we are developing a safer vaccine that does not use any genetic material from the virus
Recent reports of poliovirus being detected in samples from a sewage treatment plant in London have rightly caused great concern among public health agencies and medical staff. The poliovirus detected is called vaccine-derived poliovirus – it is not “wild poliovirus”.
There are currently two polio vaccines available: oral polio vaccine (OPV) and inactivated polio vaccine (IPV). Vaccine-derived poliovirus is linked to the use of OPV because this vaccine uses weakened poliovirus to produce an immune response.
Weakened poliovirus can still infect people and be shed by the vaccinated person. This can cause the weakened virus to spread from person to person. And in rare cases, this weakened poliovirus can transform into a more dangerous strain of the virus that can cause disease.
In areas where vaccination levels are high, the community is protected and the spread of the most dangerous virus is stopped. But in areas with lower vaccination rates, unvaccinated people can be exposed to poliovirus which was originally a weakened vaccine strain but is now a more dangerous version. This virus is called vaccine-derived poliovirus.
As global immunization initiatives have resulted in the virtual eradication of poliovirus, the number of vaccine-derived poliovirus cases has exceeded the number of wild-type poliovirus infections. In 2021, there were 697 new cases of vaccine-derived poliovirus compared to just six cases of wild-type poliovirus globally.
IPV vaccination does not immunize people with an infectious virus. Instead, it uses poliovirus that has been chemically inactivated. This means the virus is unable to infect people, eliminating the risk of vaccine-derived poliovirus. This vaccine is considered very safe. For this reason, many countries have abandoned the use of OPV and adopted IPV.
The UK switched from OPV to IPV in 2004. However, OPV remains an incredibly effective vaccine that has helped to nearly eradicate poliovirus and remains widely used around the world.
Although there is no risk of vaccine-derived poliovirus infection when using IPV, the manufacture of IPV carries a potential risk of biohazard. To make IPV, large volumes of infectious poliovirus must be produced and then inactivated. This large-scale production of poliovirus carries inherent risks and any violation of biocontainment in a population with low vaccination coverage can have serious consequences as poliovirus could be reintroduced.
A safer yeast vaccine
Vaccination strategies with OPV or IPV therefore involve a certain level of risk. In either case, the risk is surprisingly low. However, for some time now, scientists have been working to develop new, safer methods of vaccination against poliovirus. A potential candidate for a new polio vaccine is the use of virus-like particles (VLPs).
VLPs are assembled from the proteins that make up the outer envelope of the virus, called the capsid. This allows the immune system to react to this empty shell and triggers a protective immune memory response, so that the next time the immune system is exposed to a viral capsid (as in the case of a viral infection), it can generate an effective response that quickly controls and eliminates the virus.
Because VLPs do not contain genetic material from the virus, they can be made and used safely without the risk of spreading disease. This method has already been used very effectively to produce the human papillomavirus vaccine.
Another advantage of using VLP vaccines for a disease such as poliovirus is the potential for VLP production in production systems such as yeast. At the University of Leeds, we have shown that yeast can be induced to produce poliovirus VLPs and then cultured in large quantities.
The production system for these VLPs uses a similar infrastructure to other yeast-based manufacturing, such as beer brewing. This means that large quantities of VLPs can be produced quickly and safely in a very cost effective manner.