In spring 2022, public health authorities in both the United States and Great Britain reported the discovery of vaccine-derived poliovirus in several environmental samples from their respective countries. In July, the New York State Department of Health informed the CDC that they had identified a case of polio caused by vaccine-derived poliovirus type 2 (VDPV2) in an unvaccinated individual residing in Rockland County. Since this initial discovery, authorities have discovered additional cases in adjacent counties. While that situation is under investigation, it also raises concerns about the prevalence of vaccine-derived polio and questions about what risk it may pose to the public.
What is Vaccine-Derived Polio?
Vaccine-derived poliovirus is a strain of polio related to the polio vaccine, more properly known as the oral polio vaccine or OPV. OVP uses a weakened strain of the polio virus to create immunity in those inoculated. Since the 1950s, OPV has been a safe and effective means of preventing polio from spreading. Due in part to the implementation of OPV, the United States hadn’t seen a case of polio since 2013.
The issues around OPV and vaccine-derived poliovirus stem from the ways in which some kinds of OPV are formulated and the nature of herd immunity. Some forms of OPV utilize weakened but still living strains of poliovirus. While in healthy individuals, this serves to foster immunity, in immune-compromised people or while circulating in under-immunized populations, the strains of polio used in OVP may revert to a more virulent and infectious form. These cases are rare, but as a safeguard against them, the United States switched from OPV to the exclusive use of inactivated poliovirus vaccine starting in 2000. Due to the prevalence of vaccination against polio across the US, the risk of infection or transmission remains extremely low.
How Vaccine-Derived Polio Spreads
Like active poliovirus, vaccine-derived poliovirus may be spread either person-to-person or environmentally. Common means of transmission include fecal-oral transmission or contaminated food or water. This means that polio is especially prone to spread in areas with poor hygiene, poor water quality, or low rates of vaccination.
Symptoms of polio, encompassing vaccine-derived polio, may include the following:
- Sore throat
- Back pain
- Neck pain
- Pain or stiffness in the arms or legs
- Muscle weakness or tenderness
These symptoms are common to many illnesses, and their appearance does not mean that an individual has been exposed to polio. Polio in the United States and the UK is limited at present and likely to remain that way.
What Comes Next?
Vaccination is the most important and effective step in protecting individuals and families from vaccine-derived polio and other forms of polio. The vaccines currently in use are nearly universally available in both the US and the UK. The nature and type of vaccine will depend on the age and health of the individual. Further steps to limit the spread of polio include practicing good personal hygiene, following safe food and water handling guidelines, and avoiding exposure to sewage and the like.
The odds of vaccine-derived poliovirus becoming widespread in either the United States or Great Britain are extremely low. This is partly due to food and water safety and vaccination prevalence in both countries. However, both polio and vaccine-derived polio remain an issue globally. Both the World Health Organization and the US Center for Disease Control are fully engaged in the worldwide fight against polio, with the goal of eradicating the disease altogether.