A group of scientists have a striking proposal for keeping people safe from covid-19. In a new paper published Thursday, they argue that we can use existing vaccines like the oral polio vaccine to provide some degree of temporary immunity against the coronavirus.
The authors include scientists at the U.S. National Institutes of Health as well as Robert Gallo, one of the researchers who discovered HIV. As they explain in the journal Science, the theoretical concept of repurposing vaccines for other diseases is actually pretty old, dating back to when the oral polio vaccine was first widely used in the 1960s and 70s.
They cite studies of mass vaccination campaigns suggesting that the vaccine—which can induce immunity to three types of the polio virus—reduced mortality or sped up recovery from other viral diseases, like the flu and genital herpes. Polio vaccination in children has also been linked to lower rates of ear and respiratory infections as well as diarrhea, all of which can be caused by bacteria and viruses.
Immunity to a certain germ can come from antibodies and other immune cells that form soon after a new infection and are created specifically to disable it. But it’s our innate immune system that’s the first line of defense. Scientists theorize that some vaccines are capable of rallying the innate immune system to provide greater non-specific immunity against most any foreign invader, at least for a short while. That might be especially helpful for covid-19, the authors write, since it’s suspected that the disease may suppress the innate immune response.
“This is something that’s been discussed in the past, even at the World Health Organization level,” Melvin Sanicas, a vaccine and infectious disease researcher who has worked with the WHO but is not affiliated with the new paper, told Gizmodo via email. In 2013, he noted, the WHO formed a working group that concluded that several vaccines (the polio vaccine wasn’t studied) could theoretically provide a non-specific protective effect against infections; the WHO went on to agree that the findings merited further research.
Sanicas added: “With regards to polio, the oral polio vaccine has been shown to provide protection against infections other than polio, so there is enough scientific justification to evaluate it for induction of a ‘boost of antiviral mechanisms’ against SARS-CoV-2.”
This protective effect only seems to come from vaccines that use a live (but weakened) version of their target, like the oral polio vaccine. Similar effects on unrelated infections have been seen for live vaccines for measles and tuberculosis, the authors noted. But the polio vaccine might be a more appealing option to rejigger into a temporary shield against covid-19, given its ease of use, low cost, and existing infrastructure to mass-produce it (despite polio being nearly extinct, over a billion doses are still produced annually as part of an eradication program in several countries).
Of course, no vaccine or drug comes without potential side effects. The oral polio vaccine, for instance, can rarely cause outbreaks of the weakened polio virus in areas with poor water sanitation and low pre-existing immunity (the weakened virus can sometimes survive in a vaccinated person’s feces, mutate, and then infect someone who isn’t vaccinated). But these cases are typically milder than the classic form of polio, and outbreaks can be stopped through vaccination campaigns. The risks of vaccine-derived polio are still easily outweighed by the benefits of vaccination.
The most pressing question, though, is whether existing live vaccines can actually protect against covid-19 well enough that they would be useful during the pandemic.
“The hypothesis that non-specific vaccination could boost resistance to any viral infection by inducing innate antiviral responses is plausible, although it’s unclear how long that would last,” Angela Rasmussen, a virologist at Columbia University, told Gizmodo via email. “If the oral polio vaccine is inducing a transient innate response that then goes away relatively quickly, it’s not clear to me that heightened innate immune responses would provide sufficient protection to be of substantial benefit to public health.”
Given the plausibility of the theory, though, the authors are advocating for clinical trials using the existing stock of oral polio vaccine. At least one trial is being planned in the U.S., according to a statement released by the Global Polio Eradication Initiative in April. There are also at least two clinical trials underway studying whether the Bacille Calmette-Guérin vaccine, used for tuberculosis, can improve immunity to covid-19 infection.
If such trials end up finding a significant benefit, then this strategy may not only become a preventative measure for covid-19 but for the inevitable next pandemic.
“If proven to be effective against covid-19, emergency immunization with live attenuated vaccines could be used for protection against other unrelated emerging pathogens,” the authors wrote.