Vaccines for Covid-19 are designed to prevent the disease that SARS-CoV-2 causes, but some researchers believe they are also effective in preventing transmission of the coronavirus.
In fact, as the number of people vaccinated against SARS-CoV-2 increases worldwide, more population data is known about the ability of vaccines to reduce infection. Clinical trials have shown that these vaccines reduce drastically symptomatic Covid-19; however, less is known about its effects on transmission between individuals.
The feeling is that as the vaccine spreads globally, we are starting to see less transmission of SARS-CoV-2 from person to person.
Now, in an article published in “The Lacent Infectiuos Diseases,” DariusMostaghimi, from the team of Akiko Iwaski, from Yale University (USA), emphasizes that “vaccines provide a moderate to excellent capacity for infection” and also explains the immunological mechanisms that make vaccines reduce transmission in a tangible and effective way .
“We observe four stages why vaccine-induced immunity can slow transmission: infection, viral replication, threshold for spread from host to host, and severity of symptoms, “they write in the article.
This researcher points out that there are studies that show that vaccines prevent transmission «at least 50% after one dose. ‘
In the article “The Lacent Infectiuos Diseases” it is described that if any of these prerequisites are not met – infection, viral replication, threshold for spread from host to host and the severity of symptoms – the virus is not capable of spread and infect.
The researchers explain that «if a vaccine can preventDuring the infection phase, that the peak protein binds to ACE2, the virus cannot infect ».
The infection phase is when the virus enters target cells. «This step – they clarify – requires that the virus lands on the respiratory mucosa of the nose and lungs of a susceptible individual, that the viral spike protein actively binds to ACE2 and that the virus infiltrates the cell. ‘
And according to the thesis of this work, “if any of these prerequisites are not met, the virus cannot infect. Therefore if a vaccine can prevent the spike protein from binding to ACE2, the virus loses its ability to infect.
In addition, they detail, vaccines prevent infection by producing greater amounts of neutralizing antibodies (NAbs). These “neutralize the infectivity of a virus.”
And remember that all vaccines have proven to be excellent at inducing the neutralization of IgA and IgG in blood.
Unfortunately, they clarify, the infection does not occur in the blood, but through the respiratory mucosa. Therefore, the brake on infection must also occur here. “To prevent infection, you have to have a lot of NAbs in these areas, nose and lungs.”
The good news is that neutralizing IgG antibody levels in the saliva of people vaccinated with the mRNA vaccines (Moderna or Pfizer).
But if the sterilization of NAbs it insufficient to prevent the virus from entering cells, SARS-CoV-2 replicates and generates a higher number of copies within its host. Fortunately, it has been seen that individuals fully vaccinated with Pfizer BioNTech, Moderna and AstraZeneca have a low viral load in nose and lungs.
For the researchers, “these immune mechanisms induced by the vaccine interrupt viral replication and prevent SARS-CoV-2 from reaching levels high enough to cause symptoms and / or transmit them completely.”
And, they continue, by keeping virus levels low, vaccines thus decrease the number of virus particles that are emitted by infected individuals.
Nasopharyngeal viral load is known to have a strong correlation with the potential for transmissibility. Thus, if there is less viral load in the mucous membranes of the nose, there will be less ability to infect.
Finally, they add, vaccines have been shown to dramatically reduce symptoms and severity of Covid-19. The result is that the pathways of spread of aerosolized microbioparticles between individuals are limited.
That is, they conclude, «vaccines can also limit the infectious period of infected individuals, in addition to transmission ”.
The fact that current vaccines may have some effect on transmission will greatly affect the course of outbreaks in countries that use these vaccines.
However they acknowledge in their work, there are doubts about the extent to which the emergent variants they can evade existing immunity and if immunity wanes over time. “The appearance of the delta variant it tests our diminishing immunity derived from vaccination and previous estimates of the efficacy of the vaccine ”, they point out.
Fortunately, he adds, booster doses are being shown to restore protection against infection.
For this reason, the comprehensive genotype surveillance viruses, clinical presentation, medical history, and demographics of people infected with SARS-CoV-2 after vaccination.
Studies in the coming months will shed light on the ultimate ability of these vaccines to prevent transmission and will identify the need or not to update vaccines.