Developed over many years of bacterial culture, without modern laboratory methods or basic knowledge of genetics and genetics: the BCG tuberculosis vaccine – short for Bacillus Calmette-Guérin, old-fashioned after its French discoverers – has been an old-school drug for more than a hundred years old. Could this active ingredient play a decisive role in the fight against Sars-CoV-2?
What seems unlikely is actually being tested by scientists from several countries. At the Dutch Radboud University Nijmegen Medical Center and in Melbourne at the Murdoch Children’s Research Institute, doctors vaccinate elderly people as well as doctors and nurses who are particularly exposed to the virus. In Germany, the newly developed tuberculosis vaccine VPM1002 – a variant of the BCG vaccine with fewer side effects – developed by immunologist Stefan Kaufmann at the Max Planck Institute for Infection Biology – will also be tested on healthcare workers and the elderly
The agent trains the non-specific part of the immune defense
At first glance, there is little to be said for the comeback of the old vaccine: to date, around 100 million children worldwide are vaccinated with it every year, but this is mainly due to the fact that doctors simply do not have anything better to fight against tuberculosis. How effective the vaccine is is controversial. The Robert Koch Institute assumes 50 to 80 percent protection. Where there are few cases of tuberculosis, as in Germany, the vaccine has long ceased to be a routine vaccine.
However, the idea that BCG could have an effect beyond protection against tuberculosis is not new. As early as 1931, Swedish researchers reported in the Revue de la Tuberculosethat the introduction of the vaccine greatly reduced the number of children who died – more than it could be explained by the protection against the lung disease alone.
A vaccine usually only protects against the virus or bacterium, of which it contains individual building blocks or a weakened form. The vaccine does not make you sick, but it triggers the production of specific immune cells in the body. In an emergency, these can then multiply quickly and produce antibodies against the special pathogen.
However, scientists such as the Danish anthropologists Peter Aaby and Christine Benn suspected that BCG would have an additional effect: The tuberculosis vaccine also trains the innate, non-specific part of the immune system – such as cells that release crucial messenger substances to combat pathogens or absorb pathogens.
In this way, BCG may also protect against viruses. There is clear evidence of this, as the research group of the Dutch immunologist Mihai Netea was able to show in a review in 2019: Flu-sick mice, for example, have fewer viruses in the blood if they were previously injected with the tuberculosis vaccine, and thus less lung damage in the end. “These effects of tuberculosis vaccination on innate immunity have brought Covid-19 to the fore again,” says immunologist Stefan Kaufmann. Scientists hope that these mechanisms also strengthen the immune defense against the novel coronavirus. Covid-19 could possibly prevent serious, life-threatening illnesses, particularly in the body of older people whose immune systems are weakened.
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A recent study by New York researchers points out that this could work. They examined BCG vaccination rates and corona case numbers in different parts of the world. Countries without routine BCG vaccination – such as Italy, the United States and the Netherlands – have higher mortality and disease rates than countries where children are usually vaccinated. The researchers concluded: A high number of BCG vaccinations may reduce the number of Covid 19 diseases and deaths.
The findings could be too late for the current pandemic
Christoph Lange, Medical Director at the Research Center Borstel, Leibniz Lung Center, objects: “In the current situation of the ongoing pandemic, it cannot be assessed whether these differences in the number of cases are really due to the BCG vaccination.” Too many other factors play a role: people in different countries are of different ages, have different pre-existing conditions, and the handling of the coronavirus is different. That is why there is a need for the studies that are starting now, in which vaccinated and non-vaccinated participants are as similar as possible – and scientists can compare them well.
But regardless of the outcome of the studies, one thing is already clear: vaccines developed precisely against an exciter provide more comprehensive protection – this also applies to Sars-CoV-2. “VPM1002 and BCG would only be interim solutions until a specific vaccine is available,” says Stefan Kaufmann. There is also a risk that the findings for the current pandemic come too late. Christoph Lange fears: “Even if the studies are carried out as quickly as possible, many people will have been ill by then.” However, the researcher adds: “In the event of future outbreaks of pathogens against which a suitable vaccine is not immediately available, experience will be available”.
Note: In an earlier version, it was said that clinical studies on the vaccines are already underway in Germany. However, these are only in preparation and have not yet started.
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