Oral Polio Vaccine (OPV), Pregnancy, and COVID-19

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How do we get the body to fight off a potentially deadly virus? There are three basic strategies. One is that you can use medicines that interfere with the virus’s ability to infect human cells and or that interfere with its ability to reproduce into new little baby viruses once it gets inside the cells. Currently, researchers are running clinical trials on various medicines that can do either of these two things. Another strategy is to give something to people that teaches the immune system to recognize the virus as something foreign that must be neutralized. This is called vaccination, or immunization. It makes use of a phenomenon called adaptive immunity, meaning that the immune system is able to adapt to build defenses specific to a particular threat. The third strategy consists of treatments to improve the way that the immune system responds to agents to which it has not adapted, a phenomenon known as innate immunity.

Whereas vaccines are usually developed with hopes that getting the immune system to adapt to a particular infectious agent or toxin will keep people from ever suffering any symptoms, and while this often works, with antiviral medicines, usually the idea is that the medicine will simply reduce the severity of the illness and shorten the duration. This weakens the infecting agent while also giving your immune system more time to rev up and the combination defeats the illness. The same concept applies to the strategy of boosting innate immunity. Treatments are expected mostly to minimize the severity of the illness, improving the body’s odds of overcoming the illness altogether.

The most obvious element of innate immunity is your skin. As a physical barrier, the skin keeps a lot of potentially disease-causing agents from entering your body. The acid in your stomach also helps with innate immunity as it can destroy a whole range of microorganisms, rather than adapting to fight off any particular one. But innate immunity also involves a range of chemicals and immune cells, providing several opportunities for treatments that can modulate the immune response. Possible treatment opportunities that researchers are studying that involve boosting innate immunity include the BCG vaccine (covered recently here on The Pulse). This is a vaccine that was developed against the bacterial species that causes tuberculosis, meaning that it was created for the purpose of stimulating adaptive immunity against tuberculosis. However, scientists are finding that certain vaccines, including BCG, appear to boost innate immunity as well. This is a very big issue when it comes to COVID-19, because not all countries give BCG to children. The reason is that it is not fully effective in preventing tuberculosis, yet those who get vaccinated experience positive reaction to skin testing for the disease. As a result, tuberculosis screening efforts can be confused, leading many countries to decide that the partial protection provided by vaccine is not worth the screening confusion. There are three groups of countries: those that give BCG, those that used to give BCG but stopped giving it, and those that never gave BCG. The latter group, the non-BCG countries, includes the United States and Italy, where the spread of COVID-19 and the numbers of deaths have been particularly horrible, whereas the former group, the countries that give BCG, includes various countries in sub-Saharan Africa, where COVID-19 rates have been notably low. Certainly, there could be genetic factors at play –people in sub-Saharan Africa have been notably more vulnerable to HIV, the virus that causes AIDS, compared with other genetic groups. However, the observations regarding BCG and COVID-19 are enough that scientists have raised eyebrows.

On top of this, research over the years has suggested that the BCG vaccine may reduce the vulnerability of people to other viral diseases. And the same may also be true for another vaccine, namely the oral polio vaccine (OPV), also known as the Sabin vaccine, after the researcher who developed it in the 1950s, Albert Sabin.

In the United States, the Sabin vaccine is no longer given, but it was administered to children from 1963 to 2000. If you were a child during that period, you may have received it. It would have been something that your doctor or nurse gave you to drink, a kind of vaccine that would not have made you cry, as it is not a shot. Overlapping with the use of OPV and continuing to this day has been a different polio vaccine, namely the Salk vaccine, named for a different scientist, Jonas Salk, who lived in the same time period as Sabin. Unlike OPV, the Salk vaccine is injected, but it’s the Sabin vaccine, the one that you drink, that some scientists believe may possibly boost innate immunity in a way that can be helpful against COVID-19.

An important word of scientific caution. At present, there are not enough data for scientists to conclude that OPV would be an effective treatment or preventive measure against COVID-19. It is speculative, a hypothesis. However, unlike BCG, which is attached to some concerns and uncertainties regarding its safety in pregnancy, no particular pregnancy dangers have been documented for OPV. While this does not mean that you should run out to get a dose of OPV, it does mean that, in the event that the science turns out to show that OPV is useful against COVID-19, or against viral outbreaks of the future, then most likely the treatment will be available to pregnant women.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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