The acceleration of vaccination campaigns against the coronavirus SARS-CoV-2 it is causing contagions, hospitalizations and deaths to collapse COVID-19 in many countries, despite the victory over the pandemic pathogen there is a threat that should not be underestimated: the new ones variants of concern (VOCs). The one that currently agitates the most experts and institutions is the infamous Delta variant, ex second Indian B.1.617.2, which is driving the new infections in the UK – became dominant around mid-May – and which according to experts’ estimates will become so in the rest ofEurope and in other countries by the summer. Why this strain of the coronavirus is so worrying compared to the others that have revealed themselves since the end of 2020? Here are its “strengths”.

Greater transmissibility

At the moment there are still no studies published in scientific journals that accurately indicate the actual transmissibility / contagiousness of the Delta variant, nevertheless the epidemiology they are making estimates based on the spread of the same. A point of reference to better understand the impact of the Delta variant is the United Kingdom, where the population is widely vaccinated and where it currently represents 95 percent of the cases sequenced, according to the latest Public Health England Bulletin (PHE), dated June 25. During a recent hearing held in the British Parliament, former Health Minister Matt Hancock, who resigned on June 26 for violating the anti-Covid regulations he himself passed, declared that the Delta variant is at least the 40 percent more transmissible of the variant Alfa, ex English B.1.1.7. According to experts, transmissibility could be up to 60 percent higher than that of the lineage that led the second wave. In the PHE document “Risk assessment for SARS-CoV-2 variant: Delta (VOC-21APR-02, B.1.617.2)”, scientists underline that transmissibility seems greater than wild type virus (first wave) “, moreover, that the Delta variant “continues to demonstrate a substantially higher growth rate than the Alfa, based on data from more analyzes”. The rates of secondary attack and studies on home broadcast indicate greater transmissibility, as well as in vitro experiments show an increase in replication in biological systems that replicate the airways of the human being
airways. In light of all this, the PHE notes, “it is very likely that the Delta variant is more transmissible than the Alfa”.

Severity of the infection

According to the study by the University of Edinburgh (Scotland) “SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness” published in the authoritative scientific journal The Lancet i Covid patients affected by the Delta variant have a risk of end up in the hospital circa double of those affected by the Alfa variant. According to epidemiologist Eric Feigl-Ding, a member of the Federation of American Scientists (FAS) and a former Harvard University professor, the hospitalization rate is 2.5 times higher compared to that of the Alfa variant and up to four times that of the original strain of Wuhan. As indicated, however, the data are still provisional and at the moment there are no definitive results, as pointed out by the PHE. “The first investigations conducted in England and Scotland suggest that there may be an increased risk of hospitalization compared to contemporary Alpha cases”, explains the British agency, however “a large number of cases are still in the follow-up period and c ‘is a limited understanding of the clinical course of the disease “.

Risk of reinfection

PHE points out that laboratory tests show the Delta variant’s ability to at least partially evade antibodies induced by a previous one natural infection. “The neutralization activity of pseudoviruses and live viruses using sera from convalescent first wave and Alpha variant infected patients show a reduction in neutralization”, however, at present, epidemiological data are insufficient to determine whether the Delta variant has a risk of reinfection actually greater than the Alfa.

Vaccine resistance

Epidemiological data and laboratory tests show a reduction in the efficacy of the anti Covid vaccines against the Delta variant, especially after a single dose. Based on data reported by the PHE, a single dose of Vaxzevria of AstraZeneca or of Comirnaty of Pfizer has an effectiveness only of 33.5 percent against thesymptomatic infection induced by the Delta variant, while with the double dose the protection rises respectively to 59,8 and al 87.9 percent. The efficacy remains high against hospitalization (and therefore against death) with the two doses of the vaccine, therefore the scientists strongly recommend everyone to undergo the vaccination and above all not to skip the recall, which is particularly valuable against the variant that emerged in India. More data is needed to evaluate efficacy based onage. It should be remembered that the effectiveness of vaccines is not 100 percent; it is no coincidence that some deaths among fully immunized people are also occurring in the United Kingdom; Among the 42 Delta variant victims found in a PHE survey, 23 were unvaccinated, 7 received only one dose of the vaccine, and 12 received both.

Delta Plus variant

From the former second Indian variant, a further lineage emerged that scientists of theINSACOG they called B.1.617.2.1 O AY.1, also called Delta Plus variant. Compared to the original Delta it is characterized by K417N mutation on proteina S O Spike already observed in the variants Beta (formerly South African) e Gamma (ex Brazilian) and that could further worsen the danger. Of the 111,157 Delta variant cases in the UK, 42 are related to this new lineage, already identified in at least six districts of three states in India (Kerala, Madhya Pradesh and Maharashtra).

General risk

According to the PHE, it is currently too early to determine whether the mortality for COVID-19 from the Delta variant is higher than that due to other lineages, however the data suggest greater transmissibility, a reduction in the efficacy of vaccines and an increase in hospitalization, which is however well contrasted by the double dose of vaccine. To better understand the impact of the Delta variant, concludes the PHE, the priority investigations are in-depth analyzes of cases and hospitalization, epidemiological studies on reinfection and characterization of generation time, viral load and period of infectivity.

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