from Silvia Turin
The level of infection in the mucous membranes of a vaccinated is the same as that of an unvaccinated subject, but does not necessarily lead to a greater spreading capacity. Fauci: Transmission from vaccinated people is a possible but rare event
I Centers for Disease Control and Prevention (CDC) USA have returned to recommending even fully vaccinated people to wearing a mask indoors in places where there are high rates of coronavirus transmission. Commenting on the decision, Anthony Fauci, White House chief medical adviser, said: It can be assumed that vaccinated people can transmit the virus as unvaccinated people can. a very unusual and rare event, but it does occur.
I vaccinated, however, they become infected much less and the chances of transmitting the virus are very low.
In promoting the vaccination campaign against Delta variant (now the dominant strain in the United States), Fauci recalled that, with full vaccination, the chances of becoming infected and transmitting the virus drop, but he also cited new scientific evidence in possession of the CDC that would show that the level of infection in the mucous membranes of a vaccinated person the same as that of an unvaccinated person. These new data would have convinced the US body to issue the recommendation on masks indoors.
What is written in the confidential CDC document
The CDC – in the document published for the first time by the Washington Post during the night – speaks of a contagiousness of the Delta equal to chickenpox. It was known. Chickenpox has an R0 (which indicates how many people a single individual can infect in the absence of measures or vaccinations) equal to approximately 5, the Delta is assumed from 5 to 8. The document states that reinfezioni of vaccinated people increase, but 35 thousand out of 162 million are in the US, equal to 0.021%. They assume that Delta will lead to more severe disease, but the more people are vaccinated, the more you will see a greater percentage of inpatient-vaccinated, but they will be concentrated among the immunosuppressed. The only real (partial) novelty concerns some studies that show huge amounts of viruses in the nose and throat, regardless of the vaccination status, the viral load. It was already known that the Delta carries viral loads up to 1,000 times higher detectable by swabs, it was not known that even the vaccinated had it. This is not the real evidence of similar transmission between vaccinated and unvaccinated, but they are certainly a reasonable assumption. There are however other researches (see the first study mentioned below, ed) who say that vaccinated people do not infect even with high viral loads.
Vaccinates infect much less
Having said this, the CDC also remember in the document that the 3-fold reduced risk of infection in vaccinees (and that of serious illness or death by 10 or more times) and that the vaccine efficacy estimates against the infection represent the average of a group, rather than an individual risk, because the risk is modified by age and health conditions, therefore if I am in an RSA, for example, the effectiveness of the vaccine and its transmission can be influenced by the context. If the vaccine, as the CDC write, is still 80% protective of the infection, it means that among the completely vaccinated the Rt less than 1 also for the Delta.
How contagious is a vaccinee?
In the absence of other specific studies on Delta transmissibility, we must rely on similarities with the other variants. How contagious is a Delta infected vaccine? The variable depends on two factors: vaccine efficacy and transmission capacity. We know that a well-protected vaccine: this protection, which concerns the single person, is measured on entry with the data on the effectiveness of the vaccines (usually calculated only on the symptomatic ones). The transmission capacity (or the rate of secondary infections), on the other hand, determines the potential for a contagious vaccine to infect others, hence the lack of protection at the exit. However, there are no published studies on this factor so far.
What is the effectiveness of vaccines?
The efficacy of vaccines used in Italy is estimated to be 88.15% for those immunized with 2 doses. The latest British data speak of a protection (with 2 doses) against the Delta from 65 to 90 percent. Let’s think of a closed environment with one or more positives: if those present are all vaccinated, 35 out of 100 are infected in the worst case; if they are not vaccinated, the percentage can rise to 100%. Vaccines prevent infection because uninfected individuals cannot transmit it.
What is the viral load?
High but not total protection: can the 35 infected people still transmit the virus? As there are no published studies on this variable, we must rely on those carried out when the Alpha variant dominated. They have shown that the chances that a vaccine can infect are very low. The most recent study on the subject released Wednesday in the New England Journal of Medicine (Nejm) from Israel: it monitored reinfections on 1,497 healthcare workers. 74% of the positives had a high viral load, however this did not lead to any secondary infection, i.e. none of them infected other people. The study, which ended on April 28, mainly concerned cases of Alpha. Another research on domestic transmission in England found that family contacts of cases vaccinated with a single dose had about 40-50% reduced risk of becoming infected. Published in the Nejm on June 23 and coordinated by scientists from the British public service (Phe), it was related to the Alpha variant, as it ran until February 28. Similar studies have also been conducted in the US and Israel: again on the Nejm the CDC published a research carried out up to 10 April on 3,975 health professionals. A 40% lower mean viral load was found in positive vaccinated subjects. The other Israeli survey was carried out in February and published in Nature on March 29: it analyzed people who tested positive after the Pfizer vaccine. Viral load was reduced 4-fold for infections occurring 12-28 days after the first dose.
The vaccine shield
The research carried out on the Alpha variant leads us to believe that, even considering the greater contagiousness of the Delta, the vaccinated are protected from contagion (between 65 and 90%) and, even if infected, they are unlikely to transmit the virus. Until new evidence, therefore, if there is me in a room, vaccinated that I contracted the virus, in any case it will be less infectious than those who tested positive without being vaccinated. More: if I am in a closed room, my infectious capacity will be practically nil against a vaccinee, who in turn is protected from contagion (more or less, depending on the doses he has done). Basically there are two shields that protect us. If I meet an unvaccinated person, I will be little contagious, but she will have no protective shields and will be totally susceptible to my (albeit weak) virus.
What remains to be understood
The unknown factor remains the peculiarity of the Delta and to understand how (and if) it behaves differently from the other variants. We know that its run does not stop thanks to its ability to infect, estimated between 40 and 60% higher than the Alpha variant, in turn 50% more infectious than the original Wuhan strain of Sars-CoV-2. From a recent research by Chinese scientists published online and not yet reviewed, we also know that the viral loads measured on Delta variant infections were 1,260 times higher than the values of previous strains. Fauci himself, however, pointed out that there are no clinical data on what high viral loads mean in terms of transmission: they do not necessarily involve a greater capacity for spreading the virus. What is certain, because it has already been calculated, is that to a large extent the vaccines also block the contagions of the formidable Delta: the English national health system (Phe) has estimated that up to 23 July, vaccines have prevented 22 million infections. And it should not be forgotten that these drugs were not designed to stop the infections, but to save lives: in England the deaths avoided so far would be 60 thousand (source Phe) and in Italy in the last six months the vaccination campaign would have avoided almost 80. % of casualties we would have expected based on previous wave numbers.
July 30, 2021 (change July 30, 2021 | 15:18)