In Depth

How the tuberculosis jab could lead to a coronavirus vaccine

Research shows correlation between levels of TB immunisation and Covid-19 cases

As the Covid-19 coronavirus spread across Europe in February and March, a surprising pattern emerged: countries with high rates of tuberculosis vaccination seemed to be succumbing more slowly.

“Eastern Europe has been less affected than the west, and even eastern Germany less than western Germany,” says The Economist.

The distribution coincides with immunisation policy, adds Euronews, which notes that “universal tuberculosis vaccination policies were widely spread in the countries of the former Soviet Union”, including the old East Germany.

Scientists have emphasised that correlation does not imply causation - with many other possible explanations for the pattern of infection - but some researchers now believe that the TB vaccination will have a role to play in fighting Covid-19.

Old vaccine, new tricks

The Bacillus Calmette–Guerin (BCG) injection, which protects against TB, is the world’s most widely used vaccine. Each year the jab is administered to around 130 million children, many of them in developing countries where TB is still endemic.

However, the vaccine has long been thought to protect children from more than just TB.

“Soon after its introduction in Europe in the 1920s, epidemiological studies reported that BCG vaccination strongly reduced infant mortality, and this could not be explained by a reduction in tuberculosis alone,” says a paper published in the journal Nature by researchers investigating whether the jab might also protect against Covid-19.

Although TB is caused by bacteria, clinical trials have shown that the BCG injection protects against viruses too, particularly those that target the throat and lungs. 

According to a report published in The Lancet, the protective effect results from “changes that enhance the innate immune response to subsequent infections, a process termed trained immunity”. That means people who have had the BCG are primed to fight off a wide range of diseases.

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Does it protect against Covid-19?

According to the World Health Organization, there is “no evidence” that the BCG works against the new coronavirus, but that may be because there hasn’t yet been time to prove the link.

In the meantime, says The Times, there is “a growing belief among some scientists [that] long-term, universal and, in some countries, mandatory vaccination” against TB offers at least some protection.

“People who have received the BCG experience a form [of Covid-19] that is easier,” Predrag Kon, Serbia’s state epidemiologist, told the newspaper.

“These are just impressions, and there is still not enough evidence to know for sure. But it does seem that the countries with universal BCG vaccinations have had an easier experience with Covid-19.”

Other potential explanations include early lockdowns, border closures and strict quarantine policies in countries with lower mortality rates.

“Political scientists in Poland and Greece say the vulnerability of health systems in Eastern Europe spurred leaders into decisive action, while governments in the west felt a ‘greater sense of complacency’,” reports the Daily Mail.

Clinical trials now under way in the Netherlands and Australia are expected to provide more insight into the possible role of the BCG vaccine.

Professor Mihai Netea, who is leading the Dutch research, said that even if the TB jab doesn’t offer comprehensive protection against the coronavirus, it “may well be a bridge to a specific Covid-19 vaccine” - which is likely to take a year or more to develop.

Why not vaccinate anyway?

Since the BCG is so widely and safely used, it may seem sensible to vaccinate first and gather the evidence afterwards. But public health officials put forward two reasons for a more cautious approach.

One is that if the vaccine turns out to be ineffective, receiving it could lead to a false sense of security. And that could encourage riskier behaviour that leads to the virus spreading more quickly.

The other issue is that lives are at risk elsewhere. “The BCG vaccine is already in short supply, and indiscriminate use could jeopardise the supply needed to protect children against tuberculosis in high-risk areas,” says The Lancet report.

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