregnancy, between weeks 27 and 36.
It’s a strategy to protect infants from birth to 2 months old, before they’re able to receive the shot themselves. Other caregivers, like fathers and grandparents, can also receive a booster dose to help protect a new baby.
Oregon has reported 87 cases of pertussis and 22 hospitalizations this year in children younger than 12 months, and one infant has died.
