Polio vaccine

What Are Polio Vaccines?

Polio vaccines are the key to preventing a disease that once paralyzed millions of people worldwide. These vaccines come in two types: an inactivated poliovirus given by injection (IPV) and a weakened poliovirus given by mouth (OPV). While IPV is very safe, OPV can cause about 3 cases of vaccine-associated paralytic poliomyelitis per million doses. The vaccines have been incredibly effective, with reported cases dropping from 350,000 in 1988 to just 33 in 2018.

History and Development

The first successful demonstration of a polio vaccine was by Hilary Koprowski in 1950. However, it was Jonas Salk’s inactivated (killed) polio vaccine that gained widespread recognition in 1955. Albert Sabin developed the attenuated live oral polio vaccine in 1961, which became the vaccine of choice worldwide due to its longer-lasting immunity and ability to produce excellent immunity in the intestine.

Types of Polio Vaccines

Inactivated Polio Vaccine (IPV) provides protective antibodies after two doses, with at least 99% being immune after three. It is very safe and can be given during pregnancy or to those with HIV/AIDS. However, it does not provide the same level of intestinal immunity as OPV.

Oral Polio Vaccine (OPV) provides longer-lasting immunity but has a risk of causing vaccine-associated paralytic poliomyelitis in approximately one individual per 2.7 million doses administered. It can also circulate in under-vaccinated populations and revert to a neurovirulent form, leading to outbreaks.

New Developments

The emergence of circulating vaccine-derived poliovirus has led to the development of novel oral polio vaccine type 2 (nOPV2). This new vaccine is more genetically stable and less likely to revert to a virulent form. Genetically stabilized vaccines targeting poliovirus types 1 and 3 are also in development.

Global Efforts

The World Health Organization recommends full vaccination against polio for all children, with OPV given at birth followed by three doses of OPV starting at 6 weeks of age. At least one dose of IPV is recommended to ensure complete protection.

Until recent times, a trivalent OPV containing all three virus strains was used, but it was phased out in 2016 and replaced with bivalent vaccine containing just types 1 and 3. This switch led to outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2), which increased from 2 cases in 2016 to 1037 cases in 2020. A novel OPV2 vaccine was granted emergency licensing in 2021, offering greater genetic stability and reduced risk of reversion.

Challenges and Controversies

The development of polio vaccines faced significant challenges and controversies. In the 1930s, researchers like Kolmer and Brodie worked on live and inactivated virus vaccines, respectively. While both developed effective vaccines, their methods were scrutinized due to safety concerns.

Kolmer’s live vaccine was criticized for causing paralysis in some children, leading to its withdrawal. Meanwhile, Brodie’s inactivated vaccine faced skepticism about its efficacy until Salk’s successful trials in 1955 brought the world a safer and more effective polio vaccine.

Global Polio Eradication Initiative

A global effort to eradicate polio began in 1988, relying on the oral polio vaccine developed by Sabin. The Americas were declared polio-free in 1994, and Europe was declared free of polio in 2002. India was taken off the WHO list of polio-endemic countries in February 2012.

However, transmission of wild poliovirus continues to exist, with cases reported in Pakistan, Syria, Cameroon, and other countries. Resistance to vaccination programs has slowed down the eradication process, particularly in Pakistan and Afghanistan, where misconceptions about vaccine ingredients have led some parents to refuse vaccination.

Conclusion

The fight against polio is far from over. With continued efforts and advancements in vaccine technology, we can hope for a world free of this debilitating disease. The journey from the early experiments of Kolmer and Brodie to the current global eradication initiative has been fraught with challenges but also marked by significant progress. As we move forward, it’s crucial that we remain vigilant and committed to ensuring every child receives the protection they deserve.