Recent reports of polio virus detected in samples from a London sewage treatment plant have rightly raised major concerns among public health authorities and medical staff. The polio virus detected is the so-called vaccine-derived polio virus – this is not a “wild polio virus”.
There are currently two poliovirus vaccines: the oral poliovirus vaccine (OPV) and the inactivated poliovirus vaccine (IPV). The vaccine-derived poliovirus has been linked to the use of the OPV as this vaccine uses an attenuated poliovirus to produce an immune response.
The attenuated polio virus can still infect humans 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 polio virus can turn into a more dangerous strain of the virus that can cause illness.
In areas with high vaccination levels, the community is protected and the spread of the more dangerous virus is stopped. But in areas with lower vaccination coverage, unvaccinated people can be exposed to poliovirus that originated as a weakened vaccine strain but is now a more dangerous version. This virus is called a vaccine-derived polio virus.
As global vaccine initiatives have led to the near eradication of poliovirus, the number of vaccine-derived poliovirus cases has overtaken the number of wild-type poliovirus infections. In 2021, there were 697 new cases of poliovirus from the vaccine, compared to just six cases of wild-type poliovirus worldwide.
Vaccination with IPV does not immunize people with an infectious virus. Instead, it uses polio virus that has been chemically inactivated. This means that the virus cannot infect humans, eliminating the risk of vaccine-derived poliovirus. This vaccine is considered very safe. For this reason, many countries have moved away from using OPV and adopted IPV.
The UK switched from using OPV to IPV in 2004. However, OPV remains an incredibly effective vaccine that has played a major role in bringing about the near eradication of the polio virus and continues to be widely used around the world.
While there is no risk of vaccine-derived poliovirus infection from using the IPV, making IPV does pose a potential biological risk. To make IPV, large amounts of infectious poliovirus must be produced and then inactivated. This large-scale production of poliovirus has inherent risks and any violation of the biocontainment in a population with a low vaccination coverage could have serious consequences, as the poliovirus could be reintroduced.
Safer vaccine made from yeast
Vaccination strategies with OPV or IPV therefore carry a certain risk. In either case, the risk is surprisingly low. However, scientists have been looking for new and safer methods of vaccination against poliovirus for some time now. A possible candidate for a new poliovirus vaccine is the use of virus-like particles (VLPs).
VLPs are made up of the proteins that make up the virus’ outer shell, called a capsid. This allows the immune system to respond to this empty shell and trigger a protective immune memory response, so 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 kills the virus. controls and eliminates.
Because VLPs contain no genetic material from the virus, they are safe to manufacture and use without the risk of spreading the actual 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 ability to produce VLPs in production systems such as yeast. At the University of Leeds, we demonstrated that yeast can be made to produce poliovirus VLPs and then grown in large quantities.
The production system for these VLPs uses a similar infrastructure to other yeast-based production, such as beer brewing. This means that large quantities of VLPs can be produced quickly and safely in a very cost-effective manner.