Coronavirus
Another Reason the US Is Struggling More With Coronavirus than Some Nations Abroad: BCG Vaccination
The latest research indicates countries where a vaccine for tuberculosis is mandatory have reduced spread of Covid-19. What does that mean for the United States?
The idea that the BCG (Bacillus Calmette–Guérin) vaccine, first administered in 1921 to prevent tuberculosis (TB), may have some protective effect against Covid-19 has been gaining traction in recent weeks. Take a look here for more background on how TB, BCG, influenza, and Covid-19 are related:
Research published on August 5th by Martha Berg, et al. in the Journal of Science Advances adds further legitimacy to this concept. In their article titled, “Mandated Bacillus Calmette-Guérin (BCG) vaccination predicts flattened curves for the spread of COVID-19,” Berg and colleagues eloquently describe a clear correlation between administration of the BCG vaccine and reduced spread of the novel coronavirus. Let’s unpack their findings.
The investigators looked at data from 134 countries showing the rise in cases and deaths from Covid-19 at the pandemic’s outset while comparing nations that mandate BCG with those that don’t. The authors explain further,
“Over the last century, many countries adopted universal policies of mandatory BCG vaccination to fight against tuberculosis, which was then a major threat. Since then, many countries maintained such a policy, at least until very recently (e.g., China, Ireland, Finland, and France). Some other countries terminated the policies as tuberculosis ceased to be a threat (e.g., Australia, Spain, and Ecuador). Of note, some countries never mandated BCG vaccination (e.g., United States, Italy, and Lebanon).”
Below is a graph on a logarithmic scale showing that nations who mandate BCG vaccination (blue line for the average and blue dots for the individual country) experienced a much slower rise in cases and deaths once the novel coronavirus entered their borders.
To display their data in another way, Berg and colleagues plotted the virus growth rate adjusting for a number of factors unique to each country including age, population density, and migration patterns. The evidence is again convincing that the BCG vaccine offers some level of protection against Covid-19.
Anticipated questions
Why did investigators only look at data from the beginning of the pandemic?
It is true that this study only compared data from the first month of the pandemic whenever it occurred in each country. This was done to eliminate variations among nations in regard to reporting bias, which includes testing infrastructure and availability. As long as such biases remain the same for an individual country over the course of the pandemic’s first month, their effect can be considered minimal.
Although not precisely correlated, the rate of initial Covid-19 spread can be thought of as a surrogate marker for how the virus goes on to propagate after the first month since many of the countries with slow initial rates are also seeing a fewer percentage of cases and deaths multiple months into the pandemic.
How does the TB vaccine protect against the novel coronavirus?
The answer to this question is not entirely clear, but it is thought to occur through the innate branch of the immune system, as opposed to the adaptive branch, through a process called trained immunity. For more details on these two branches of the immune system, please take a look at this story:
The basic idea is that the BCG vaccine, which is considered a potent immunomodulator, may be training the innate immune system to work more efficiently to activate the adaptive immune system, which is ultimately needed to overcome Covid-19. This non-specific pathway is different than the mechanism BCG follows to create immunity against TB. Previous studies have suggested the BCG vaccine can protect against yellow fever and influenza in this non-specific manner as well.
Why isn’t it routine to receive the BCG vaccine in the US?
TB has a low prevalence in the US and, as it turns out, BCG is not all that effective against TB reducing cases only by about 20–30%.
Should we all go out and get the BCG vaccine?
The short answer is, no. Even though there appears to be a protective effective effect on a population level, there is no data from prospective trials that would suggest an individual could achieve a significant level of protection against Covid-19 from the BCG vaccine. Additionally, since the BCG vaccine is typically administered at birth, it is unknown how quickly the vaccine could train the immune system to fight Covid-19, if at all. Even Berg and her fellow investigators state, “BCG is by no means a magic bullet that assures safety against COVID-19.”
Fortunately, there are prospective trials underway to investigate the effects of BCG on individuals who may become exposed to the novel coronavirus. My suspicion is that while it’s possible the principles used to make the BCG vaccine a strong immunomodulator may play a role in the development of a vaccine for Covid-19, the BCG vaccine itself will not prove to be a valuable intervention in the US.
