Paris (AFP)
The development of safe and effective vaccines is a key point in the battle against the Covid-19 pandemic which has killed more than 120,000 people, infecting only a small portion of humanity.
Why are vaccines the central issue in the fight against coronavirus? What are the current projects? What are their difficulties? When can we expect the first vaccination campaigns?
- Why are vaccines essential? -
Epidemiologists, virologists and public health experts agree that only massive vaccination campaigns would be able to effectively stop the Covid-19 epidemic.
"The development and distribution of a safe and effective vaccine will be necessary to completely interrupt transmission," said the head of the World Health Organization (WHO), Tedros Adhanom Ghebreyesus.
Containment and social distancing measures are costly, difficult to maintain over time to be effective in the medium or long term.
Treatments are currently proving ineffective in saving severe forms of Covid-19 characterized by pneumonia and fatal runaway of the immune system.
This has been the case in the past, over a much longer period, for smallpox, another viral disease without effective treatment, removed from the disease map since 1980 by vaccines.
- What projects in progress? -
The complete sequencing of the genome of the new coronavirus in mid-January 2020, then the worldwide spread of the disease, has boiled everything that the planet has in vaccine research laboratories.
The big names in pharmacy and a myriad of biotechnology laboratories are in the ranks: more than 100 vaccine projects are currently in development, according to François Balloux, researcher at University College London.
The European Medicines Agency (EMA) indicates that it is in contact with the managers of a "dozen" vaccine projects, two of which are already in the clinical trials phase.
In France, the Institut Pasteur alone carries out three "candidate vaccine" projects, while China is leading clinical trials for three other vaccine projects.
The giants of the pharmaceutical industry, the French Sanofi (France) and the British GSK hope to offer a vaccine together by next year. Their American competitor Johnson & Johnson is betting on its own vaccine formula in early 2021.
- What obstacles? -
First difficulty: the targeted virus. "So far, no one has ever made an effective vaccine against a human coronavirus," said the former director of Inserm (National Institute of Health and Medical Research), virologist Christian Bréchot.
"Cemeteries are full of vaccine candidates that have never worked," confides to The Guardian newspaper Jonathan Heeney, Canadian researcher at the head of biotech DIOSynVax, in the ranks to develop an anti-Covid vaccine.
A difficulty in developing a safe vaccine is due to a characteristic of the disease in its severe cases: the over-reaction of the immune response with its "cytokine storms", too abundant production of inflammatory substances which can kill.
How to stimulate the antiviral reaction with a vaccine without leading to a dangerous runaway of the immune machinery? "In this phenomenon, we have not yet fully understood the role played by antibodies", recognizes Frédéric Tangy, vaccine specialist at the Pasteur Institute.
"Under certain conditions, antibodies can worsen the disease," he told AFP. This was observed with some vaccines like Sanofi's dengue vaccine or a measles vaccine in the 1960s.
Additional difficulty: coronaviruses are RNA viruses which have the particularity of "mutating a lot", according to Frédéric Tangy. This makes it more difficult to develop a targeted vaccine. This is why Pasteur is also working on a "universal vaccine against coronaviruses", directed against proteins common to this family of viruses, he explains.
Another type of difficulty concerns temporality: it is easier and more effective to develop a vaccine and to distribute it before an epidemic wave.
In the midst of an epidemic, recruiting guinea pigs is more difficult because you have to be sure that they do not have or will not be infected, which would distort or complicate the interpretation of the results.
However, after the epidemic has passed, it becomes more difficult to determine the actual effectiveness of the vaccine if the virus no longer circulates in the population.
- For 2020 or 2021? -
"There is a good chance that it will work (...) Success in the autumn is possible if everything goes to perfection," confided to the British newspaper The Times, the British vaccine specialist Sarah Gilbert, professor at the University of Oxford and already engaged with its biotech Vaccitech on tests.
It makes sense to want to launch a vaccine in the fall of 2020 before a possible winter wave of Covid-19 in the northern hemisphere.
At Pasteur where the first tests will start in July, Frédéric Tangy estimates that a vaccine could arrive "at the end of autumn or at the beginning of winter".
Cautious, the EMA says: "The schedule for vaccine development is difficult to predict. Based on past experience, it could take at least a year before a vaccine is ready for approval and available in quantity sufficient to allow extended use. "
© 2020 AFP