Re-purposing vaccines for COVID-19: Need for context

The Sars-CoV-2 virus has befuddled scientists on two counts. First it is a novel virus, whose genetic structure was deduced only 6 months ago. Since then, a hunt for a cure or vaccine has been on. The virus is also evolving, with multiple strains in circulation. In an additional twist, Sars-CoV-2 seems to produce a spectrum of disease conditions – from asymptomatic, mild symptoms to severe, fatal disease. Co-morbid conditions like hypertension, diabetes, obesity have been co-related to higher mortality rates. Yet these are not universal and the specific conditions that drive the various disease manifestations remain largely unknown. Prospective drugs and vaccines are being trialled, but given the complexity of the disease both will take time to be developed.

While the world waits for a way to defeat Sars-CoV-2, several scientists have suggested repurposing existing drugs and vaccines. Recently, Dr Robert Gallo, co-founder and director of the Institute of Human Virology at the University of Maryland School of Medicine and co-founder of the Global Virus Network, recommended using the Sabin Polio Vaccine (OPV) as a stop gap vaccine for COVID-19. The unprecedented spread of this disease has enforced countries to take drastic measures, but what considerations should underlie the decision to use OPV?

The premise of a stop gap vaccine is that the polio vaccine elicits an emergency innate immune response that could offer protection against the coronavirus. OPV contains a live attenuated form of the polio virus, that upon entry into a human recipient will temporarily live and grow in the respiratory tract. This action of the virus stimulates a two phased immune response – a non-specific emergency innate response and a polio-specific antibody response. The antibody response contributes to long-term immunity specific to polio. But the non-specific emergency response lasts for a relatively short time and can fight against any invading virus. It is this response that scientists believe can boost the body’s immunity against Sars-CoV-2.

Essentially OPV is not to considered in the same manner as a traditional vaccine and will not confer protection against Sars-CoV-2 as it does against polio. The same effect could be achieved by any live, attenuated virus or even by a less dangerous viral infection that resides in the respiratory tract. OPV is the most recommended option because it is cheap, widely available and has been previously shown to improve immunity against flu. But will it work on Sars-CoV-2?

The use of any stop gap vaccine needs to be trialed for its efficiency in the target population. First the contribution of innate immunity in protecting against Sars-CoV-2 needs to be examined. Second, it is critical to investigate if a similar innate immune response is generated in those already vaccinated. This is particularly relevant for the Indian population, large swathes of which is already vaccinated against polio. It is likely that the accelerated antibody response in vaccinated individuals may inhibit a full-blown innate response by rapidly eliminating the virus. If this happens, the utility of OPV as a stop gap vaccine would be negligible.

The theory that such a stop gap vaccine might provide some immunity benefit is interesting, but need further validation. Since the onset of the outbreak, the potential positive response of various existing vaccines is being evaluated. Observational studies that countries which routinely administer polio or BCG vaccine have relatively lower mortality rate has bolstered the belief that such vaccines could boost immunity.

While taking such a vaccine may not by itself be harmful to the individual, the recommendation should account for associated moral hazards. In the absence of any clinically controlled trials there is no conclusive evidence to authenticate that these vaccines will work. Thus, making a decision to vaccinate a population in the absence of any credible scientific evidence will take away resources from the actual anti-COVID-19 effort. Further, it is likely that OPV may fail to protect from COVID-19, but people who have been administered it may feel like they have immunity and not take necessary precautions to protect themselves. These people may become exposed to the virus, creating a moral hazard associated with taking the vaccine.

COVID-19 has set scientists into a frenzy, as we race to find a vaccine or cure that could return the world to normalcy. But it is also the scientists’ responsibility to understand that their words give hope and relief to billions of people worldwide. Several times in the past 6 months have cures touted to be promising against COVID-19 been found to be ineffective. Several times people have rushed to take these untested medications, some times with severe consequences including death. It would thus be prudent to qualify such recommendations with possible outcomes of using untested medications and the necessity to continue wearing masks and sanitising hands.