Two novel type-2 oral poliovirus vaccine (nOPV2) candidates are safe and immunogenic in young children and infants, according to new findings. "Based on the results from these phase-2 clinical trials, nOPV2 has received an Emergency Use Listing (EUL) recommendation from the World Health Organization (WHO), making it the first vaccine ever to go through this pathway that is meant for global-health emergencies such as polio," Dr. Ricardo Ruttimann of Fighting Infectious Diseases in Emerging Countries (FIDEC), in Miami, told Reuters Health by email. FIDEC is a non-profit that supports programs to control and prevent infectious disease in emerging countries, and is primarily funded by the Bill and Melinda Gates Foundation. While the world had come close to eradicating polio, paralytic disease caused by vaccine-derived polioviruses is on the rise, with 739 cases in 2020 as of December 3, Dr. Ruttimann and his team note. The WHO declared outbreaks due to type-2 circulating vaccine-derived poliovirus to be a Public Health Emergency of International Concern in 2014. Routine use of the type-2 component from the OPV was ended in May 2016, and more and more pediatric patients are being treated with injected inactivated poliovaccines against type-2 poliovirus, which are less effective for promoting intestinal mucosal immunity, the authors note. "The Global Polio Eradication Initiative (GPEI) supported the development of more genetically stable type-2 polioviruses for a vaccine," Dr. Ruttimann explained. "The new oral vaccine candidates (nOPV2-c1 and nOPV2-c2) are a modified version of the existing type-2 monovalent OPV (mOPV2) which is extremely safe and effective against polio, and it has been used for over 50 years. The nOPV2 vaccines contains the live, weakened virus, but it has been modified to make it more genetically stable than the existing mOPV2 and therefore less likely to revert to a form which can cause paralysis." The new report is on two single-center, multisite randomized trials: a phase-4 study using mOPV2 before it was withdrawn from routine use, and a phase-2 study of the two novel vaccines, including 150 children aged 1 to 4 years and 684 infants 18 to 22 weeks old. All participants in the phase-2 study received one dose of a novel vaccine, and some were given two doses 28 days apart. At baseline, the authors note, nearly all of the children were seroprotected. With each of the three vaccines, children were 100% seroprotected at 28 days. For infants, 94% were seroprotected at 28 days with mOPV2, 94% with high-dose novel OPV2-c1, 93% with low-dose novel OPV2-c1, 95% with high-dose novel OPV2-c2, and 91% with low-dose novel OPV2-c2. Both low- and high-dose novel OPV2-c1 and high-dose novel OPV2-c2 were non-inferior to the monovalent OPV2 vaccine. "The aim is to now use the vaccine for outbreak response for circulating vaccine-derived poliovirus (cVDPV) that are increasing across Africa as well as Afghanistan, Pakistan, the Philippines, Malaysia, and other countries," Dr. Ruttimann said. "Currently, outbreaks are being tackled using the original Sabin oral vaccine for type 2 polio (mOPV), which risks seeding further outbreaks in areas of persistently low immunisation coverage." He continued: "The nOPV2 candidate vaccine will be proceeding through Phase III trials with support from the GPEI. This study will take place in the coming months and it is required to achieve WHO Prequalification." "We are also planning additional studies of the nOPV2 coadministered with other vaccines used in expanded immunization programs," Dr. Ruttimann concluded. In another article in The Lancet, researchers in Belgium report on two clinical trials of nOPV2 in adults, which also found it was safe and effective. "The results from these two studies and the Emergency Use Listing represent exciting next steps for a world that already needed more OPV2 before the COVID-19 pandemic," Dr. Kimberly M. Thompson of Kid Risk Inc. in Orlando, Florida, writes in an editorial accompanying the study. "This progress will allow for broader use of novel OPV2 and the observation of evidence related to its actual performance in the field." —Anne Harding Source
