The poliovirus situation
What you need to know and please don't panic
Poliovirus is making the news, and I want to share a little context so hopefully you feel less worried, because right now polio is not an active threat to children, especially those who are vaccinated.
When individuals get infected with polio 90-95% are asymptomatic. In the remaining 5-10%, individuals have a minor illness that would look like any other minor illness - fever, headache, sore throat, nausea, vomiting and fatigue. In the 0.1% of cases where poliovirus leads to meningitis and damages the motor neurons in the spine, people can have severe pain and paralysis. This context matters because it explains how we could miss community spread of polio - paralysis is relatively rare and most individuals have an illness that would be mistaken for any other cold.
After a vaccination campaign that started in 1950s vaccination has been standard and mandated for children. Immunization against polio is touted as one of the world’s greatest achievements because we nearly eradicated it. The last outbreak of wild type / type 1 / OG polio was in 1978 in the US! Type 1 polio is eradicated everywhere except Pakistan and Afghanastan, but outbreaks happening more recently and broadly are derived from the oral polio vaccine and are referred to as type 2. We know less about type 2 overall, like whether it is less likely to cause paralysis than the type 1, but type 2 did originate with an oral polio vaccine.
Oral polio vaccines deserve a lot of credit - they were cheap and allowed for global mass-vaccination. The vaccine produced a lot of mucosal immunity because it was taken by mouth, and mucosal immunity is the best protection against a virus that is normally acquired in the nose/mouth/throat. The oral vaccine also was shed or spread by those who received it, resulting in boosting and protection of others in the community. However, a small number of individuals with the OPV get sick, because it’s a live virus that’s been attenuated or weakened. In rare cases, around 1 per million first doses of OPV (this estimate range is actually quite large with some estimates indicating it’s more or less common depending on the country), the vaccine recipient gets paralytic polio.
OPV hasn’t been used in the US for more than 20 years, but abroad it has been used though they stopped using OPV containing strain 2 back in 2016 because it seemed to be responsible for more vaccine associated paralytic polio than the other strains. The main barrier to internationally using IPV - the one we use in the US that’s not a live vaccine and doesn’t cause anyone to get paralytic disease - has been cost. This type 2 vaccine strain has been circulating internationally in communities where there are low vaccine rates, likely mostly internationally and has developed more and more “neurovirulent” traits making it more like the original polio.
1 case of paralytic polio was seen in Rockland, NY leading to analysis of wastewater and finding evidence of community spread in NYC and Rockland over the past few months. Statewide 22% of children are unvaccinated and in NYC around 15% are unvaccinated. These children are the ones most at risk.
So what do I do?
In the US we give IPV to all infants at 2, 4, 6 months of age as well as a booster dose between 4-6 years of age. This seems to provide excellent protection even against this type 2 strain. So if your children are vaccinated, you should not worry.
If your children live outside of Rockland County and NYC it is exceedingly unlikely they will encounter polio.
If you live in this area and your children are not yet vaccinated, staying away from sick people and surrounding your children with vaccinated individuals (adults, children, caregivers who are vaccinated) should protect them. Even if there are 100s of cases of type 2 polio circulating this is in a population of 10 million and over a course of 3 months, so you are still very unlikely to encounter polio. Even if you do, remember that 90-95% are asymptomatic and it’s very few who develop neurologic symptoms.
For the adults in your home born after 1955 in the US, it’s safe to assume you were vaccinated as children and you’re protected. If you were born abroad, had limited or restricted medical care as a child, and are not confident in your vaccine status, you could always get 1 IPV booster. This is being offered in Rockland county by the public health department and are likely accessible from primary care doctors at Federally Qualified Health Centers.
London has a similar outbreak and decided to boost every child with an extra dose of IPV. The idea behind this strategy is that this vaccine campaign will capture the children with 0 vaccines who are most at risk and also may drive up community protection against asymptomatic, mild spread.
When we think of what protection is adequate against polio, it very much depends on the volume of polio in the environment. If you are 90% protected against something less than 1 in a million, it’s enough. If you are 99% protected against something that’s 1/100 it feels less acceptable.
If community spread continues or grows in the US, we could be in a different situation where extra doses are recommended similar to London, but we’re not there yet.
It’s a disappointing set back in the global fight against polio to see this happening as it’s mostly preventable. The OPV strains would not have had an opportunity to mutate and develop “neurovirulent” characteristics if everyone was vaccinated.
But if you’ve done your part and vaccinated your family, I wouldn’t worry.
Please drop any questions in the comments!
References / Further reading:
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