Poliovirus Detected in Europe: Should I Be Alarmed?

by Sophie Samiee and Mary Nell Wegner, EdM, MPH

As summer ends – along with the heat waves in Europe – you may be considering a trip across the Atlantic. Should news of polio in the wastewater be a deterrent? Here’s what to consider as you weigh whether to embark on this journey.

What is polio?

Polio, also known as poliomyelitis, is an infection caused by the virus poliovirus. There are three strains of poliovirus: Types 1, 2 and 3. Importantly, Types 2 and 3 were eradicated in 2015 and 2019, respectively. Type 1, however, remains endemic in two countries: Pakistan and Afghanistan.

Poliovirus mostly impacts children under five years old, and the Journal of the American Medical Association reports that although 70% of those infected have no symptoms, the symptoms that do occur can be life-threatening or cause permanent disability. This paper reports that 25% of symptomatic people have flu-like symptoms for two to five days, 1-5% get meningitis (inflammation around the brain and spinal cord) and 0.5% get weakness or paralysis.

Some patients, around 25-40% of cases, can develop post-polio syndrome 15 to 40 years after infection. Symptoms include muscle weakness, joint pain and mental and physical fatigue.

How is polio spread?

There are two ways that poliovirus is spread from person-to-person, regardless of whether a person shows symptoms:

• Poliovirus is present in the throat for one to two weeks after infection. During this time, saliva and respiratory droplets can spread the virus.

  
  

• Additionally, the virus is excreted in feces for three to six weeks. Those who are exposed to these feces, via contaminated food or water, can be exposed to the virus.

What vaccines are available?

Vaccines work by teaching the immune system how to respond when exposed to certain viral components. There are two poliovirus vaccines: inactivated polio vaccine (IPV) and oral polio vaccine (OPV).

The IPV was first licensed for use in the U.S. in 1955 and the OPV six years after. The IPV contains all three types of poliovirus, inactivated using formaldehyde, while the OPV contains live viruses that have been weakened by being grown in non-human cells.

Due to complications that can occur from the OPV, the IPV has been the only vaccine option available in the U.S. since 2000 and the CDC recommends infants and children get four doses of IPV between two months and six years old.

What are vaccine complications?

While the IPV and the OPV have similar effectiveness, the OPV carries some additional, seemingly paradoxical complications.

The IPV contains an inactivated virus, which means the virus cannot replicate or cause disease in the host. The OPV contains a weakened virus that also cannot harm the host unless it undergoes mutation.

After receiving the OPV, the harmless virus replicates in the throat and intestines in a manner similar to a wild infection and is shed in the feces for up to six weeks. People who are in close contact with the immunized person and get exposed to these viral particles in the feces can also reap the benefits of the OPV.

However, poliovirus is notoriously genetically unstable and likes to undergo spontaneous mutations. While many of these mutations are benign, some can cause the virus to regain its harmful characteristics and cause infection. The infection caused by vaccine, vaccine-associated paralytic polio, is symptomatically indistinguishable from wild polio.

The specific strain of OPV-derived virus that has become harmful is called vaccine-derived poliovirus and has the potential to spread in communities with low immunization rates. In fact, these vaccine-derived polioviruses are currently responsible for the majority of polio cases worldwide.

The potential for OPV mutation was the driving force of a global immunization change in 2016. Prior to this year, the OPV contained all three types of poliovirus. Because the Type 2 component in the vaccine caused over 90% of the cases of vaccine-derived poliovirus circulating in communities, the Global Polio Eradication Initiative completely removed Type 2 from the vaccine in 2016.

While the U.S. only uses IPV, many other countries still rely on OPV to manage polio. OPV is cheap and easy to administer since it doesn’t require needles and syringes. Since the chances of developing vaccine-associated paralytic polio is low and OPV stops transmission in communities with high immunization rates, the vaccine is still effective. The most dangerous scenarios are when a vaccine-derived poliovirus circulates in communities with low immunization rates.

How vaccinated is New Mexico?

Even if a country overall has high immunization rates, small pockets of populations with low immunization rates are at risk of polio outbreaks.

Prevalence of fully-immunized children in New Mexico has increased significantly since 2009 when coverage was under 50%. In 2021, 73% of children ages 19 to 35 months in New Mexico were up to date on their polio vaccine. Maintaining these high immunization rates is key to preventing polio outbreaks here in Santa Fe.

Am I protected from polio?

Whether you received the OPV prior to 2000 or the IPV thereafter, you are protected from polio. Both of these vaccines are effective at halting transmission of polio.

If you are not sure of your vaccination status, the CDC recommends you receive the complete vaccine series with IPV.

If you have an increased risk of exposure to the virus, like traveling to a polio-endemic country, working with viral samples or seeing patients who could be infected, then you should get a booster dose of IPV.

So, should I take that trip to Europe?

You are protected from polio regardless of which polio vaccine you received. Even if you are exposed to the wastewater containing poliovirus, your vaccinations will protect you.

There are strains of poliovirus – wild and vaccine-derived – that can be detected worldwide. As long as you are vaccinated, you are safe from infection.

The odds are in your favor that you will be fine. It’s good practice, however, whether in Santa Fe or in Europe (or anywhere else) to wash your hands, as well as fruits and vegetables, to minimize your potential exposure to viral particles.