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BCG vaccine and COVID-19 pandemic. Advantages and risks of BCG vaccine. (8)
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BCG vaccine is now investigated for reducing the risk of coronavirus COVID-19 infections. BCG vaccine is a century-old method of partial protection against TB, tuberculosis. But it was also shown previously that BCG vaccine had a broad ability to reduce hospitalizations and deaths in children with respiratory infections and sepsis. What are potential advantages and problems with using BCG vaccine to prevent coronavirus COVID-19 spread? call it ninety and BCG is an attenuated live vaccine and many many years ago there was a epidemiological data, which suggested that when it was introduced in Guinea-Bissau, there was suddenly a 50% drop in mortality in children under the age of five years old that couldn’t be attributed solely to protection from TB. So the vaccine protects from TB. And as you rightly said, they found that this reduction was associated with completely unrelated pathogens to TB that are involved in respiratory diseases and sepsis. So there’s been a lot of activity in the the last decade that’s trying to understand the mechanism whereby this live attenuated vaccine confers protection from unrelated pathogens. And the data suggests that what happens is the BCG vaccination induces what we call trained immunity. In other words BCG vaccine triggers the immune response in such a way that it will deal better with whatever pathogen is thrown at it. There’s been some suggestion that in those jurisdictions where BCG vaccine is standard they seem to have a lower incidence and lower severity of coronavirus COVID-19. Again, till all the data are in, likely at the end of this pandemic, it’s unclear whether this is accurate. What we do know is that there are a number of clinical studies clinical trials that are either underway or are planned that will very specifically look at the effect the BCG vaccination on protection from infection with coronavirus COVID-19 and limiting the severity of coronavirus COVID-19 disease. China is one of the countries where BCG vaccination is done routinely in children. But at the same time there is a lot of coronavirus COVID-19 infections in China. On the other hand, people get vaccinated with BCG vaccine as young children soon after birth. So the immunity might wane into the adulthood. Does that mean that people will need to be regularly revaccinated with BCG vaccine? What are the implications of the timeline of immunity against coronavirus COVID-19? Again, a very good question! And the answer is we probably don’t know yet. I mean, it’s quite intriguing because for certain cancer immunotherapies patients are given a BCG vaccination prior to immunotherapy, because they’re cognizant of the fact that that vaccination will boost an immune responses to a subsequent immunotherapy. So there was a study done a number of years ago, where healthy individuals were vaccinated with BCG and then a short time afterwards were challenged not with live virus but with the yellow fever vaccine. Now what they found was that BCG vaccination reduced the viremia in those who are infected with the yellow fever live vaccine. But BCG vaccine had no effect on the antibody response. In other words, BCG vaccine didn’t diminish the response to vaccine, but just limited the amount of virus. So I think this is good evidence that BCG vaccination will likely induce a more robust immune response to coronavirus COVID-19. BCG vaccine might enable the immune system to be better positioned to deal with coronavirus COVID-19. But the longevity of Immune response is unclear.