A male immunodeficient patient excreted strains of a vaccine-derived poliovirus for 28 years, a study has found. This case suggests that there are new barriers to polio eradication, according to Glynis Dunn and coauthors of a research article published August 27 in PLoS Pathogens.

Poliovirus strains in the oral polio vaccine (OPV) can be transmitted from person to person in populations with low immunity and can cause outbreaks. The strains can also replicate for long periods of time in an immunodeficient individual. The patient in question received childhood OPV immunizations at 5, 7, and 12 months of age and a booster when he was about 7 years old. His case is the longest-known example of a vaccinated patient excreting the live poliovirus.

The researchers analyzed 185 stool samples that the patient provided between 1995 and 2015. All stools were positive for strain 2 polio virus; the virus titres shed in the stools were “comparable to virus titres shed by healthy vaccinees and paralytics cases infected with vaccine or wild poliovirus.”

The excreted virus began to diverge from the vaccine strain around the time of the individual’s last known OPV vaccination, acquiring various mutations that affected its antigenic structure.

The patient excreted “a highly virulent and antigenically modified type 2 poliovirus at high titres for a period estimated to be 28 years so far … Provided antibody titres and immunizations coverage are maintained, it is likely that the population will be protected against paralytic disease, but it is also possible that this virus could circulate in populations only using [inactivated polio vaccine] as described in Israel for wild poliovirus, thus representing a possible source of polio reemergence,” according to the authors.

Read the full article in PLoS Pathogens ( doi:10.1371/journal.ppat.1005114 ).