April 23th 2020, by Christelle Tamby, PhD
The Covid-19 pandemic is now affecting the entire world. In France, if no action had been taken, this coronavirus could have caused hundreds of thousands of deaths. The current lock down measures, that should last for a minimum duration of nine weeks (by successive extensions), has been decreed by the authorities. It aims at limiting the disease spread to control the increase in serious cases that would overload already congested hospitals. Hospitals could not cope with more cases and mortality would rise consequently.
An epidemic ends when the population reaches its threshold of herd immunity, i.e. a sufficient percentage of the population has developed immunity to the pathogen. The virus could therefore not infect these individuals, who will then no longer be vectors of the disease.
As a potential short-term solution, one scenario regularly comes up among the replies: the emergence of a COVID-19 drug treatment allowing an accelerated exit from lock down. Currently, more than 50 clinical trials are underway with a large majority of molecules in therapeutic repositioning. This strategy offers the possibility of accessing a treatment quickly on the market.
Repositioned molecules in trials can be:
Antivirals used in the treatment of other viruses,
Molecules used for other pathologies, including non-infectious ones,
Molecules whose action on the SARS-CoV-2 virus has been documented in vitro,
Molecules selected for their known mechanism of action.
While the world is waiting for the development of a vaccine, two major approaches are currently being investigated: on the one hand, a treatment directly targeting the viral cycle for early therapies and, on the other hand, an approach aimed at modulating the immune response, whose overactivation is responsible for serious cases of delayed onset. The development of serotherapies, consisting in directly injecting the plasma of cured and immunized patients, is of interest because they would make it possible to support the immune system of patients against the virus. These treatments could make it possible to limit the mortality rate of the disease and relieve the congestion in the intensive care units. However, they would not prevent the spread of the disease.
The hypothesis put forward by the majority of the Labtoo community is an exit from lock down beyond 30 days. Currently, the vast majority of European countries have decreed the lock down.
The purpose of lock down is to break the chain of disease transmission and to limit the appearance of new cases over time, and therefore statistically limit the number of serious cases, so as not to saturate hospital intensive care units and to be able to take care of all patients who need it.
However, lock down has a very high economic cost: the Banque de France reports a 6% loss of GDP in the first quarter, with an additional loss of 1.5% for each additional fortnight of confinement. It is therefore necessary to determine an optimal duration that would hurt the economy as little as possible while slowing the spread of the virus as much as possible.
In a strict containment model without leaving home, the ideal duration would correspond to the maximum incubation time (about 14 days for Covid-19) added to the average time a patient remains contagious. At the end of the lock down, there would thus in theory be no more vector and the exit could be done in a safe way.
In practice the containment can never be total because apart from certain professions that continue to work on a daily basis, we are also allowed to go out to make essential purchases. The transmission of the virus, although its rate is dramatically reduced during this period of lockdown, will still take place, which will generate residual cases that will remain beyond. There are two possibilities for the authorities to decree this exit.
An earlier exit than that recommended by the scientific expert council would allow a rapid resumption of economic activity in the country. However, the number of residual cases will most likely cause further spread and a second epidemic peak.
Such an increase in the number of cases would result in the need for a new lock down period of several weeks. We would then lose the benefits of the first containment period and there would be a severe impact on the country's economy.
A longer lock down period would mean continuing to observe a significant slowdown in the French economy in the immediate term for better long-term benefits. Extending the period will allow time for the hospital's intensive care units to decongest and reduce the number of residual cases that will circulate on discharge, thus greatly limiting the risk of a second epidemic peak. However, these residual cases will be the source of new outbreaks of the disease, which could lead the authorities to cyclically resume restrictive measures, less drastic than a lockdown, as explained by Prof. Alain Fischer. This scenario would favor a gradual recovery of the country's economic activity without further major disruptions.
In any case, the end of the lockdown must be followed by surveillance measures to control the spread of the virus.
One way to limit the risk would be a massive population screening before release, with positive patients being placed in quarantine. The development of serological screening will provide two types of information: the infection status of people tested, and the proportion of people immunized against the virus, or immunological coverage of the population. This data will make it possible to better assess the possibility of new epidemic episodes emerging and to adapt measures to limit their impact until the threshold of herd immunity is reached. One possibility raised by Anthony Fauci, director of NIAID, USA, is that the virus may become seasonal, like influenza, which will require cyclical management with annual vaccine development.
The way out of lock down will not mean a return to normal life as many people hope. Beyond a national upheaval, the closure of borders at European level could be maintained for as long as each country locally contains the epidemic in order to avoid new massive contaminations. France is experiencing its first major health crisis of the 21st century and hospitals will take several months to return to normal functioning.
While interesting results are featured in this non-reviewed study, it also presents some limits:
In the longer term, lessons will be learned from this pandemic, particularly at the national level, where questions about the reconstruction of public hospitals and funding of research, which plays a crucial role in the outcome of this epidemic, will have to be addressed seriously.
Indeed, for several years now, researchers have regularly denounced the difficulty of funding to carry out their research according to the subjects studied, as well as a much too few permanent positions in the sector.
Today, some scientists have received emergency funding in order to quickly find a solution to this pandemic, but these funds arrive too late to avoid serious consequences, both in terms of health and economic consequences, as Bruno Canard deplores in an interview in Le Monde. It is necessary to reconsider research as a long-term investment with essential groundwork to be able to better anticipate this kind of crisis in the future.
On an individual level we can also maintain in daily life the reflexes learned or reinforced during this crisis, namely barrier measures to limit the spread of coronavirus, and other infectious diseases.