Polio was eradicated in the U.S. in 1979, just 24 years after the introduction of the first polio vaccine. After that, visitors periodically brought individual polio cases from other countries, but high U.S. vaccination rates and vigilant public health responses prevented outbreaks.
Something like that seemed to happen in New York state in June, although this case had an important twist. A young patient came down with paralytic polio. But his illness was part of a larger “silent” polio outbreak in which most people were asymptomatic. The outbreak was not caused by the “wild” version of the disease that used to disable an average of 34,000 Americans per year in the late 1940s, according to the Centers for Disease Control and Prevention. Ironically, a polio vaccine helped trigger this outbreak.
There are two types of polio vaccine: The one used in the U.S. operates with a “killed” virus; many other countries use a vaccine with a weakened “live” virus, which can cause disease in rare cases, says San Antonio infectious disease specialist Charles Lerner, MD. That’s not a threat to people who are vaccinated. But in largely unvaccinated populations – like the one where the New York outbreak took place – people are in danger.
“Presumably, this began with somebody who received live polio virus vaccine and then came to the United States and began infecting other [unvaccinated] people,” he said.
Since 2000, the U.S. has used the three-dose killed-virus vaccine in part because the live-virus vaccine poses a slightly higher risk, Dr. Lerner says. But other countries use the live virus vaccine because it only requires a single dose that’s swallowed.
“Giving a drop in a baby’s mouth is a lot simpler than three injections staggered over several months,” Dr. Lerner said.
While the risk of illness from the live virus vaccine must be taken seriously, it pales in comparison with the risk of not getting vaccinated for polio, Dr. Lerner says. New York would not have seen an outbreak if that region’s vaccination rates had been higher. Promoting vaccination is the only way physicians can prevent the horrors polio once routinely inflicted on young people.
“I’m old enough to have treated [polio patients] in artificial lungs,” Dr. Lerner said. “Imagine yourself encased in a tube with a tight collar around your neck and you can’t breathe. [The machine] breathes for you. … And that’s the rest of your life.”