On March 11, 2020, the WHO officially declared the coronavirus epidemic as a “pandemic”. A time that now seems very distant, and during which research on the SARS-CoV-2 virus, discovered a few months earlier in China, was still in its tentative stages. Transmission, lifespan, mutations… One year later, where are our knowledge of the virus and its disease, Covid-19?
What we know
- Several modes of transmission
The mode of transmission of Covid-19 most often mentioned is transmission by droplets, these invisible secretions projected during coughing, but also during discussions, in a perimeter of less than two meters. It is now considered that close and prolonged contact with an infected person is necessary in order to be infected in turn by these respiratory droplets.
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The issue of transmission by aerosols, tiny particles remaining suspended in the air, has also often come up in the debate. In July WHO recognized “The possibility of aerial transmission in public places”, “Especially in very specific conditions, such as overcrowded, closed, poorly ventilated places”.
Here too, prolonged contact would be necessary to allow infection in an enclosed and densely populated area, which is why room ventilation has been added to the list of preventive measures.
“Aerosol contamination occurs mostly indoors and not outdoors, says Jean-Claude Manuguerra, head of the emergency biological intervention cell at the Institut Pasteur, interviewed by “l’Obs”. Outside, we have a rapid dissolution of aerosols. “
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Another mode of transmission studied: contact with contaminated surfaces. A study by the Australian National Scientific Agency revealed that SARS-CoV-2 can survive for up to 28 days on smooth surfaces, such as banknotes or smartphone screens, but only under certain conditions. Here too, however, this mode of transmission is much less frequent than that by droplets.
- Masks are effective in preventing transmission
Useless at the start of the epidemic in France, it has gradually become mandatory in public places. The mask has since been considered as one of the essential tools in the fight against the transmission of Covid-19. The surgical model, filtering at 95%, is the most recommended today for daily use. Home-made masks are much less so, because they are considered less effective against Covid variants.
- English, South African, Brazilian variants… Several mutations observed
Like all viruses, the new coronavirus has mutated. The appearance of variants worries the whole world since the end of 2020. Because if the mutations are sometimes without consequences, the new variants appear to be more contagious, to the point that they became the majority in France in February.
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What remains uncertain
- The impact of the virus on children and their contagiousness
Contagious, not contagious, more affected, less affected … For a year, studies on the impact of the coronavirus on children have been saying everything and its opposite. “Children are infected but many develop symptomatic forms”, observe Jean-Claude Manuguerra. If they are sensitive, they do not transmit the virus in its current form, he emphasizes, recalling in passing a study by the Institut Pasteur affirming that schools are not places of amplification of the epidemic. .
- Duration of immunity
How long are you protected after catching the virus? The question is the subject of particularly careful analysis by the scientific community. According to a study published in January, the protection would last at least 8 months.
“The many studies published on post-infectious immunity show that things are quite complex, tempera Jean-Claude Manuguerra. It is difficult for the moment to draw general trends. “ According to him, it will be necessary to wait for new studies, and especially time, to reach certainties.
Time is also what it will take to learn more about “long Covid” and the long-term effects of the disease. Today, we still do not really know why some patients with Covid-19 present for months with symptoms such as extreme fatigue, breathing difficulties or neurological and cardiac disorders, a long-term condition that affects one in ten patients according to WHO. The organization called on health authorities around the world to treat the topic as “of the utmost importance.”
- The influence of temperature and humidity on the epidemic
Is the virus sensitive to heat or cold? The impact of temperature has often been discussed, especially last summer, when the epidemic calmed down. A study published in late 2020 by Predict Service stated that temperatures between 3 and 17 ° C were most conducive to the circulation of the virus, and hypothesized that droplets evaporate or fall to the ground depending on temperature.
This hypothesis should however be put into perspective: “The link between temperature and hydrometry and viral resistance exists, but it is not absolute”, warns Jean-Claude Manuguerra. If the temperature is a disadvantageous factor, it is especially in an outdoor environment, he explains, recalling in passing the changes in behavior linked to temperature, which can also affect the epidemic.
- How will the epidemic evolve
Will the virus be overcome one day? Jean-Claude Maguerra is pessimistic: “I don’t think we’ll ever get rid of it, he believes. It will be necessary to ensure that the impact of the virus is as little as possible on the population. This will involve monitoring and surveillance of Covid-19, but also through medical countermeasures, such as vaccination. “
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A vaccination that will have to be adapted according to our knowledge, because, he recalls, certain mutations, such as those present in the Brazilian and South African variants, have modified the antigenicity of the virus (that is to say , its ability to bind to certain parts of the immune system), which may be a problem, although partial, with vaccines.
“Will we have to be vaccinated every year?” Every ten years? “, asks Jean-Claude Maguerra. The future will tell.
