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Covid An internal US report assures that the Delta variant is as contagious as chickenpox
Health Is a third dose of the Pfizer vaccine against Covid really necessary?
The
Centers for Disease
Control and Disease Prevention
(CDC) in the
US have once again recommend that even people fully vaccinated
using a
mask
in
indoor
places where there are high rates of transmission of the
coronavirus
. In announcing the decision, Anthony Fauci, the White House's chief medical adviser, said: "It can be assumed that vaccinated people can transmit the virus as unvaccinated people do. It is a very unusual and rare event, but it does happen." .
The vaccinated, however, are infected much less and the chances of transmitting the virus are very low.
In promoting the vaccination campaign against the
Delta variant
(which is now the dominant strain in the United States),
Fauci
recalled that with full vaccination the chances of becoming infected and transmitting the virus decrease, but he also cited "new scientific evidence" in the possession of the CDC that would show "that the level of infection in the mucous membranes of a vaccinated person is the same as that of an unvaccinated person. "
These new data would have convinced the US body to issue the recommendation on the use of
the mask indoors again
.
The CDC speaks of studies that "will be published shortly" and some scientists have called for them to be available immediately, but so far no one has read them.
How contagious is a vaccinated person?
How contagious is a vaccinated person infected with the
Delta variant
?
The variable depends on two factors: the efficacy of the vaccine and the transmission capacity.
It is known that a vaccinated person is well protected: this protection, which concerns the person, is measured by data on the efficacy of vaccines (generally calculated only on symptoms).
The transmission capacity (or the rate of "secondary infections"), on the other hand, determines the possibility of a contagious vaccinated person infecting others, hence the lack of "outgoing" protection.
However, so far there are no published studies on this factor.
How effective are vaccines?
It is estimated that the efficacy of the vaccines used in Italy is 88.15% for those immunized with 2 doses.
The latest British data speak of a protection (with 2 doses) against the
Delta variant
of 65% to 90%.
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 go up to 100%.
Vaccines prevent infection because uninfected people cannot transmit it.
What is "viral load"?
Protection is high but not complete: can the 35 infected people continue to transmit the virus?
As there are no published studies on this variable, we must trust the studies carried out when the Alpha variant dominated.
These studies have shown that the chances of a vaccinated person becoming infected are very low. The most recent study on the subject was published Wednesday in
Israel's
New England Journal of Medicine
(Nejm). Monitored reinfections in 1,497 health workers. 74% of the positives had a high viral load, however this did not lead to any "secondary infection", that is, none of them infected other people. The study, which ended on April 28, concerned mainly Alpha cases.
Other research on domestic transmission in the UK found that household contacts of cases vaccinated with a single dose had a reduced risk of infection of between 40% and 50%.
Published in the Nejm on June 23 and coordinated by scientists from the British Public Service (Phe), it was related to the Alpha variant.
Similar studies have also been conducted in the US and Israel: again on Nejm, the CDC published research conducted through April 10 on 3,975 healthcare professionals.
A 40% lower mean viral load was found in positive vaccinated subjects.
The other Israeli poll was carried out in February and published in
Nature
on March 29.
He tested people who tested positive after the
Pfizer
vaccine
.
The vaccine shield
The research carried out on the
Alpha variant
leads us to think that, even considering that Delta is more contagious, those vaccinated are protected from contagion (between 65% and 90%) and, even if they are infected, they have little chance of transmitting the virus.
Until new evidence, therefore, if I am in a room, vaccinated, but infected, in any case I will be less contagious than those who tested positive without being vaccinated.
Moreover, if I am in a room indoors, my contagious capacity will be practically zero compared to a vaccinated person, who in turn is protected from contagion (more or less, depending on the doses he has taken).
In practice there are two "shields" that protect us.
If I meet an unvaccinated person,
I will be "not very contagious"
,
What remains to be understood
The unknown remains
the peculiarity of Delta
and understanding how it behaves differently from the rest of the variants.
It is known that its career does not stop thanks to its ability to infect, estimated between 40% and 60% more than the Alpha variant, in turn 50% more infectious than the original Wuhan strain of
Sars-CoV-2
.
Thanks to recent research by Chinese scientists not yet reviewed, it is also known that the viral loads measured in the
Delta variant
infections
were 1,260 times higher than the values of the 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 imply a greater ability to spread the virus.
What is certain, because it has already been calculated, is that to a large extent vaccines also block the contagion of the "formidable" Delta.
The British national health system (Phe) has estimated that as of July 23, vaccines have prevented 22 million infections.
And don't forget that these drugs were not designed to stop infections, but to save lives.
In the United Kingdom the deaths averted so far would be 60,000 and in Italy in the last six months the vaccination campaign would have prevented almost 80% of the casualties that we would have expected according to the numbers of the previous waves.
According to the criteria of The Trust Project
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