Virus World

Prophylactic vaccination is the most effective intervention to protect against infectious diseases. The commonly accepted paradigm is that immunization with both attenuated virus (live but with substantially reduced virulence) and inactivated (killed virus particles) vaccines induces adaptive and generally long-term and specific immunity in the form of neutralizing antibodies and/or activating pathogen-specific cellular immune responses. However, an increasing body of evidence suggests that live attenuated vaccines can also induce broader protection against unrelated pathogens likely by inducing interferon and other innate immunity mechanisms that are yet to be identified. The stimulation of innate immunity by live attenuated vaccines in general, and oral poliovirus vaccine (OPV) in particular, could provide temporary protection against coronavirus disease 2019 (COVID-19).

OPV was developed by Albert Sabin in the 1950s and consists of live attenuated polioviruses of the three serotypes. Early clinical studies showed that besides protecting against poliomyelitis, OPV reduced the number of other viruses that could be isolated from immunized children, compared with placebo recipients. Additional evidence of nonspecific effects of OPV came from the 1959 poliomyelitis outbreak in Singapore caused by type 1 poliovirus that was successfully stopped by the use of monovalent OPV that contained only type 2 poliovirus (1). Monovalent OPVs do not induce cross-neutralizing antibodies that target other virus serotypes, so the most plausible explanation was viral interference, which presumably is mediated by innate immunity.

Large-scale clinical studies of OPV for nonspecific prevention of diseases were carried out in the 1960s and 1970s. These involved more than 60,000 individuals and showed that OPV was effective against influenza virus infection, reducing morbidity 3.8-fold on average (2, 3). OPV vaccination also had a therapeutic effect on genital herpes simplex virus infections, accelerating healing. OPV not only demonstrated positive effects against viral infections but also had oncolytic properties, both by directly destroying tumor cells and by activating cellular immunity toward tumors (2). These observations were among the first examples of viral oncotherapy, which is being actively pursued.

Published in Science (June 12, 2020):

https://doi.org.10.1126/science.abc4262

Using two types of polio vaccines seems to provide stronger protection against the disease and may boost efforts to eradicate polio, a new study shows. The research involving nearly 1,000 children in India found that giving the Salk inactivated poliovirus vaccine (IPV) to those who had already been given the Sabin live-attenuated oral poliovirus vaccine (OPV) appeared to improve their immunity to the virus that causes polio. The findings, reported in the Aug. 22 issue of the journal Science, could prove crucial in eliminating the world's remaining pockets of polio in places such as Iraq and Syria.

"This study revolutionized our understanding of IPV and how to use it in the global eradication effort to ensure children receive the best and quickest protection possible from this disease," study senior author Dr. Bruce Aylward, assistant director-general for Polio, Emergencies and Country Collaboration at the World Health Organization, said in a journal news release. "IPV should be used to accelerate the eradication of the virus in populations that have limited access to vaccination," study author Dr. Hamid Jafari, WHO's director for polio operations and research, said in the news release. "The study has also provided the evidence for use of IPV among travelers to limit further international spread of the virus."

Since polio vaccine was developed in the 1950s, efforts to eradicate polio have relied mainly on OPV rather than IPV. However, these findings show that giving both vaccines to patients may be the best approach. "The global eradication effort is at a critical crossroad," Jafari said. "Endemic polio is increasingly geographically restricted to populations in insecure and inaccessible areas. Yet the virus in these areas persists with incredible tenacity and threatens the increasingly vulnerable populations in polio-free countries with weak or conflict-affected health systems."