What the latest science says about a TB vaccine and Covid-19

• A new study presents more evidence that the BCG vaccine helps flatten the curve of Covid-19
• According to their model, the US would only have had 19% of actual deaths if they'd had mandatory BCG vaccine
• Further clinical trials are underway to determine whether BCG can help fight the coronavirus

Scientists are continuing to investigate whether a TB vaccine can help fight Covid-19 – and the latest study makes it look quite likely.

The Bacille Calmette-Guérin (BCG) vaccine helps fight severe tuberculosis (TB) and lung cancer, and in South Africa where we have some of the highest TB rates in the world, it's a mandated vaccine for babies. The BCG vaccine, however, doesn't prevent TB, it just considerably reduces the risk. 

This isn't the first study on BCG and Covid-19, but the study published in ScienceAdvances addresses methodological weaknesses in previous studies where the focus was more on cumulative totals of cases and deaths.

According to the researchers, "Altogether, the available evidence suggests that BCG has beneficial effects on immunity against a range of lung-related infections that go beyond TB, which makes it a promising candidate for defending against Covid-19." 

WATCH | Why are scientists testing a TB vaccine to see if it protects against Covid-19? 

30-day infection and death rates

Differing from previous studies, the researchers focused their attention on the rate of confirmed infections and deaths in each country during the first 30 days of their outbreaks.

They then compared BCG-mandated countries with countries where it isn't compulsory. Some countries terminated their BCG vaccination policies when the threat of TB was reduced, while others never had them in the first place, like Italy and the USA. 

READ | Keep TB vaccine for babies, implore experts 

Results

Analysing data from 134 countries, the researchers' graphs showed that the growth rate for Covid-19 cases was much slower in BCG-mandated countries compared to those that never instituted the policy. 

According to the researchers: "Our analysis shows that mandatory BCG vaccination is associated with a flattening of the curve in the spread of Covid-19. The effect we demonstrate is quite substantial.

"For example, our model estimates that the total number of Covid-19-related deaths in the US as of 29 March, 2020, would have been 468 – 19% of the actual figure – if the US had instituted the mandatory BCG vaccination several decades earlier."

Those who used to have the policy but terminated it before 2000 had similar trajectories to those who never had these policies. 

They also found that larger populations had faster growth rates, but that cultural markers, number of tests and reporting quality had no effect on the BCG-related trajectories. 

In terms of the death rate, BCG-mandated countries also had lower rates than those that never had the vaccine policy or terminated it. 

They also found that the rate of infection varied among BCG-mandated countries. 

LISTEN | Will BCG protect you against Covid-19? 

Limitations to BCG

The study, however, warns that the BCG vaccination might only be viable if a large portion of the population receives it to help promote "herd immunity". This means that unless a government makes it mandatory or there's a prevailing culture of compliance in a country, those who opt out due to ideological beliefs against vaccines will make it less effective. 

The BCG-Covid-19 hypothesis also has some limitations. BCG is universally administered at birth, and the science is still unclear whether it would remain effective in adults, especially the elderly. Also, while it remains effective against TB and lung cancer for decades after inoculation, more testing is needed to ascertain how long its potential effect against Covid-19 would last. 

READ | Could the TB vaccine you received at birth help protect against the coronavirus? We asked an expert

Response to earlier studies

Epidemiologist Salim Abdool Karim told Bhekisisa in April that a different preprint study on the same topic to be "fundamentally flawed" because they compared Europe and the US to Africa at a time when the epidemic hadn't had a substantial effect on the continent. In other words, the comparisons were made at a time when these countries were at different phases of the pandemic. 

While he thought it was an interesting hypothesis, when he asked his Chinese colleagues if they had seen any difference in their patients who had been vaccinated with BCG, they came back with a no.

Another expert had also previously told Health24 that another similar study – that only focused on total deaths – found that a country's testing strategy can heavily impact numbers, and that better testing in developed countries could lead to higher totals.  

He also warned against revaccination programmes for adults without more robust testing and research. 

Current trial

The BCG hypothesis is currently being tested in a clinical trial in Australia. Over 3 000 healthcare workers have signed up so far to find out whether the vaccine has an effect on Covid-19 symptoms.

The so-called BRACE trial – which has received funding from various sources, including the Bill and Melinda Gates Foundation – will build on existing research to see whether the vaccine will bring down the virus load in people infected with the Covid-19.

READ MORE | Could an age-old TB vaccine help in our fight against coronavirus?

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