Secrets of the Delta variant: contagion even with two doses and when they expect community circulation

Paula galinsky

08/22/2021 2:46 PM

• Clarín.com

• Society

Updated 08/22/2021 4:51 PM

Delta is still on everyone's lips and, according to specialists and Government Health referents, there would be little left to confirm the

community circulation

in the country of this variant of the coronavirus.

For a long time, it has been repeated that it is necessary to

complete vaccination schedules

to mitigate its impact, which already caused the first death in the country this Sunday.

However, it is not yet so clear how it behaves among those who received the two doses.

These people, who today represent 25% of the population, could they become infected and spread?

The answer is yes.

From this it is that two experts explain what are the chances of contracting Delta among the "immunized", if they are expected to experience serious symptoms and what we should do to stop its advance.

“It is known that Delta

partially escapes the action of vaccines

and that, for that reason, both doses are needed.

Completing the schemes is very useful to prevent serious disease but

not contagion

”,

Jorge Geffner, doctor in Biochemistry, senior researcher at Conicet and professor of Immunology at the UBA School of Medicine

tells

Clarín

.

Mouth, nose and throat

The trigger to address this issue is a report from the US Centers for Disease Control and Prevention (CDC). "The agency had said that in some areas the vaccinated

could avoid the chinstrap and now they had to backtrack,

" says Geffner. It was after confirming that during the first days of the Delta infection the virus remains and can be amplified in the upper airways of the vaccinated person. That is, in the

mouth, nose or throat

.

“For approximately

5 days

, the infected vaccinated can transmit the virus at similar levels as an unvaccinated person.

But later, due to the effect of the antibodies, the virus

does not progress to the lower airways or the lungs

and so, in most cases, complications such as bilateral pneumonia are avoided ”, he says.

He clarifies that the reported situation is with two doses of Pfizer although he considers that the panorama is similar with complete schedules of other vaccines, "either Sputnik V, AstraZeneca, Sinopharm or combined."

Microscopic image of Covid-19 captured by scientists in the United States.

Delta's viral load is much higher than that of the other variants.

/ AP

As an example of the importance of two doses against severe disease, Geffner provides collected data on what happens one day at

Houston Medical Center

and

Perry Hospital

in the United States. “On August 9 there were 81 hospitalized between the two health centers: 72 not vaccinated and 9 vaccinated. 23

of them

came to intensive care,

none of them with a vaccine

, and of those 23, 11 were ventilated, ”he says.

Along the same lines, the specialist shares the reasons why he insists so much on completing the diagrams. “Vaccines generate antibodies, which serve to block a small part of the

S protein

- RBD - that the virus uses to bind to and infect cells in the body. The available vaccines are made with the old RBD, that of

the original Wuhan virus

. The mutations that resulted in the Delta variant modified the RBD. This makes it more difficult for the antibodies to recognize it and that both doses are needed. The same thing happens with the

South African variant

”, he explains.

And it adds details on the effectiveness in terms of protecting against infection comparing Delta with Alpha (UK variant) and what happens with one or two doses of Pfizer and AstraZeneca (separately), according to a study published in July of this year in the

New England Journal of Medicine

.

The percentage of effectiveness is located near 33% among those who received a dose and face Delta, against 50% against Alpha.

The percentages are

between 60% and 88% with two doses

, the level of protection being higher with Pfizer.

"And, extrapolating the data, the levels against severe infection would exceed

90%

with two doses," Geffner remarks.

Based on this information, he concludes that vaccination with two doses is essential.

“Fortunately, there is good adherence in the country and it does not happen like in the United States, where between 30% and 35% of adults chose not to get vaccinated.

We must continue to complete schedules with either homologous or heterologous vaccination.

Progress is being made but more slowly than we need ”, he assures.

The use of the chinstrap is essential to prevent contagion of the Delta variant.

Photo Luciano Thieberger.

According to the Conicet researcher, now that we know that even with two doses the person is contagious, it is very important that

social distance

is still respected

, that meetings are held

outdoors

or in ventilated places and that

the chinstrap is used

.

“The drop in the number of cases and serious cases leads to new openings, something that is good.

But there are decisions like the one that boys do not wear a chinstrap in schools that I don't think is appropriate ”, he says.

Meanwhile, he maintains that within a month we will surely have Delta community circulation.

"It is not clear to me the magnitude, it is not yet known if we will experience something similar to what happens in Europe or it could happen as in Brazil, where the Manaus variant continues to predominate," he says.

And he adds: "The path with Delta installed must also be accompanied by

more tests

and by good epidemiological surveillance based on

genomic sequencing

."

Specialists say that a single dose of the Covid vaccine is not enough against Delta.

Photo Mariana Villa / Los Andes

Jorge Quarleri, biochemist, professor of Microbiology at the Faculty of Medicine of the UBA and principal investigator at Conicet, agrees with Geffner that the virus infects the upper airways of people with a complete vaccination scheme.

“At that point,

the viral load levels are similar 

between vaccinated and unvaccinated.

The difference arises later, when the infection wants to thrive towards the lower tracts.

It is there where it finds the resistance of the response generated by the vaccine and, consequently, it is expected that those with two doses will not become seriously ill ”, he details.

"On the contrary, the unvaccinated have a higher risk of experiencing serious symptoms, with a higher rate of hospitalization and a

poor prognosis,

" he highlights.

It also agrees that for an average of 5 days the virus can survive and reproduce in the nose, mouth or throat and the person has a chance of infecting it.

“In some cases it can spread more and in others the viral load will decrease sooner.

Age is one of the influencing factors

, also the time that has passed since the infected person was vaccinated ”, he remarks.

And it refers to the results of an unpublished manuscript of a study conducted between May and June from a Delta outbreak in China's Guangdong province.

"From this work it appears that people infected with Delta are more likely to

spread the virus before developing symptoms

than those infected with other variants," he says.

"A thousand times greater"

He says that airborne transmission is much higher than with other mutations (between 40% and 60% more contagious) and that, for all this, the chinstrap is essential.

"

The viral load is a

thousand times higher with Delta

when compared to others," he warns, based on a preprint carried out by authors from China and England.

“This is not the time to relax in contagion prevention.

Those who did now are back with many cases.

I mean the United States, Great Britain and Israel ”, he highlights.

And he affirms that having 25% of Argentines with two doses is still not enough: “We must increase the figures drastically before Delta circulates in a community way. It should also be taken into account that two weeks after the application of the second dose are necessary to achieve a solid immune response.

With a single dose, the protection is close to 30%

”.

Asked about those who are vaccinated and had Covid, Quarleri maintains that the risk of infecting it is lower.

“The person who has already had the disease surely has higher levels of protection in the upper air tract because the virus entered there.

Such

robust mucosal immunity

is rarely achieved with traditional vaccines.

To that end, aerosolized vaccines administered by the nasal route are being developed ”, he closes.

MG - EMJ

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