World marks switchover to bivalent oral polio vaccine

Between April 17 and May 1, 155 countries and territories around the world will stop using the trivalent oral polio vaccine and begin using a bivalent oral polio vaccine in what WHO has called the largest vaccine rollout in history.

Polio cases have decreased by more than 99.9% worldwide since 1988, and wild poliovirus exists in only two countries, Pakistan and Afghanistan, according to WHO.

The bivalent oral polio vaccine (OPV) protects against the two remaining wild polio strains, types 1 and 3. The outgoing trivalent OPV also protected against type 2 poliovirus, which has been eradicated in the wild but can still circulate as vaccine-derived polio.

The vaccine switchover is the first stage of a larger plan to withdraw all OPVs.

To mark the occasion, Infectious Disease News and Infectious Diseases in Children have compiled a list of five stories about OPV and polio eradication efforts.

OPV protects against infectious disease mortality

Oral polio vaccine given at birth to children in resource-limited countries is safe and also may be protective against other deadly infectious diseases, according to a recent study.

“Administration of oral polio vaccine-at-birth, particularly in the first days of life and in the absence of oral polio vaccine campaigns, may have a marked beneficial impact on infant survival,” Najaaraq Lund, MD, PhD, of the department of pediatrics at Kolding Hospital, Denmark, and colleagues wrote. Read more.

Infants infected with vaccine-derived polio in Myanmar

Two children have contracted circulating vaccine-derived poliovirus type 2 with accompanying acute flaccid paralysis in Myanmar, according to WHO.

“As a first step, withdrawal of the type 2 component from tOPV is planned for the last 2 weeks of April with a switch to bivalent, types 1 and 3 OPV, an unprecedented, global and synchronized effort,” Walter A. Orenstein, MD, an Infectious Diseases in Children Editorial Board member, and colleagues wrote in a perspective. “To induce some level of type 2 immunity in the population born after the switch, at least one dose of trivalent inactivated polio vaccine is now being recommended in the routine schedule — another extraordinary global effort.” Read more.

WHO seeks to reduce vaccine-derived polio cases with new vaccines

WHO aims to reduce cases of vaccine-derived polioviruses through the replacement of trivalent oral poliovirus vaccine with bivalent vaccine and the implementation of inactivated poliovirus vaccine, according to a recent report in MMWR.

“The global withdrawal of trivalent oral poliovirus vaccine, specifically its type 2 component, will represent a substantial milestone in the effort to eradicate polio, because it will mark the eradication of wild poliovirus type 2 and, in the long term, should lead to the elimination of type 2 vaccine-derived polioviruses,” Lee M. Hampton, MD, MSc, medical officer at the CDC, and colleagues wrote. Read more.

Detecting AFP clusters provides early warning on polio outbreaks

An early-warning system based on statistical modeling that maps occurrences of the most common symptom of polio could identify large outbreaks of the disease at an earlier stage and help limit their spread, researchers said.

Isobel M. Blake, PhD, a research fellow at Imperial College London, and colleagues said an algorithm based on identifying clusters of acute flaccid paralysis by location and time could have led to alarms being raised days — even weeks — before two recent polio outbreaks were officially confirmed. The algorithm, however, lagged behind for two other large outbreaks and for several smaller outbreaks, according to the researchers. Read more.

Eradication plan reduces poliovirus in Nigeria

The installation of several public health innovations has increased progress toward the eradication of poliovirus within Nigeria and its neighboring countries, according to a recent report.

“Nigeria was very close to interrupting transmission of polio and then experienced an upsurge of transmission,” researchers wrote. “Transmission in Nigeria has been driven by reservoirs in northern Nigeria, where several states are considered to be at very high risk.” Read more.