The US needs to prepare to introduce the novel oral polio vaccine

Polio in the US

For 40 years, the US, like much of the rest of the world, relied on an oral polio vaccine (OPV), which was routinely administered to children in the US until 1999.7 This vaccine is a weakened version of the virus, and stops people from getting infected, infecting others, and developing severe illness.8 It is also easier to administer than the inactivated version, which is injected. Through a combination of improved sanitation, which prevented people from passing infections to each other, and mass vaccination using the oral vaccine, the US managed to stop domestic transmission of wild polio in 1979.9 All of the Americas had done the same by 1994, and polio is close to eradication globally.10

In 2000, the US switched from using an OPV in its vaccine programme to only using an injected inactivated polio vaccine (IPV). The IPV produces antibodies that stop the virus from invading the nervous system, but it stimulates only limited immunity in the gastrointestinal system where people are first exposed to the virus.11 Consequently, it’s possible to be fully vaccinated and protected from the worst of polio, but to still “catch” the virus and spread it to others.

The US made this switch for two reasons. Firstly, when there is no endemic polio—as was the case in the US after wild polio was eradicated—the inactivated vaccine can give people the essential immunity they need to protect them against illness. Secondly, in very rare situations, the weakened virus in the oral vaccine can itself cause polio or mutate when passed between unvaccinated people into a strain that can cause paralysis.12 It was this strain of virus, which likely derived from the use of OPVs outside the US, that has been detected in New York.3

An uncertain strategy

Polio will continue to spread as long as there are people susceptible to infection and person-to-person transmission. So, now that the virus is circulating in New York, what should we do? State health officials are responding to the outbreak with a strategy that assumes inactivated vaccines combined with hygiene measures will eventually stop transmission.13 Yet we fear that this may not be enough. To end the cycle of infection, public health officials need to both protect people from paralysis and stop people from spreading the virus. Increasing the number of people who receive the IPV protects them from severe illness. But it will not stop the ongoing transmission of polio where it is already circulating, leaving people who are unvaccinated vulnerable. Statewide, 78% of children in New York have received three polio immunisations by the age of 2 years,14 but in some communities coverage is as low as 37%.3

With polioviruses now identified in 69 wastewater samples, we are concerned that public health officials cannot rely on hygiene to stop polio transmission in New York.15 In recent years, New York’s antiquated system for waste disposal has seen rubbish overflowing on the streets,16 and an aging water and sewage infrastructure has left some areas plagued by blocked sewers and unsafe drinking water.1718 Extreme weather events have also increased the frequency with which rainfall overwhelms New York’s sewage systems, exposing people to untreated wastewater.19 Inadequate public sanitation and safe water services increase the likelihood that there may be neighbourhoods in which people could be exposed to poliovirus from contaminated surfaces or water.20

Planning ahead

The reality on the ground has clearly changed since 2000. This is why New York needs to be prepared to introduce the nOPV. Inexpensive and easy to administer, the nOPV produces a gut reaction that protects the individual from disease and stops transmission using a more stable version of OPV, which is much less likely to mutate and cause paralysis.²¹ Unfortunately, the US is not yet prepared to administer nOPV, despite helping to finance its development.21 Ample global data show the safety and effectiveness of this new vaccine, with 450 million doses already administered in more than 20 countries around the world.22 Yet the vaccine has not even been approved for use in the US.23

The US should begin this approval process immediately and devise a strategy to define the triggers for using the nOPV—such as additional cases of severe disease or continuing detection in wastewater. Public health agencies should also start to devise how they would work with communities to explain the benefit of this type of polio vaccine. The US would also need to urgently invest in manufacturing scale-up so as not to cannibalise the existing and much needed global supply. A global stockpile of this vaccine is currently held by Unicef in Denmark, and while there may be enough vaccines to provide limited quantities to the US, any substantial draw would be at the direct expense of other countries with circulating polio. With proactive planning and investment, this risk can be managed.24

We cannot underestimate the threat of polio and the need to stop both disease and transmission. That means planning for the potential use of nOPVs.25 As we saw with covid-19 vaccines, where there is a will for rapid registration and the upscaling of production capacity, there is a way. While we may not need nOPV in the US today, we must be ready with it in the arsenal as a “plan B.”