After disinfection on nanoparticles, mortality and adverse effects at trial stages or links with stroke, opponents of vaccines against COVID-19 continue to spread new misleading arguments.
The latest concerns a rare but already observed immune mechanism with some vaccines: the facilitation of infection by antibodies. Antivaccine since they discovered its existence Claims that vaccines against COVID-19 not only protect their hosts, majority of he is ill, which, according to him, would explain the unprecedented wave of contamination in Europe. But these claims are not based on any scientific observation.
What are convenient antibodies?
Adjuvant antibodies are antibodies that, instead of neutralizing the virus, will facilitate its replication and, therefore, infection of new cells. They are generally indistinguishable from neutralizing antibodies made by the human immune system. Once produced by B lymphocytes, antibodies will recognize nearby coronaviruses and physically bind to them by attaching themselves to their surface proteins (spicules, or spike proteins). Nothing out of the ordinary, so far. These antibodies then recruit immune cells that will phagocyte the virus to destroy it.
By binding to the virus, the antibody has the function of “recruiting” immune cells, which will destroy the virus.
Classically, antibodies associated with a virus “attach” to a macrophage via its receptor (called FcγR), the macrophage “swallows” and “digests” everything (these are the endocytosis and lysis steps). However, in the case of infection facilitated by antibodies, at the time of endocytosis, the neutralizing chemical bond between the antibody and the virion may prove fragile and “rupture”; The virion then “escapes” and can then infect macrophages, in which it replicates as a Trojan horse.
Infection may also be facilitated by an immune hyperreaction caused by antibodies. By binding to the virus, these act to “recruit” immune cells, which will destroy the virus. But this recruitment sometimes causes a chain reaction of immune cells and excessive inflammation that will turn against the body. Respiratory pathogens often drive this activation pathway.
Infection by antibodies is mainly facilitated during the second viral infection, in subjects already infected but who have encountered a strain different from the first virus. Exposure to a virus that is nearly identical, but has different surface proteins, weakens the neutralizing ability of antibodies.
Cases of convenient posterior infection have been documented for some human coronaviruses, including SARS-CoV-1, the virus responsible for the SARS epidemic in 2003. But most of the known cases involve the dengue virus.
Example of Dengvaxia in the Philippines
These mild infections can be dangerous and may upset the risk-benefit balance of the vaccine to such an extent that its marketing authorization is revoked. This is what happened with the vaccine against dengue fever (Dengvaxia) developed by Sanofi-Pasteur. It was suspended in the Philippines in December 2017, when the laboratory warned the government that children who had never been infected with the disease were to be protected by it if they contracted the virus after vaccination. Instead they are at special risk. There are five different serotypes of the dengue virus, and it is common for a second natural infection with a different serotype to lead to a more severe infection due to insufficiently neutralizing antibodies. This is the mechanism seen with Dengvaxia.
Establishing a case balance sheet is not easy. Nineteen deaths from dengue have been recorded in vaccinated minors, without a clinically established link to the vaccine. Philippine officials pursuing legal action against Sanofi say they are investigating more than 600 deaths that may have been directly linked to the vaccine. However, the data, methods and technical explanations given by the authorities did not reassure the Filipino medical community or dengue fever experts.
Occasionally, infections have been facilitated by vaccines targeting other viruses:
- Some older measles vaccines that use an inactivated version of the virus sometimes lead to more severe infections after vaccination. They are no longer used and have been replaced by those using attenuated but live versions of the virus.
- A vaccine developed in the 1960s against respiratory syncytial virus, the most common cause of lung infection in infants, had similar problems with inactivated viruses. Its development stalled and never came to fruition.
The rare feature of infection by antibodies reported in the history of vaccinology is often caused by inactivated or attenuated virus vaccines, as in the case of Dengvaxia.
What about Covid-19 and its vaccines?
Some cases of COVID-19 have already been suspected of smooth transmission. Recent work by a Chinese team published in the journal virus In December 2021, sera of healthy patients showed in vitro traces of facilitated infection. A case of a 25-year-old American being infected with two types of SARS-CoV-2 twice in two months, a second time with a more severe infection, was described in October 2020. the Lancet, A higher viral load or a more virulent virus may explain the clinical severity of the second infection, but the authors do not rule out that it may be an antibody-mediated infection.
In early 2020, the risk of facilitative infection in the vaccinated population was a topic of discussion in the scientific community during the development phase of current vaccines. The researchers wanted to minimize the risks by targeting the spike protein of SARS-CoV as specifically as possible. -2, so that the neutralizing activity of the antibodies produced remains sufficient to avoid facilitating infection. Data from clinical trials of two messenger RNA vaccines by Pfizer-BioNtech and Moderna, published in the fall of 2020, do not indicate any cases of infection facilitated by vaccination.
Cases described in the medical literature are very rare, and such a mechanism has not been observed in SARS-CoV-2 infections or among vaccinated populations. A single publication, dated September 2021, differs from the relative existing consensus, but reports only indirect observations that prove nothing and do not reassure the community of immunologists. It has not been taken up by any other study and is only cited by Antivaccine on social networks.
If contamination by vaccines against COVID-19 or SARS-CoV-2 facilitated and exacerbated subsequent infections, the pharmacological surveillance and scientific community would have already observed and documented it at even lower frequency. However, it is not so. In contrast, all data accumulated in real life on current vaccines shows a high degree of protection against severe forms of the disease.
In France, data from the Department of Research, Studies, Evaluation and Statistics, which cross-reference hospital data with vaccination status, shows that vaccinated individuals are grossly underrepresented in severe forms: In the same population, they are nine times less present than non-vaccinated and fourteen times less admitted to critical care than the latter. Vaccination with boosters is even less, This vast difference between vaccinated and non-vaccinated forms of severe or fatal forms of COVID-19 was observed in the United States from November 2021, but also in Switzerland, Chile or England.
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