Delta generates more supercontagions due to the long “silent” infection and the “explosive” growth of the viral load

Preliminary studies confirm that “with this variant, the growth of the viral load is explosive. Those infected can be contagious the same day they are infected”

In addition, the scientists explain that “the time you are contagious without symptoms is longer than in other variants”

Those two factors may be behind the cases of supercontagion that are taking place at outdoor events.

He pointed it out a few days ago immunologist Alfredo Corell, when talking about the risk of contagion outdoors: with the delta variant, viral loads are being seen much higher than with the previous variants. He explained that there are diagnostic centers that are finding “Positive with 5 cycles”, something that qualifies as “real outrage”.

The number of PCR cycles refers to the time it takes to positivize the sample, that is, how many are needed to detect the virus: if only a few cycles are needed, this indicates that the viral load (the amount of virus in the body) is high. The fewer PCR cycles, the higher the viral load, and vice versa. But is this of what Corell alerted is something generalized? The scientific data we have so far, although preliminary, indicates that it is. And they help understand why this variant is so contagious.

1200 times higher viral load

There are two recent studies that confirm the high viral load of the infections generated by this variant. This PHE report from June 25 compares the average viral load of the delta variant, which is 20 cycles, with that seen in the original virus, which was 30. “That means 1000 times more viral load on average in the delta variant than in the parent virus”, He assures Guillermo Aldama, cardiologist at the University Hospital of A Coruña and scientific communicator.

In this other study that was published a couple of weeks ago, Chinese scientists analyze viral loads in a delta variant covid outbreak in Guangdong. And their results indicate that “viral loads in delta infections were approximately 1000 times higher than those of earlier variant infections on the day the virus was first detected” (that is, the day the infection detected by PCR). “The relative viral loads in the delta variant infections were 1260 times higher”, they affirm.

Those infected are contagious before, but without symptoms

The scientist explains that this variant is “special” for several reasons. For starters, their incubation period is shorter: 4 days instead of 6. This might sound like good news, but it is not. Why? “Because the important thing is to see how long it takes between an infected person becomes infected and can infect another“, Explain. And with this variant, it can be “less than a day. Those infected can be contagious the same day they are infected”Warns Aldama.

This, until now, did not happen. And it is like that “because With this variant, viral load growth is explosive, much more than before. The replication of the virus in the respiratory tract is very high and very explosive ”. That is viral load reaches its maximum peak earlier.

And the most important of all: “The time you are contagious without symptoms, until they occur, is longer than in other variants.” If before you were contagious from two days before the symptoms, with the delta you can spread it for four days without being aware of it.

This has also been verified Chinese researchers in their study. They explain that their results “show that it is very likely that the delta variant is more infectious during the early stage of infection ”. And they warn of something important: “The greater contagiousness of infections with delta variant in the presymptomatic phase stands out the need for quarantine for cases of suspected infection or close contacts before clinical onset (of symptoms) or PCR screening ”.

Therefore, the researchers believe that “The frequency of population screening must be optimized. Knowing when an infected person can spread viruses is essential to design intervention strategies that break the chains of transmission “, they warn.

The fact is that delta plays with two important advantages. “The silent transmission is longer. And when you infect, you also spread more viral load “, sums up Aldama. And to these two, a third would be added, he explains. It has also been seen that “it is more efficient at entering cells, so the infection is more likely to be successful. This variant is also twice as effective ”.

Outdoor contagion is easier

Knowing all this, we can wonder if this variant generates more supercontagators. Aldama prefers to talk about “Super contagious situations, more than people.” And the fact is that you are situations are being seen more with delta than with other variants, even – and this is the worrying thing – outdoors.

The American epidemiologist Eric Feigl-Ding alert of this on his Twitter profile, he confesses “worried”, and puts several examples of supercontagion outdoors. He talks about several outbreaks at sporting events, or during outdoor concerts, which have generated thousands of infections “even among people who have not had direct contact.”

The immunologist Alfredo Corell I already explained that, “With this variant, even outdoors we cannot be calm. To get it, it doesn’t have to be a massive gathering, far from it “, warns. While at a cookout, for example, standing, without a mask and closely breathing the air that the infected person exhales, “it is clear that you can get it.” With delta you are much more likely to happen.

Higher viral load in wastewater

That the viral loads are higher with the delta variant It’s something that They also confirm us from the COVIDBENS project. Because they are seeing it daily, in real time. They are monitoring the pandemic, from the first wave, in the wastewater of A Coruña. “Not only do we sequence, we also have the ability to know what percentage there is of each variant,” he explains. Juan Vallejo, researcher at INIBIC and member of the COVIDBENS team.

“We cannot exactly determine the viral load that each patient produces, but we see the indirect effects of that, how viral load rises in sewage. We saw how the delta burst, and now we see the viral load increase, even more than we saw with the alpha”, He warns.

They know this because they measure the viral load in that wastewater continuously, since April 2020, and what they are finding now is “a much higher viral load.” But it is that, in addition, with this variant other things are happening that differentiate it from the previous ones.

“We are capable of anticipating the peaks of the waves, we act as an early warning, but this last time (in the fifth wave) we are 38 days ahead, which is a lot. Why? “Because there are many people vaccinated, there are more asymptomatic cases. We see that there is more viral load in circulation, but the health system does not detect it ”. This is clearly seen in the graphic that Juan Vallejo has shared on Twitter.

But it is not the only explanation. In the graph it is seen that, When the curve for covid cases was still falling, “we were already seeing a significant rise in the viral load in wastewater.” And he explains that this always happens, because the system takes time to detect cases, it does not do so until symptoms appear. But it is that now, as we have seen, with the delta variant, the presymptomatic phase is much longer and more contagious.

Strengthen measures, more than the vaccine

In this situation, both Vallejo and Aldama coincide with Chinese scientists and epidemiologist Feigl-Ding, and They believe that caution should be exercised and protection measures should be strengthened. “Maybe I should change social behavior, that people get scared and contract ”, says Vallejo. And that would help to stop the transmission, “without even the need for any intervention by the administrations.”

Aldama criticizes the fact that now everything is being entrusted to vaccination, and recalls that we must be aware that “what we are doing is subjecting the virus to selection pressure so that it becomes more effective. And in this, the vaccine is only one more safety sheet, you cannot remove the rest and leave the vaccine alone, because it will be a failure ”.

Because, in addition, that this variant is so contagious affects the long-awaited and mythologized herd immunity. “Group immunity depends on the contagion capacity of the virus. If an individual can infect five others, you will need to vaccinate more than 80% of the population, not 70%. But if you take measures, and get it to infect only two or three, you will need less. All this depends on the measures that are taken, more than on vaccination ”.

Aldama sums up the situation like this. “The virus should not be allowed to do tests to improve. Every infection is a test. The more tests you do, the more likely you are to be successful ”.

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