Polio detected in US—in same NY county with explosive measles outbreak in 2019 [Updated]

 Health officials in New York have detected a case of polio, marking the first case of the dangerous viral disease in the United States in years.

The case was detected in a Rockland County, which in 2019 struggled with an explosive measles outbreak fueled by pockets of the community with low vaccination rates. Health officials in Rockland, neighboring New York City, and the state are now urging unvaccinated residents, particularly children, to get vaccinated, and those vaccinated, but at high risk, to get boosted.

“Many of you may be too young to remember polio, but when I was growing up, this disease struck fear in families, including my own,” Rockland County Executive Ed Day said in a statement. “The fact that it is still around decades after the vaccine was created shows you just how relentless it is. Do the right thing for your child and the greater good of your community and have your child vaccinated now.”

(Update, 6:33 pm ET: Details on the polio case are sparse for now, but officials in Rockland County said the case was in a young adult, who was unvaccinated and had not traveled outside the country recently. The person is no longer contagious, but the person did develop paralysis from their infection. It’s unclear how the person became infected and health officials are still investigating if others were exposed or infected.) According to the New York State Health Department a person was found to be infected by a vaccine-derived poliovirus type 2 (VDPV2), aka revertant polio Sabin type 2 virus. This is a similar type of poliovirus detected in sewage sampling in London in recent months.

Vaccine-derived polio strains stem from oral polio vaccines that use weakened (attenuated) polioviruses. These types of polio vaccines are no longer used in the US and many other high-income countries where polio is no longer a looming threat. Instead, the US and other countries use inactivated vaccines. The two vaccines have their own pros and cons.

How this happens

Oral polio vaccines are relatively cheap and highly effective at preventing paralytic polio. And, they also can prevent transmission. Because the vaccine contains a weakened virus that can still replicate in the intestines, they can generate strong immune responses in the gut that block wild poliovirus from replicating there in the event of a future infection. This means that in areas where wild polio is still a threat, the vaccine can prevent vaccinated people from being asymptomatic virus shedders.

The downside is that because the weakened vaccine virus can replicate in the gut, vaccinated people can shed the vaccine virus, which can spread if the conditions are right, mutate, and regain the ability to cause disease.

Here’s how that happens: Polioviruses are transmitted through oral-oral, or fecal-oral route, which means they spread because of poor hygiene—specifically unwashed hands after bathroom use and directly sharing saliva—or unsanitary conditions, such as if food and drinking water are contaminated with feces. In the event that an oral vaccine is used in a setting with poor hygiene or unsanitary conditions, plus low vaccination rates, the vaccine virus can spread from unvaccinated person to unvaccinated person, picking up mutations along with way, until it regains the ability to cause disease. At this point, it’s dubbed a VDPV.

In contrast, the inactivated vaccines use viruses that are not capable of replicating. Thus, they don’t run the risk of generating and spreading infectious viruses. But, they are more expensive—prohibitively more expensive for some countries—and they don’t produce strong immune responses in the gut, which could allow for wild poliovirus to replicate there and spread.

Finding a VDPD in the US suggests that the virus “may have originated in a location outside of the US where [oral polio vaccine] is administered, since revertant strains cannot emerge from inactivated vaccines,” used in the US, the New York State Department of Health said in a statement Thursday.

Polio risks

The health department went on to caution that polio is very contagious, and a person can spread the virus even if they have no symptoms. But, if they do have symptoms, they can feel flu-like, with fatigue, fever, headache, stiffness, muscle pain, and vomiting. These can appear up to 30 days after infection, during which time an infected individual can be shedding the virus to others.

As Ars has reported before, most people infected with poliovirus will have no symptoms, but about a quarter will develop those flu-like symptoms. In an estimated 1 to 5 in 1,000, the virus can attack the central nervous system, leading to more severe symptoms, including tingling in the legs and arms, meningitis, and paralysis. The Centers for Disease Control and Prevention estimates that about 1 in 200 people infected with poliovirus will develop paralysis. And about 2 percent to 10 percent of people with paralytic polio will die because the paralysis will affect their ability to breathe.

For anyone who survives an infection, however mild, an estimated 25 percent to 40 percent will develop post-polio syndrome, which can cause pain, weakness, and paralysis 15 to 40 years after the initial infection.

With the introduction of vaccines in 1955, the incidence of polio in the US has been cut down dramatically. The last case of polio originating in the US occurred in 1979. Travel and imported vaccine-related cases have popped up occasionally since then. The New York health department reports that the last time the CDC identified a VDPV in the US was in 2013.

Health officials in New York are now stressing vaccination and Rockland County is hosting a polio vaccination clinic starting  Friday, July 22.

“Vaccines have protected our health against old and new viruses for decades,” New York City Health Commissioner Ashwin Vasan said. “The fact is, the urgency of safe and effective vaccines has always been here, and we need New Yorkers to protect themselves against completely preventable viruses like polio.”