What You Need to Know About Polio in the United States

The recent spate of polio-related news in the United States has left people wondering. Has polio returned? The short answer is yes, but the high-profile New York state outbreak is associated with unusual factors that don’t apply to the general public. Measures to address areas of dangerously low polio vaccination coverage around the United States could quell the epidemic and return the country to a poliovirus-free state.

Experts agree that the best defense against polio, the technical term for the disease caused by the poliovirus, is a vaccinated population. Fortunately, polio immunization rates in the United States have exceeded 90% in recent years, and most children receive her 3 doses by age 2, as recommended by the U.S. Centers for Disease Control and Prevention. .a Man from Rockland County, New Yorkis the only person in the United States to have polio in nearly a decade.

However, public health officials have since detected genetic signs of the virus in New York City wastewater samples, as well as in Rockland County and three other counties in the state, and others in the region. polio vaccination coverage hovered around 60% in three affected counties, leaving unvaccinated populations vulnerable. is placed in And many people who get the virus never develop symptoms, but they can pass the virus on to others.

To prevent the covert spread of polio in the community, New York Governor Kathy Hochul said: state of emergency declaration This month, pharmacists, paramedics and midwives were added to the list the state allows to administer the vaccine.

The type of poliovirus currently circulating in the United States complicates polio eradication here and reflects a history of vaccination against the condition. During the last decades of the 20th century, the United States relied on an oral polio vaccine containing an attenuated version of the virus. Oral vaccines are cost-effective, easy to administer, do not require needles, and induce an immune response that reduces the risk of later infection and prevents disease. It has additional benefits. A person with an attenuated virus can shed the virus for several weeks and infect unvaccinated close contacts without causing symptoms. This is a form of secondary immunity. This means that one simple vaccination can indirectly immunize many people against both infection and disease once immunity kicks in.

However, in sporadic cases, weakened viruses have led to polio in vaccinees.From 1980 to 1992, 109 cases of this vaccine-associated polio It occurred in 262 million doses of oral vaccine in the United States, with an average of about 8.4 cases per year. In response, and in an effort to eradicate wild polio from the country, in 2000 the United States used dead viruses and switched to injectable vaccines that do not carry this risk. It protects itself, but does not prevent viral infections.

In parts of the world where oral vaccines are still in use, attenuated virus circulates beyond secondary vaccination of people in direct contact and into unvaccinated or poorly vaccinated populations. may pass through. As it does so, it accumulates mutations and can eventually emerge as a disease-causing form known as vaccine-derived poliovirus. , prone to developing paralytic diseases, What happened in the Rockland IncidentVaccine-derived poliovirus can occur in the United States if travelers pick it up elsewhere and bring it back to the United States. Vaccinated people remain protected from paralytic polio caused by the vaccine-derived or wild-type virus.

Two weeks ago, the United States announced the World Health Organization’s List of countries where vaccine-derived poliovirus is endemicOne polio case in Rockland County and the detection of vaccine-derived virus in wastewater earned it a place on the country’s roster.

For insights on the polio situation in New York and the rest of the United States, visit Scientific American I spoke with an infectious disease specialist. They provide important information about who is at risk, who may need boosters, why vaccination is the most important preventive measure against polio, and the difference between vaccine-derived and wild poliovirus. provided information.

The polio case in New York sounds significant, along with the detection of the virus in the area’s wastewater. Are people in the United States currently at risk of paralytic polio?

Not if you are vaccinated. “It’s an unfortunate event because it’s completely preventable,” said Yvonne Maldonado, a pediatric infectious disease physician and director of the Department of Pediatric Infectious Diseases at Stanford University School of Medicine.

Wild poliovirus causes polio unrelated to vaccination. According to the CDC, there have been no cases involving wild poliovirus in the United States since 1979. No cases associated with wild poliovirus in the country since 1993“We know it’s gone because we looked for it and didn’t find it,” Maldonado says.

Thanks to decades of successful vaccination campaigns, wild poliovirus cases fell from hundreds of thousands worldwide in 1988. Only 6 in 2021, according to WHO. Global eradication of polio was within reach, but the geopolitics of Afghanistan and Pakistan, where the virus still lingers in the wild, hinders this important public health goal. Both countries have reported 21 wild poliovirus cases so far in 2022.

many parents skipped taking the child to the pediatrician for routine checkups There are concerns about declining vaccination coverage in the first year or two of the COVID pandemic. New York’s state of emergency could help expand access to the polio vaccine and thus halt its decline, says Amesh Adalja, a senior researcher and infectious disease physician at the Johns Hopkins Center for Health Security. The declaration will raise public awareness and “enable a wider range of practices so that relevant health professionals can vaccinate individuals,” Adalja said.

For most people in the United States, the risk of contracting vaccine-derived poliovirus is low, even in New York. Traveling to the state is safe, Maldonado says. The poliovirus is transmitted primarily through the unintentional ingestion of faeces, so beyond full vaccination, “regular handwashing and regular hygiene really keep you safe,” she says.

Do risks vary with age?

People infected with the poliovirus after puberty tend to have worse symptoms than babies, Maldonado and Adalja say.of CDC Childhood Polio Vaccine Schedule Three doses should be given by the age of 18 months, and the final dose should be given by the time the child enters kindergarten.

How do I know if I have already been vaccinated?

Most people in the United States are vaccinated against polio, Maldonado said, but the country doesn’t have a national tracking system, so decades-old records can be hard to find. Concerned people should consult a doctor, she says.

As of 2016, 92.5% of children had received the recommended three doses of polio vaccine by 24 months of age. According to the CDCThis is the highest rate of any pediatric vaccine described.to 97% of US residents had antibodies to wild poliovirus, according to a CDC analysis of data collected in 2009 and 2010. At this rate, vaccine-derived poliovirus will hit the immune barrier in most of the country.

One exception is Rockland County, New York.Partly because of the active anti-vaccine movement in the community, the proportion 60.3% polio immunization coverage by age 2, the third lowest in the state. At that level, “you start to see what happens when people let go of their vaccine commitments,” says Maldonado. “We are victims of our success in this country because people think they don’t have to worry anymore.”

How effective is the polio vaccine?

People who have been vaccinated with a virucidal vaccine can catch the virus and pass it on to others, but they do not develop symptoms. Attenuated forms of vaccination elicit stronger immune responses than dead virus vaccines and reduce the risk of infection from subsequent virus exposure.both vaccines given on a similar schedule, and both are highly effective against symptomatic disease. For adults, her three consecutive doses of the virus-killing vaccine are 99-100 percent effective for him, and children also get her fourth dose, according to the CDC. According to Maldonado, the number of injections varies with age because children and adults have different immune responses.

How safe is the polio vaccine?

Vaccines containing injectable inactivated virus currently administered in the United States “have been in use for over 60 years and are incredibly safe,” says Maldonado. “The risk is reversible and the only risk factor I can think of is pain at the injection site.”

Do people who were vaccinated decades ago need a booster against polio?

“I don’t worry,” says Maldonado. “We have never seen [vaccinated] Older people who develop paralysis. It’s truly amazing how well vaccines protect against disease. ”

Some experts recommend giving New York residents who work in high-risk occupations (such as medical or sewer workers) a boost. “We usually only give additional boosters to people traveling to countries like Afghanistan and Yemen where the poliovirus may be endemic,” says Adaljah.

The CDC says adults at high risk of exposure to polio can receive one. Inactivated polio vaccine ‘lifetime’ boosterThe agency lists several countries Asia, Europe, Africa As a destination that guarantees boosters.

How can I find information about polio risk and vaccination levels in my area?

Some state health departments publish polio immunization rates by county. This may indicate a robust polio immunity wall in the area. Most local public health departments do not post information about polio cases.

New York continues to monitor wastewater samples for poliovirus. But local governments usually don’t.

“The solution is very simple: vaccinate people,” says Adalja. Where anti-vaccine activists have lowered vaccination rates, “it will also be where polio thrives,” he says. “After their success, only pestilence and disease will follow.”