Polio virus detected in children without symptoms: What does it really mean?

On May 9, 2025, health officials in Papua New Guinea reported to the World Health Organization (WHO) that they found a type of poliovirus called circulating vaccine-derived poliovirus type 2 ( cVDPV2 ) in stool samples from two healthy kids in Lae City, Morobe Province. These samples were part of a routine check after an earlier environmental sample from April 4 showed traces of the virus. The kids didn't show any symptoms, but the virus was present in their systems.

What is a vaccine-derived virus? The oral polio vaccine (OPV) contains a weakened version of the virus to help build immunity. In rare cases, especially in areas with low vaccination coverage, this weakened virus can circulate in the community and mutate over time. If it changes enough, it can cause illness just like the wild virus. That's what's referred to as vaccine-derived poliovirus.

Why is this a threat?
Even though the kids were healthy, the presence of cVDPV2 indicates that the virus is circulating in the community. This is concerning because Papua New Guinea has low vaccination rates, especially in certain provinces. For instance, in Morobe Province, the coverage for the third dose of the oral polio vaccine (OPV3) was just 44% in 2024. Low vaccination rates mean more people are susceptible to the virus, increasing the risk of an outbreak.

Poliovirus can cause a wide range of symptoms from nothing at all to very serious illness. About 70% of people infected with poliovirus don’t feel sick at all. They carry the virus but show no signs. Mild symptoms like fever, sore throat, headache, fatigue, nausea, stomach pain usually appear 3 to 7 days after exposure and go away on their own. In about 1 in 200 to 1 in 2,000 cases, the virus invades the nervous system, which can lead to Meningitis (inflammation of the brain and spinal cord lining), stiffness in the neck, back pain, and headaches and Paresthesia (pins and needles feeling in the legs or arms).

Even after recovery, some develop post-polio syndrome decades later, with muscle weakness, fatigue and joint pain.

About 70% of polio infections are completely asymptomatic. That means the person carries the virus and can spread it to others, but they don’t feel sick at all. Around 24% of infected people get mild symptoms.

This looks like the flu, fever, sore throat, fatigue, and maybe a headache or upset stomach. These cases usually go away in a few days and often go unnoticed.

Even if someone has no symptoms, they can still shed the virus in their stool and spread it—especially in places with poor sanitation or low vaccine coverage. So in short: Most people who get polio don’t know they have it—but they can still pass it on. That’s what makes surveillance and vaccination super important.