A person undergoes a rapid test to detect covid in Times Square, New York, on July 27.JUSTIN LANE / EFE
The delta variant was discovered last October in India. Since then, it has expanded to a hundred countries, including Spain, where at the beginning of July it was already the majority mutation in four autonomous communities. Today it accounts for 68% of infections, according to the Report of the Ministry of Health corresponding to the week of July 12. The explosion of this variant is due to the fact that, it is suspected, it is up to 60% more contagious. This same Friday, an internal document from the US Center for Disease Control (CDC) came to light that ensures that the delta variant is more contagious than the MERS viruses, Ebola, the common cold, seasonal flu and smallpox, and is as transmissible as chickenpox. Another study, not yet reviewed by other specialists,points out that the viral load level of those infected with the delta variant, up to 1,260 times higher, may be the key factor for its high transmissibility. Although it is not the only one.
More information
The rise of the delta variant deals a new blow to the recovery of tourism
The delta variant will subtract three tenths from the strong GDP growth
The research was carried out at the Center for Disease Control and Prevention in Guangdong, China. In this city the first case of the delta variant was detected on May 21. Until June 18, 167 cases were registered. During the quarantines of the close contacts, the researchers performed PCR tests on a daily basis and took note of the amount of viral load of each infected on the first day they tested positive. Then, they compared those figures with those obtained in 63 people infected in 2020 with the original strain of covid. The group infected with the delta variant showed up to 1,260 times more viral load than those who fell ill with the first version of the coronavirus.
This higher viral load may be associated with a higher frequency of supercontagion events, as suggested by Juan Bárcena, virologist and researcher at the National Institute for Agrarian Research: “With this strain, which has higher loads at the beginning, it is easier to produce the supercontagating events ”. In these cases, a single infected person is capable of infecting 10 or more of their contacts. At the beginning of the year, an outbreak caused by a supercontagator isolated an entire block of neighbors in the town of Haro, in Bilbao. More than 30 people were infected through the building's elevators and an old ventilation system. Five of them died.
The time that passes between exposure to the virus and its detection is four days on average with the Indian variant, compared to six days on average with other strains
The close follow-up of the cases during the study also allowed us to perceive that the time that passes between exposure to the virus and its detection is four days on average, compared to six days on average that it takes with the original strain. In fact, according to the report, the government of the province began to request a negative covid test for the last 72 hours as of June 6. Just one day later, he reduced this deadline to 48 hours. During the 2020 outbreak, the current deadline was seven days. This shorter incubation period of the delta variant forces the tracking systems to operate at a higher speed, something that is not always possible due to the workload.
The study also points to the possibility that the delta variant could be more infectious in the first days of infection, before even showing symptoms.
The problem is that it is complex to measure infectivity from clinical investigations, "since less than 50% of transmission occurs during the presymptomatic phase," the document reads.
Knowing when an infected person can infect another is key to signaling close contacts, imposing quarantines or other measures, and breaking the chain of transmission.
Mutations
In addition, according to an article published in the journal
Nature
On July 28, the delta variant has different and numerous mutations, although there are three specific to this strain that make it easier for it to bind to cell receptors. In this way, the contagion would be faster and would allow the virus to partially escape from the immune system. Another study published in the same journal on July 8 found that while two doses of the Pfizer or AstraZeneca injections were capable of blocking the new strain, the level of protection it offered was somewhat lower than against other mutations. Despite this, both Pfizer and BioNTech announced in early July that they had updated their vaccine to make it more effective against the delta variant and that clinical trials would begin in August.
“There is something that is undeniable, and it is that the delta variant is imposing itself on a global scale.
That's because it has to have some advantage.
Nuria Izquierdo-Serums, head of the emerging pathogens group at IrsiCaixa
Juan Bárcena believes that despite being a study with a small sample, the figures are valid: “We are doing virological research in real time.
To be able to talk about this, it would be better to have an accumulated work of five years, with people from many countries, but we are doing things like that.
The power of the work is that they have followed the case since before they were positive.
I think it is a concrete and quick job, quite well planned and with very clear conclusions ”.
"It cannot be transferred to the population or to population studies", clarifies Inmaculada Casas, secretary of the Spanish Society of Virology. "I particularly find studies very useful, but you have to know how to value them," he insists. “These data must be viewed through the prism of the study: a highly characterized outbreak and with all its contacts detected. That at the population level is very difficult to do. That is why the numerical data that are handled with the study of an outbreak with respect to the population often do not coincide ”, he says.
Nuria Izquierdo-Serums is the head of the emerging pathogens group at IrsiCaixa and, although she is suspicious of the figures, she trusts the general results. “There is something that is undeniable, and it is that the delta variant is imposing itself on a global scale. That is because it has to have some advantage ”, he comments on the research, even without review by other scientists, a step prior to the publication of the results, which is the essential requirement to validate the work. "These data must be taken with great caution, because these quantifications have been made by comparing populations in China, but they do not say very well what the clinical characteristics of these people are. And depending on these clinical characteristics, the viral load can change ”, he warns. Izquierdo-Serums asks that the experiment be repeated with a larger sample, from different countries,to be able to confirm the results and to know definitively why the delta variant is so contagious.
You can follow MATERIA on
,
and
, or sign up here to receive
our weekly newsletter
.