What to know about CDC’s new polio alert

By Katia Hetter, CNN

(CNN) — Although polio has been eliminated as an endemic disease in the United States, that isn’t true for other parts of the world.

The US Centers for Disease Control and Prevention issued a Level 2 travel notice on March 9 warning that poliovirus continues to circulate in multiple parts of the world and advising travelers to take enhanced precautions. The agency recommended that travelers to affected countries ensure they are fully vaccinated against polio before departure.

Despite its eradication in the United States, health officials say international travel can still pose a risk when the virus is circulating elsewhere. Because poliovirus spreads easily and can move across borders through infected travelers, maintaining high vaccination coverage remains essential.

What exactly is polio, and how does it spread? If the United States no longer has ongoing transmission, why are travel alerts still necessary? Which parts of the world are seeing poliovirus circulation now? Should travelers check their vaccination status before international trips? If someone is unsure whether they are fully protected, what should they do next?

I spoke with CNN wellness expert Dr. Leana Wen to find out. Wen is an emergency physician and adjunct associate professor at the George Washington University. She previously served as Baltimore’s health commissioner.

CNN: What is polio, and how is the virus transmitted?

Dr. Leana Wen: Polio, short for poliomyelitis, is a highly contagious viral disease caused by the poliovirus. The virus primarily spreads through what’s known as the fecal-oral route. That means microscopic particles from an infected person’s stool can contaminate surfaces, food or water and then enter another person’s body through the mouth. It also can spread through respiratory droplets when people are in close contact.

One challenge with polio is that people can spread the virus without realizing they are infected. Many individuals have few or no symptoms but can still transmit the virus to others.

CNN: What symptoms does polio cause, and how often does it lead to paralysis?

Wen: Most people infected with poliovirus do not develop noticeable symptoms. Roughly 3 out of 4 infections are asymptomatic, according to the CDC.

When symptoms do occur, they are often mild and can resemble other viral illnesses. People may experience fever, fatigue, headache, nausea, sore throat and muscle aches. These symptoms usually resolve within a few days.

In a smaller percentage of cases, the virus affects the nervous system. Paralytic polio occurs when the virus damages motor neurons that control muscles. This can lead to weakness or paralysis, most often affecting the legs. One in 200 infections lead to paralysis, according to the World Health Organization. Among those people paralyzed, 5% to 10% die when their breathing muscles stop functioning.

CNN: If the United States eliminated polio years ago, why are travelers still being warned about it now?

Wen: The United States eliminated continuous transmission of polio in 1979 thanks to widespread vaccination. However, eradication within a country does not eliminate risk when people travel to places where the virus is still circulating. When travelers visit those regions, they can become infected and bring the virus back with them. That’s why public health authorities emphasize vaccination before international travel to affected regions.

The risk for any individual traveler is generally low if they are fully vaccinated. But from a population health perspective, preventing importation is extremely important. Even a single imported case could lead to local spread in communities where vaccination coverage is low.

CNN: What countries are currently seeing poliovirus circulation, and what does the CDC travel alert advise?

Wen: Poliovirus has been detected in 30 countries, according to the CDC’s travel notice. In addition to countries in Africa, Asia and the Middle East, the list also encompasses some European countries, including Germany, the United Kingdom and Poland.

The CDC uses four levels of travel health notices. Level 1 means practice usual precautions. Level 2, which applies here, means take enhanced precautions. Level 3 advises travelers to reconsider nonessential travel, and Level 4 recommends avoiding travel altogether.

For the current Level 2 polio notice, the enhanced precaution is ensuring that you are fully vaccinated against polio before traveling. For most people, that means completing the routine childhood series of inactivated polio vaccine. Some people in especially high-risk situations may be recommended to receive another booster.

CNN: What is the current situation in the United States regarding polio cases or detection?

Wen: The United States does not have ongoing transmission of polio, but public health officials must remain vigilant.

Health officials identified a paralytic polio case in 2022 in an unvaccinated adult in New York. That case, the first of its kind in nearly a decade, was significant because it showed that poliovirus had been introduced into the community. Investigators later detected related virus in wastewater samples in several surrounding counties, indicating that additional infections had likely occurred without being recognized.

Since then, health departments have continued monitoring wastewater and vaccination coverage. These surveillance systems are designed to detect early signs of poliovirus, so that health officials can respond quickly if needed.

CNN: Who should check their vaccination status before traveling internationally?

Wen: Anyone planning international travel should confirm that they are up to date on recommended vaccines, including polio.

Adults who are unsure about their vaccination status should review their records or speak with their health care provider. If documentation cannot be found, it is generally safe to receive the vaccine again.

Travelers heading to regions where poliovirus is circulating should be particularly careful to confirm their protection. Travel clinics and primary care providers can help verify vaccination records and advise on what additional vaccinations may be needed.

CNN: Do adults who were vaccinated in childhood need a booster before traveling to areas where polio is circulating?

Wen: For adults who completed the standard childhood vaccination series, immunity is generally long-lasting. However, the CDC recommends that some adults traveling to areas with increased risk of polio receive a single lifetime booster dose of inactivated polio vaccine.

It’s important to note that this booster is not part of routine vaccination for the general population. This additional step is specifically recommended for people who may be exposed to the virus through travel or certain occupational settings, such as health care work. Individuals who are not at high risk for occupational exposure but especially concerned about polio could inquire about the booster shot with their primary care physician.

More broadly, the continued presence of polio in parts of the world highlights the importance of global vaccination efforts. Eradicating polio worldwide is the only way to ensure it does not return. Until that goal is achieved, maintaining high vaccination coverage, conducting careful surveillance and staying alert to travel-related risks remain critical tools for protecting public health.

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