In the coronavirus family, SARS-CoV2, its latest representative, takes center stage, to a point never reached by its predecessors. Responsible for the Covid-19 epidemic and its death procession, this virus is pushing the scientific community into a race against the clock to develop a vaccine. The general public wants to know everything about him. And to better understand it, it is undoubtedly necessary to look at the two other most aggressive members of the family, SARS-CoV1 and MERS-CoV, as Vincent suggests to us via the orange Alert us button. Could SARS-CoV2 follow the same evolution as the other two? Or could he come back every year seasonally?
Coronaviruses without great danger until the early 2000s
Coronaviruses (CoV) form a huge family of viruses which are distinguished by the exceptional length of their genomes (all of their genes). They are wrapped in a protein capsule in the shape of a crown, which gives them their name (“corona” means crown in Latin).
The first coronavirus to infect a human (HCoV) was discovered in 1965 by British researchers. Then other types of coronavirus were identified, all responsible, in humans, for more or less colds, or even mild respiratory infections. Until the early 2000s, coronaviruses were not considered dangerous enough to warrant the special interest of scientists.
SARS-CoV1, an epidemic that did not last a year
Things changed in 2002-2003 with the appearance of SARS-CoV1: SARS in English for “Severe Acute Respiratory Syndrome”, or SARS in French for “Severe Acute Respiratory Syndrome”. This virus left at the end of 2002 from the province of Guangdong, in the south-east of China, following the consumption of meat of civet (small carnivorous mammal) infected. It was later shown that the bat undoubtedly represented the natural reservoir of this virus, relates LeMonde.fr.
In six months, this virus has spread to around thirty countries on the continents of Asia, Europe and America. 8,098 people were infected, 774 died, according to the assessment of the World Health Organization (WHO). The latter sounded the alarm in March 2003. In July of the same year, the epidemic almost disappeared thanks to “isolation and quarantine measures”, tell Institut Pasteur.
MERS-CoV, an aggressive virus but a limited epidemic
In September 2012, ten years later, MERS-CoV (from the English “Middle East respiratory syndrome coronavirus”, respiratory syndrome of the Middle East) emerged in Saudi Arabia. 2,519 cases have been detected, including 866 deaths, mainly in the Arabian Peninsula, reports WHO. Studies have shown that humans contract this infection through direct or indirect contact with infected camels. If the dromedary has been identified as a vector of the virus, its origin would once again come from the bat. Human-to-human transmission remains limited. MERS-CoV has not disappeared, continuing to be transmitted at low levels.
Will Covid-19 come back in seasonal cycles?
The other coronaviruses, those which cause only simple colds, have a cycle which shows spikes of contamination in winter, explains Yves Van Laethem, specialist in infectious diseases, inter-federal spokesperson for the coronavirus crisis center. “We could fantasize about the fact that in the summer, the Covid-19 gives us a little peace, then it comes back around October, November, December. While hoping that at that time, we will have a vaccine “, judges the virologist. But you shouldn’t count on such predictions, he adds. “We hope to see him save you, but we have no evidence to say that he will come.” The most aggressive coronaviruses, such as SARS-CoV2 or MERS-CoV, did not persist with cyclicity, he points out.
The Covid-19, with a lower mortality rate, does more damage than its predecessors
“Is Covid-19 really more aggressive than SARS-CoV1 or MERS-CoV?”, asks Vincent again via our orange button. “He is less aggressive about mortality”, answers Yves Van Laethem. The mortality of SARS-CoV1 was approximately 10%, that of MERS-CoV is 35%. Regarding Covid-19, most studies show 1.5% mortality taking into account asymptomatic patients, says the virologist. If only the detected cases of Covid-19 are taken into account, the rate rises to 7 or 8%. “But this is not a good way to do it, because the cases detected mean nothing compared to the total number of underlying cases”, he specifies.
However, for the epidemiologist of the University of Rennes Pascal Crépey, the mortality rate is not really a good indication of the dangerousness of a virus: “With a more underground and quieter progression than the SARS (SARS-CoV1, editor’s note), the Covid-19 ended up touching many more people and causing many more victims (more than 350,000 dead so far, editor’s note) ) “, he explains in Release. This is for an essential reason: unlike SARS-CoV1, SARS-CoV2 (responsible for Covid-19) is transmitted before the onset of symptoms in patients. Before being spotted, they have time to contaminate others.
To develop a vaccine against SARS-CoV2, researchers are using their studies on SARS-CoV1 and MERS-CoV
“We are talking about a vaccine for Covid-19, but is there an effective vaccine against SARS-CoV1 and MERS-CoV?”asks Vincent. “There has been a vaccine for SARS-CoV1 which has never been marketed since the disease has disappeared”, Answers Yves Van Laethem. The Institut Pasteur has developed a vaccine candidate that has not been tested in humans: “When he was ready, the epidemic was happily over, and there were no more patients on whom to offer to test him”explains theInstitute.
As for the vaccine against MERS-CoV, research is underway for the animal, says Yves Van Laethem. On the one hand to cure dromedaries, so that they no longer transmit the disease to humans, on the other hand to cure monkeys. These vaccines, which have proven to be protective in monkeys, could be used to develop a vaccine for humans.
Research done to develop a vaccine against SARS-CoV1 and MERS-CoV is proving useful today in the context of Covid-19. “The know-how developed in 2003 against SARS-CoV-1, and the candidate vaccine patented in 2004, are currently applied by the scientists concerned for an ongoing project of potential vaccine against SARS-CoV-2”, says the Institut Pasteur. Thanks to its monkey study on MERS-CoV, the University of Oxford is currently “In tip”, says Yves Van Laethem, on the development of a vaccine against SARS-CoV-2.
– .
