On August 6, the US Centers for Disease Control and Prevention. they issued a recommendation on the maintenance of masks indoors. They were based on a report that the vaccinated had the same viral load in their upper respiratory tract as the unvaccinated. Since then, the dust that has arisen in this regard has been considerable. Some have taken advantage, in a display of fallacious and foolish recklessness, to ensure that, if this is the case, the usefulness of being vaccinated is called into question.
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The Discord Report
At last August 6 report, the American agency showed a study carried out with data from the state of Massachusetts, in which 469 people positive for Covid-19 in that state were analyzed and in which 74% corresponded to patients already vaccinated. The most controversial graph is the one below.
In it, it is observed that in the group of vaccinated people the same amount of virus is detected in the throat and upper airways as in those not vaccinated. That is, they have similar amounts of viral RNA.
The most immediate conclusion, and one that has been echoed by many media, is that vaccinated people spread the same as non-vaccinated people. This is not exactly like this.
Viral load and contagiousness
So far, molecular techniques for detecting virus RNA through RT-PCR technology and viral antigen and protein detection tests are the main detection methods for the SARS-COV-2 virus. Its main objective is the diagnosis of infected patients. Both have limitations and advantages according to use, frequency and condition of the patient, symptomatic or asymptomatic.
In relation to RT-PCR, several are the publications where it is shown that the Ct value, or relative viral load, at the individual level, cannot predict the transmissibility of the virus.
On the other hand, the main limitation of antigen tests is the high percentage of false negatives (which could be even higher compared to variants) during the incubation period or presymptomatic state of the infected patient. according to recent data.
A recent review analyzes whether RT-PCR techniques and antigen tests could predict the infectivity of the SARS-CoV-2 virus. His conclusion is that, for the moment, none of these techniques alone could predict the contagion capacity of the patient. Therefore, it would be necessary to establish a clinical context associated with the symptoms and the time of evolution to inform about the interruption of isolation in patients with Covid-19.
Furthermore, a sensitive and rapid method of detecting the presence of viruses would need to be developed in order to identify asymptomatic and presymptomatic people, who may have a low viral load but may still be infectious. Encouraging preliminary results have been obtained from molecular techniques using saliva samples.
Intramuscular and intranasal vaccines
Current vaccines, administered intramuscularly, act at the systemic level. They train the body and provide it with instructions so that we are able to generate defenses that protect us against possible and future exposure to the virus, once it has already infected the person and penetrated the body. They are extraordinarily effective in preventing that, even if we acquire the virus, it makes us sick; but they are not designed to keep us from getting infected.
Of another different mechanism are those vaccines that are administered intranasally, like the one being developed by the CSIC. These act by preventing infection to a large extent. To do this, they facilitate the expression of a certain specific type of antibodies, called IgA. When the vaccine is administered nasally, right at the entry point of the virus –the oral and respiratory mucosa–, those IgA are generated that neutralize the pathogen just before entering the body. This prevents infection.
This does not theoretically happen with intramuscular vaccines because they act at another level.
They would be very good for us vaccines that completely block the infection so that, once vaccinated, we would not be able to transmit it or, in other words, to be contagious to others. This, to a greater or lesser extent (much less likely that this happens if we are vaccinated than if we are not), it does happen now. In China, the CanSino company already has published the results of the phase I clinical trial of its aerosolized viral vector vaccine.
But we shouldn’t underestimate current vaccines. We have preliminary data that even intramuscular they generate that type of antibodies, IgA, in saliva and oral mucosa, although they are more typical of intranasal vaccines, more focused on defending ourselves at the same entry point of the virus.
Is it true that the vaccinated can spread the same as the unvaccinated?
Although the vaccines that are currently available initially were not designed to prevent infection, we now know that they all have this capacity to some extent after the full regimen.
In a study carried out by the Pasteur Institute recently, researchers have estimated that unvaccinated people would have a risk of the order of 12 times higher of transmitting the virus than those who have been vaccinated.
In another study, conducted in the United States with 204 first-line caregivers who were positive, mRNA vaccines were highly effective in preventing SARS-CoV-2 infection. Only 5 cases were detected in fully vaccinated people, who showed a lower viral load, magnitude of symptoms and duration of the disease compared to partially vaccinated or unvaccinated people.
In this line, a job from Imperial College from London (United Kingdom), in a majority delta variant situation, fully vaccinated people would have a 50-60% reduction in the risk of infection (even asymptomatic) compared to non-vaccinated people.
Here in Spain, a study carried out Among health and social health personnel, vaccinated people showed a reduction in the risk of becoming infected of between 80-90%.
Also, in the Netherlands, an investigation carried out To analyze the effectiveness of the vaccine to prevent transmission between vaccinated persons and close household contacts, he concluded that these showed an effectiveness against transmission of around 70%.
That is, people who have been fully vaccinated they are less contagious than those who do not get vaccinated, and also, according to data shared a few days ago, still pending peer review, the vaccinated would eliminate the virus from their body much faster way than the unvaccinated. This even in the presence of the predominant delta variant.
In other words, if you have been vaccinated, you are going to be far less contagious to others than if you haven’t. The virus is cleared from your body faster. Even if your infection is delta.
In view of the observed results, it seems clear that current vaccines, although they were not designed for this, are capable of preventing, to a certain extent, the transmission of the virus between vaccinated people. There are discrepancies in the data, probably due to the differences between the populations in which this point is studied, the circulating variants, the prevalence of vaccination and other factors.
The specific mechanisms that cause this event are unknown. One of them could be the presence of IgA in saliva and oral mucosa after administration, although we cannot be sure. Data is missing to ensure it.
In any case, that we are able to reduce transmission between vaccinated people will help us control the pandemic more quickly, without impairing compliance with other measures such as the use of indoor masks, ventilation and other non-pharmacological measures.
Let’s not forget that the measures we take have an additive nature, that is, their effects add up. Despite the extraordinary usefulness of vaccines as a tool to control the pandemic, the global percentage of vaccination has yet to rise further. Let us not forget that we are in a stage of the pandemic in which the delta variant, much more transmissible and with a dominance directed above all by its spread from asymptomatic and / or presymptomatic, forces us to be vigilant and proactive. If we want to end this pandemic, we must provide access to vaccines to countries and areas without that possibility today.
Antonio Gutiérrez is a researcher doctor and epidemiologist at the Virgen de Valme Hospital.
María del Mar Tomás Carmona is a PhD researcher in microbiologist at the Carlos III Health Institute and INIBIC.