A groundbreaking study has shaken long-held beliefs about how poliovirus spreads, offering new insights into its transmission. Researchers, including T. Jacob John from Christian Medical College, Vellore, (now retired), Dhanya Dharmapalan from Apollo Hospitals, Navi Mumbai, Robert Steinglass, and Norbert Hirschhorn, have revisited the way wild and vaccine-derived polioviruses are transmitted. Their findings, published in Infectious Diseases, show that poliovirus spreads mainly through the respiratory route, contradicting the commonly accepted idea that it is passed through faecally contaminated food and water.
According to Dr. T Jacob John, the global campaign to eradicate polio has focused on the idea that the virus spreads through the faecal-oral route, with virus in food and water that have been contaminated by sewage. . However, he argues that evidence clearly points to respiratoy transmission as the main way the virus moves from person to person. This focus on contaminated food and water, he adds, may have been due to the prevalence of polio only in low income countries where sanitation/hgiene is poor, overlooking other key factors, such as high birth rates, the crowded living conditions and the way adults and older children socially interact with infants.
Throughout their research, the team carefully examined historical data and conducted a thorough analysis of how the virus spreads in communities. Their findings indicate that focusing on the wrong transmission route has delayed polio eradication efforts. “We found no evidence for transmission through contaminated food or water from available studies and observations, but all available information supports the respiratory route,” Dr. John explained. He also noted that this misunderstanding has led to the belief that the live oral polio vaccine (OPV) was essential to interrupt transmission of wild and vaccine-derived polioviruses. That explains why the eradication programme had been failing to fully stop transmission in many countries. In those countries, the vaccine efficacy of OPV is unacceptably low. In contrast, the inactivated polio vaccine has proven much more effective, particularly since the virus spreads primarily through the repiratory route. The vaccine efficacy of inactivated poliovirus vaccine (IPV) is excellent in those countries, just as in others where polioviruses were eliminated using IPV.
Dr. John also looked closely at past studies that linked polio to poor sanitation and water quality. While giving the OPV to children can build their immunity, through infection through the oral route, he pointed out that this does not reflect how the virus naturally spreads. Children who receive the OPV rarely pass the virus on to others, which raises questions about whether the virus actually enters the body through contaminated food or water. “Sabin’s challenge to prove or disprove respiratory transmission remained unresolved, till now” Dr. John remarked, referring to the scientist who developed OPV, who had called for more research into whether poliovirus spreads through inhaling oral droplets.
The study strongly supports the transmission route as respiratory, which fits better with the available data. Dr. John emphasized that the continued reliance on the OPV has led to outbreaks of mutated vaccine strains, which can cause polio sporadically and in outbreaks. These outbreaks are particularly common in areas where OPV is used, creating further obstacles to eliminating the disease. Periodically the vaccine-derived virulent mutant viruses get exported to polio-free countries, making matters worse.
One of the most important findings of the research was the role of re-infections in immune individuals, which plays a crucial part in the virus continuing to spread. People who have been re-infected do not show any symptoms, but they can still pass the virus to others, especially in places where older people and infants are in close contact with one another. Dr. John argues that this silent transmission among people who have already been infected, and later re-infected, is a major reason why the virus continues to circulate, particularly in regions where vaccine coverage is uneven or vaccine efficacy is too low.
By identifying droplet/aerosol transmission as the main way poliovirus spreads, Dr. John suggests a clear path forward: switching from OPV to the IPV globally. Unlike the oral vaccine, the IPV does not infect and cannot spread between people, making it completely safe. “Only the inactivated vaccine can be used in the polio-eradicated world,” Dr. John noted, urging health authorities around the world to speed up the transition from the oral vaccine to the inactivated version in order to fully eliminate polio.
Dr. John summarized the findings, stating, “The transmission of virulent polioviruses, whether wild or vaccine-derived, is through the respiratory route, similar to other contagious childhood diseases like measles, rubella, and diphtheria.” This shift in understanding not only has major implications for vaccination strategies but also challenges long-standing public health policies that have focused on improving sanitation and water safety as one way to stop polio.
As the world continues to fight poliovirus, these findings could be crucial in shaping the next steps toward eradicating the disease once and for all. If global health organizations follow Dr. John’s recommendation to focus on respiratory transmission and switch to the inactivated vaccine, the long-awaited goal of a polio-free world could finally be within reach.
Journal Reference
John, T. J., Dharmapalan, D., Steinglass, R., & Hirschhorn, N. (2024). “The respiratory route of transmission of virulent polioviruses.” Infectious Diseases. DOI: https://doi.org/10.1080/23744235.2024.2392791
About the Authors
T Jacob John (MBBS, DCH, FRCP(Edin), PhD, DSc) was trained in Paediatrics in India and the UK and in Paediatric Infectious Diseases in the USA. Nearly his entire career was in the Christian Medical College, Vellore, India, where he established India’s first Diagnostic Virology Laboratory in 1967. In 1978 the Laboratory was named the National Centre of Excellence by the Indian Council of Medical Research (Ministry of Health, Government of India).
He popularised paediatric immunisations in India from 1967 (seven years before WHO EPI was launched) and is popularly called ‘Father of Immunisation’ in India. He was elected President of the Indian Association of Medical Microbiologists (1984) and as President of the Indian Academy of Paediatrics (1999). He served on the Rotary International’s PolioPlus Committee and Health-Hunger-Humanity Committee during 1984-1992. In 1992 he was honoured by the Medical Council of India as the ‘Eminent Medical Man of the Year’ 1990. He retired from employment in 1995, and served as Emeritus Professor till 2000. He has published 670 scientific papers in Medical Journals.
Dhanya Dharmapalan (MD, FIAP, FPIDS) is a Senior Consultant in Paediatric Infectious Diseases at Apollo Hospitals, Navi Mumbai. She is the editor of nineteen pediatric textbooks and co-authored with TJ John the book “Polio: The Eradication Imbroglio. The Malady and its Remedy” (2021)
Robert Steinglass (MPH, The Johns Hopkins School of Hygiene and Public Health) has worked primarily for WHO and John Snow Inc., USA, for nearly 50 years in nearly 50 resource-poor countries, on strengthening immunisation programs, vaccine-preventable diseases control, and new vaccine introductions.
Norbert Hirschhorn (MD), co-founder of John Snow, Inc., USA, helped develop the oral rehydration treatment for diarrhea, from bedside to national programs. He was honored by the Dana and Pollin Foundations and Columbia University, and commended by USA President Clinton as an ‘American Health Hero.’
