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The largest study to date on the virulence of the delta variant of the coronavirus brings troubling data, particularly for the millions of people in the developing world who have yet to receive even a dose of the vaccine.
The work is centered on more than 43,000 people infected with coronaviruses in England. The average age of the studied population is 31 years. 80% became infected with the alpha variant, originally detected in the UK, and 20% with the delta, first recorded in India and now dominant in Spain and many other countries.
74% of all participants were unvaccinated and 24% received only one dose. Therefore, the work does not serve to understand the current situation in countries like Spain where the delta variant is dominant, but the vast majority of the population at high risk of covid-19 is completely immunized.
Study results, published Saturday in the medical journal The Lancet, show that those infected with delta were at twice the risk of being hospitalized for covid-19 than those with alpha.
Gavin Dabrera, a physician at the UK Public Health Agency and a co-author of the study, points out that the vast majority of participants were not vaccinated and this is essential for a good understanding of the results. The work was carried out between March 29 and May 23 this year. “We now know that vaccines provide excellent protection against the delta variant, which in the UK is already responsible for 98% of reported cases,” says Dabrera in a press release. “It is vital that all those who have not yet received the full vaccine do so as soon as possible,” he adds.
The delta variant of the coronavirus was first detected in October 2020 in India. Since then this version of the virus has spread across the world and has become the dominant one, thus defeating the alpha, or British, variant. Alpha was already 90% more contagious than previous versions of the pathogen, and a study in the UK also associated it with a 58% higher mortality. Anyway, this last data was not confirmed in other countries.
The delta variant has at least three mutations that make it potentially more dangerous. Several studies found this form of SARS-Cov-2 to be 50% more contagious than the alpha variant. A preliminary study in Scotland suggested that the delta doubled the risk of hospitalization, a fact that the work in England now confirms. The Scottish study determined which variant was present in each patient using PCR, while the current one used complete virus genome sequencing, a much more reliable method.
In the current study, one in 50 patients was hospitalized. The medical team took into account several factors that aggravate the infection, such as age, race and vaccination. After adjusting these and other indicators, they saw that delta increased the risk of hospitalization 2.26 times compared to alpha.
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There are so few vaccinated in this study, 2%, that the results do not serve to show whether the delta variant increases the severity of the disease and the number of hospitalizations among those vaccinated. Most of the studies published to date show that they are not: vaccines may be significantly less effective in preventing contagion with delta, but they are still effective in preventing severe covid-19 and death.
“Any outbreak with the delta variant among unvaccinated people will put a greater burden on hospital services,” says Anne Presanis, a UK Medical Council statistician and co-author of the paper. The vaccine drastically reduces the chances that an infected with the delta will have the disease, need hospitalization and die, he stresses.
The study authors recognize some limitations in their work. A very important one is that it was not possible to take into account the previous illnesses of the hospitalized patients, an essential factor as it can complicate the infection.
“The most important message that the study leaves us is that the delta variant means a risk only to those who are not vaccinated”, emphasizes Marcos López, president of the Spanish Society of Immunology. “Furthermore, the study is very much a slave to the moment it was done, when the delta was not yet dominant. For example, now in Spain more than 90% of cases are delta and we are not seeing a higher rate of hospitalization and severity”, he says.
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