Paris (AFP)

Could the good old BCG preserve the caregivers of the Covid-19? While the development of a vaccine specifically targeted against the coronavirus will still take months, several studies are verifying the possible protective effects of the tuberculosis vaccine.

"We have known for decades that BCG has non-specific beneficial effects", that is to say that it protects against diseases other than the one for which it was created, tuberculosis, explains to AFP Camille Locht, Inserm research director at the Institut Pasteur in Lille.

Children vaccinated with BCG suffer less from other respiratory illnesses, it is used to treat certain bladder cancers and it could protect against asthma and autoimmune diseases such as type 1 diabetes.

The hypothesis is that the tuberculosis vaccine could have a similar effect against the coronavirus, either by reducing the risk of being infected, or by limiting the severity of the symptoms.

Health professionals are "the first target who should benefit from this approach", judges Camille Locht, who is finalizing the protocol of a clinical trial for France, because they are among "people most at risk of developing the disease" and they must be protected first.

However, the researchers remain cautious before claiming that BCG has a shield effect against the coronavirus.

- "Military exercise" -

"This is precisely the reason for this research," insists Mihai Netea, professor of experimental medicine at the Radboud University Medical Center (Nijmegen), who announced two weeks ago the launch of a clinical trial with the University of Utrecht, involving 1,000 healthcare professionals (500 will receive the vaccine and 500, a placebo).

"If there are fewer people in the group vaccinated with BCG who must stop work because of the disease, it will be an encouraging result," added this recognized specialist in "trained immunity".

This recent concept illustrates the discovery that our acquired immune system (the one that develops antibodies) is not the only one with memory. Our innate immune system can also be prepared to better combat attacks, thanks in particular to live attenuated vaccines, such as BCG or measles.

However in the case of Covid-19, in addition to infection by the virus, there occurs in severe forms an excessive immune response, with the uncontrolled production of pro-inflammatory proteins, cytokines.

"Vaccination, in particular against BCG, could help to better orchestrate this inflammatory immune response", explains Laurent Lagrost, Inserm research director who works on these links between inflammation and the immune system.

The vaccine acts as a "military exercise in peacetime" to "fight the enemy effectively in wartime," he said Tuesday, interviewed by BFMTV.

In Australia, a team of researchers from the Murdoch Institute in Melbourne also launched a large trial including 4,000 caregivers in hospitals across the country.

"We hope to see a reduction in the frequency and severity of Covid-19 symptoms in healthcare workers who have been vaccinated with BCG," said team leader Nigel Curtis.

In France, where BCG was compulsory until 2007, "most of the study participants will have already had a first vaccination", but the protective effect of this decreases over time, observes Camille Locht.

This microbiologist wants to harmonize the criteria of the study with that planned in four Spanish hospitals, in order to better compare their results.

In Spain, researchers would like to use not BCG, but a new vaccine developed by the Galician biotech Biofabri.

This vaccine candidate, whose safety has already been demonstrated, should offer "better protection", said AFP Carlos Martin, professor of microbiology at the University of Zaragoza, because it is "developed from of a strain isolated in humans "while" BCG is prepared from a strain of the bacteria that infects cattle ", and because two genes very important for the virulence of tuberculosis have been deactivated there, this which makes it more protective.

Another advantage: made in Europe, it would be quickly available, while BCG suffers from severe supply tensions and using it for adults with Covid-19 could deprive children of it in countries where tuberculosis is still present. endemic.

In Germany, the Max-Planck Institute for Infectious Biology (Berlin) is also preparing a trial with a genetically modified vaccine candidate, developed by the laboratory Serum Institute of India.

"In parallel" with these countries, there is "a reflection on a deployment in Africa" ​​of comparable clinical trials, announced Thursday Inserm.

This should be done as part of the call for tenders launched Wednesday by the National Agency for Research on HIV and Viral Hepatitis (ANRS) "to urgently support research on COVID-19 in resource countries limited, "says Camille Locht.

© 2020 AFP