CHRONQIUE : We have discussed the concept of herd immunity during a previous column, the best ways, by using an example particularly convincing, the remarkable control (but not even noticed elsewhere) for our 1.064 marine 1.767, aboard the aircraft carrier Charles-de-Gaule, who in just 5 weeks, have won the battle against them as fast and as unexpected infection by the SARS-COV-2.
All healed !
Sweden, has caused much ink to flow when it decided not to confine, with a focus on herd immunity, against the detention class, vulgarisant and to the whole World this therapeutic strategy.
We all know that the influenza-like illness, the immunity acquired by the population in contact with the virus, more than the vaccination, we can stop the epidemic.
The Institut Pasteur offers the following definition : “herd immunity is the percentage of a given population that is immune/protected against an infection from which an infected individual introduced into the population is no longer going to transmit the pathogen because it encounters too many subjects protected. This immunity of a group or collective, can be obtained by natural infection or by vaccination (if a vaccine exists, of course) “.
He adds that the level of herd immunity necessary to stop the epidemic, however, could be lower if :
1. the number of contacts with others is very different according to the persons within a population ;
2. children under the age of 10-12 years were less susceptible to infection with the new coronavirus ;
3. there is a cross protection with the coronavirus seasonal.
We already knew since the 6th April and the online publication in the Lancet a systematic review fast, that the second condition was satisfied.
We are going to learn today that the third was most likely also !
Herd immunity is often called “immunity of the herd ” (Herd immunity) in the anglo-saxon
Even the Professor Karine LACOMBE, Head of the infectious diseases service at the hospital Saint-Antoine AP-HP, Paris, spoke on June 25, during his hearing by the inquiry committee of the national assembly :
“Will there be a second wave, there are a lot of parameters to take into account. In particular, the immunity. If this is an acquired immunity in contact with the virus, as it exists at present, cross-immunity, and we are starting to have a lot of data that shows that there may be cross-immunity conferred by exposure to other coronavirus, the coronavirus responsible for the common colds “
The information below is derived from scientific articles recently published on the subject, or more exactly, pre-published (which means that they have not yet been subjected to critical review by peers), as there was an emergency broadcast while the pandemic is not totally complete. Mainly 4 items that you will find the references at the end of this column. Two were written by a researcher, French, Hélène BANOUN, Pharmacist, biologist and former research officer at the INSERM. An article from a team of researchers from the famous University of Oxford and the fourth is the result of a research conducted by british authors (Oxford, Edinburgh, Glasgow), brazilian (Sao Paulo) and the Portuguese (Porto)
It is striking in examining the curves of the epidemic of coronavirus in the late stage current, a change in the world towards goodness. The appearance of new cases is prolonged, but at the same time, we are seeing a steady decline in the severe forms and deaths.
The low proportion in the population of individuals who have developed a symptomatic form of the covid-19, can be explained by the existence of cross-immunity between the SARS-COV-2 and other coronaviruses responsible for viral infections benign. This phenomenon is based on cellular immunity. In contrast, humoral immunity, mediated by antibodies, and tested using the ” serology “, could be in part responsible for some of the phenomena immuno-pathological.
The role of humoral immunity in the cross immunity has not been demonstrated. It is then necessary to turn to the cellular immunity to understand this phenomenon is favorable.
The balance between this cellular immunity is beneficial (not tested routinely), and these events, immuno-pathological, could explain the low number of sick children and the high lethality (mortality among infected individuals), in the elderly.
To better combat a future pandemic respiratory virus emerging, it would be necessary to improve the protection of frail and vulnerable, and at the same time, boost the immune defenses of the world’s population to a point of view of overall health.
Recent history, particularly the acquired knowledge with the SARS-COV-1 during the 2003-2004 outbreak, seem to have been a little neglected. In effect, the role of cross-immunity between other coronaviruses (pathogens of common colds), or SARS-COV-1, has been advanced to explain the low proportion of individuals who have developed the covid-19 and also the small number of people living with hiv with the tests currently available.
We know that for the coronavirus, but the SARS and MERS, antibodies (humoral immunity) disappear after 2 or 3 years, whereas the cellular immunity persists 11 years.
Coronaviruses have all in common an envelope with spicules, in English, ” Spike proteins “. These proteins look like a crown to the virus, hence the name coronavirus. See the figure below
A study (to 2020) has been demonstrated in patients who had developed a covid-19 moderate, 83% of them had CD4+ cells capable of recognizing the antigenic determinants, called ” epitopes “. Another team, also in April 2020, showed that among young adults cured of an infection is mild or moderate SARS-COV-2, 100% of their CD4+ and 70% of their CD8+ (lymphocytes ” killers “), were reactive. In relation to persons who are not exposed to the virus, the responsiveness of their CD8+ t cells to the structural proteins (membrane and nucleocapsid of the virus) and non-structural sars coronavirus in human non-hazardous waste (HCov) is known.
So we have the studies to the results of convergence which tend to prove that there is cross-immunity between colds mundane and covid-19.
This immunity is directed logically against antigens common to all coronaviruses, and not against the specific antigens of SARS-Cov-2. These antigens are common are found on the structural proteins N (nucleocapsid), M (membrane) and Spike and also on the non-structural proteins (including the enzymes for replication of the viral RNA). This cross-reactive immunity may thus explain the low percentage of patients Covid-19 among the population (except in the elderly, and the chronically ill).
The coronavirus believed to be responsible for 15% to 20% of colds in adults.
Note : Coryza or common cold, acute Rhinitis, of infectious origin or not. The coryza is one of the conditions that are most prevalent. The entire population is affected each year under variable frequencies (on average of 6 to 10 episodes in children 2 to 4 adults). It is most often caused by a virus (rhinovirus) and is highly infectious to close (Source).
According to different works, the severe forms of covid-19, with respiratory distress and support in the icu, are associated with cytokine production in significant quantities. For the severe forms in the icu we talked about ” storm of cytokines “. Cytokines represent a heterogeneous group of proteins or glycoproteins soluble, among which, TNF-alpha, interleukins, the interferons… They are involved in the immune response to infectious agents and pathogens.
The Pr Eric Vivier, Immunologist, Public Assistance – Hospitals of Marseille, interviewed on cross-immunity by Jean-Jacques Bourdin, 29 may 2020 :
While it was commonly accepted that the threshold of herd immunity (SIC) required to prevent a resurgence of SARS-CoV-2 was greater than 50 % regardless of the epidemiological context, two papers, pre-published this month on the platform Medrxiv, show that this threshold can be reduced significantly if a fraction of the population is incapable of transmitting the virus due to an innate immunity or cross-protection from exposure to the coronavirus.
Good new non.
If this is true, why, then, have locked up the $ 51 million of French and French as well for eight weeks, and have hidden behind masks since Monday, 20 July ?
Covid19 : cross immunity with other coronaviruses, phenomena immunopathological. Hélène BANOUN. July 2020 (here)
Evolution of the SARS-CoV-2 face the immune system of its host. Hélène BANOUN. July 2020 (here)
The impact of host resistance on cumulative mortality and the threshold of herd immunity for SARS-CoV-2 Medrxiv. July 2020 (here)
Herd immunity thresholds for SARS-CoV-2 estimated from unfolding epidemics. Medrxiv July 2020 (here)
Author(s): François Pesty for FranceSoir