Question asked by lewy on 03/13/2020
Hello,
The Covid-19 pandemic, caused by the Sars-Cov-2 virus, started in Wuhan (Hubei province of China) in December. The number of people affected in this country – 81,130 officially registered cases – is beginning to stabilize, suggesting a ebb of the epidemic in this region of the world.
In Europe, on the other hand, the Sars-Cov-2 is experiencing meteoric growth, with 31,500 cases accumulated on Tuesday in Italy, the most affected country on the continent, ahead of Spain (11,178 cases) and France (6,633 cases) .
Measures to limit social contact are gradually being put in place, particularly in southern Europe, with population confinement in Italy, then in Spain, and now in France since Monday, which forces people to stay at home, except to go to work or to get food.
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Containment and barrier measures
Is containment an effective barrier to stop the virus? In China, where the epidemic therefore seems to be declining, the measure, taken to its extreme, has led to quarantine some 40 million inhabitants of Hubei – before spreading with more or less severity to the whole of the country – to ban gatherings and isolate the sick.
According to a study from the University of Southampton, England, published on Medrxiv and mentioned by the site Futura Sciences, these measures would have reduced the number of infections in the country by 66%. They would even have been even more effective if they had been taken earlier, the researchers said.
“The first measures in China were taken on January 23, two days before the Chinese New Year, in Wuhan. About a month after the start of the epidemic. If they had been put in place a week before that date, the number of cases could have been reduced by 86%, according to the simulation. Even earlier action, three weeks before January 23, would have reduced the number of cases by 95% ”, reports an article by Futura Sciences.
Among the various barrier measures put in place, the researchers believe that the most effective have been the isolation of patients and contact cases, screening, limitation of social relationships, and the prohibition of gatherings. The travel bans would have had less significant effects.
On France Inter on Tuesday morning, the Minister of Health, Olivier Véran, estimated that the barrier measures in France could start to have their effects on the epidemic within a fortnight.
Problem: if these devices, particularly effective in China, because imposed by an authoritarian regime, have so far proven themselves, there is no indication that they are effective over time. Because while the barrier measures have kept the vast majority of the Chinese population away from the virus, the latter, not exposed to Sars-Cov-2, has not developed immunity. Result: if the virulence of Sars-Cov-2 seems to have diminished in this country, it could, once the measures are lifted, reappear there this summer – if the virus is not sensitive to heat – or the next winter.
Collective immunity
Other countries are taking the opposite approach, letting people be exposed to the virus, in order to generate collective immunity. Even if Prime Minister Boris Johnson denies it, this is what appears to emerge from the UK’s somewhat muddled strategy at the moment.
“Unlike the vast majority of countries, the British government has decided not to introduce drastic containment measures. No school or university closings, bans on mass gatherings (except in Scotland) “, wrote Release Friday.
“Nothing is closed, neither pubs nor schools, and concerts like this weekend in Cardiff, where 6,000 people have stuck to each other, are maintained, Our correspondent in London, Sonia Delesalle-Stolper, confirmed to us on Monday. “Even if there is a case of contamination in a school, it remains open, and the student is asked to stay at home for seven days, not even fourteen days, which is the maximum incubation time.”
“If you delete something very strongly, when you release these measures, the risk is of experiencing a rebound, at the wrong time”, explained Patrick Vallance, scientific advisor to the British government, to justify this strategy. According to him, it would be necessary that 60% of the British population is exposed to the virus to develop such collective immunity.
Under fire from critics, Boris Johnson resolved on Monday afternoon to ask the British to end social contact and non-essential travel. A “Strong recommendation”, but still no bans or closings of public places, deemed “Not necessary”.
Disadvantage of the “laissez-faire” strategy: the risk of saturation of health infrastructures – already under pressure in normal times across the Channel – leading to excess mortality in the country. According to a study by Imperial College London on the United States and the United Kingdom, and which Le Monde spoke about on Tuesday, this option, aimed only at mitigating the effects of the epidemic, “Would not prevent an increase in cases that would exceed hospital bed and resuscitation capacities by up to eight times, in the most optimistic scenario.”
Instead, the researchers suggest imposing more stringent containment measures for the virus, which are regularly streamlined and then reinstated as soon as hospitals are overwhelmed. Until the discovery of a hypothetical vaccine.
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The fact remains that the principle of collective immunity, encouraged or suffered, constitutes a route of extinction for the virus. “The higher the number of people who will have been affected by the virus, and who will therefore have developed a more or less lasting form of immunity, the less the subsequent circulation of the virus will be possible after the epidemic phase, explain to CheckNews Gilles Brücker, member of the international management of Public Assistance-Hospitals of Paris (AP-HP). The great vulnerability to epidemics is the “new” populations, those who have never seen this virus. This is the danger of new viruses where everyone is receptive. “
On France Info Sunday, the Minister of Education, Jean-Michel Blanquer, himself mentioned it: “We consider, and here I am only repeating what the scientists say, that 50 to 70% of the population end up being contaminated by the virus, and this is also what puts an end to the virus since it creates a form of majority immunity, and therefore the virus dies out by itself. ”
Heat and dryness
The third potential way for the Sars-Cov-2 to disappear, at least temporarily: the climate. “It is still a little early to be sure, but there is not yet an epidemic explosion of the virus in countries where it is currently summer. And especially in hot countries, like Southeast Asia or sub-Saharan Africa, advises Pierre-Marie Girard, international director of Pasteur institutes around the world. “It may mean that there is an important seasonal factor and that the virus can keep up with the seasons, that is something that will need to be monitored.”
According to the map of the World Health Organization (WHO), regularly updated, the Sars-Cov-2 seems indeed, as of this Tuesday, mainly present in the northern hemisphere, where winter is complete.
If the seasonality phenomenon is confirmed, this does not mean that the virus will disappear: “What disappears and appears is the epidemic”, adds Pierre-Marie Girard. But the virus is still there, and the epidemic can re-emerge once the heat and dry weather are gone. In the meantime, the epidemic is expected to have moved to the southern hemisphere, where winter will begin. With the risk also of causing a mutation of the virus, which would return even more virulent in our latitudes.
The vaccine
Last key to putting an end to the epidemic: the vaccine. But if many teams around the world have already embarked on this path, it should take between a year and two years.
Luc Peillon
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