Two Vaccines for One Polio-free World

Polio was once considered one of the most frightening diseases in the world until a team led by Dr. Jonas Salk developed the first successful polio vaccine. World Polio Day, held every October 24 to celebrate Salk’s birthday, is an opportunity for everyone working to eradicate polio to renew their commitment to creating a polio-free world for future generations. Today most of the world is polio-free, but the disease continues to disable children in some countries. And as long as polio exists anywhere, the disease remains a threat everywhere. There is no cure for polio, but there are two types of vaccines that protect against the disease: Salk’s vaccine, or inactivated polio vaccine (IPV), and Dr. Albert Sabin’s oral polio vaccine (OPV). Both 2015 and 2016 are major years for how we use these vaccines. As we observe World Polio Day, reflecting on history can help us understand the significance of these vaccines.

IPV was developed in 1952 at the University of Pittsburgh, and contains chemically killed wild poliovirus strains. This vaccine triggers an excellent immune response that protects against paralytic polio in the majority of people. IPV is much more expensive than OPV, requires trained healthcare workers and sterile equipment and procedures because it is an injectable vaccine, and is generally less effective than OPV in preventing the spread of poliovirus.

In 1963, OPV became available. OPV contains weakened strains of all three wild poliovirus types and largely replaced IPV for decades. OPV is administered orally and can be given by volunteers or minimally trained health care workers. Most countries use OPV as it has the unique ability to stop person-to-person spread of polio. Thanks in large part to extensive use of OPV, the number of polio cases has dropped more than 99% since the global polio eradication effort began in 1988. However, OPV’s effectiveness relies on the ability of its weakened strains to replicate in the human gut. In very rare instances, those weakened strains can replicate and change over long periods while circulating in communities with low vaccination coverage and eventually regain the ability to cause paralysis. These vaccine-derived polio cases are rare, and data shows their occurrence is declining. A large majority of the vaccine-derived cases, over 90%, are caused by a mutated form of the type 2 strain in OPV.

Based on the scientific evidence gathered over the years, both OPV and IPV are currently needed to end polio. The Polio Endgame Strategic Plan 2013-2018 requires all countries switch from OPV with 3 poliovirus types to OPV with 2 poliovirus types, which removes the type 2 strain from OPV. The type 2 strain in OPV is no longer needed as the type 2 wild poliovirus was certified as having been globally eradicated in September 2015. This switch from the 3-type OPV to the 2-type OPV is planned for April 2016. This will be one of the largest coordinated public health efforts in history since more than 156 countries still use OPV.

Countries not already using IPV have also been asked to start routinely using the vaccine in their national immunization programs to further reduce risk from removing the OPV type 2 strain. More than 40 countries have introduced IPV since 2013, and more are expected to do so in the coming months. Once global interruption of wild poliovirus occurs, OPV will be completely removed from vaccination programs around the world and IPV will become the only polio vaccine in use.

My colleagues at CDC and I have been working with countries and organizations like the World Health Organization and UNICEF to support the introduction of IPV and preparations for the global switch from 3-type to 2-type OPV in a variety of ways:

• Investigating problems specifically related to the timing of the switch and the introduction of IPV and identifying ways to address those problems.
• Putting what we learn to use by assisting countries with planning and training for the switch and the introduction of IPV.
• Helping to strengthen the inherent capabilities of national immunization programs, which is crucial since such programs are the ones that make sure children receive IPV, OPV, and other vaccines day after day.

I have been working with researchers in Albania, Sudan, The Gambia, Nepal, the Philippines, and South America to determine if health care providers and caregivers will accept children receiving an additional injection at the same visit as other vaccines as a result of IPV introduction. The project will help vaccination programs plan the best schedules for giving IPV and other vaccines to children, which will maximize the number of children who are fully protected from polio and other diseases.

Coming into contact with children around the world who benefit from vaccination is one of the best parts of my job as it helps inspire me and my team to work towards our goal of making the world polio-free for future generations.