A study carried out jointly by the British government and the University of Oxford determined that adults who have fully vaccinated against the coronavirus can reach infection levels as high as those who were not inoculated, if they are infected with the strain. delta. On the other hand, it was reported that it is unlikely to achieve herd immunity.

The Guardian newspaper publishes that while there is evidence that Pfizer and AstraZeneca’s Covid vaccines provide broad protection against death and severe cases, this new analysis shows that although being fully vaccinated reduces the risk of infection, it does the person eventually contracting the Delta variant of the coronavirus may have virus levels similar to those of unvaccinated people.

Sarah Walker, professor of medical statistics and epidemiology at the University of Oxford, explained that “we still do not know how much transmission can occur among people who contract Covid-19 after being vaccinated; for example, they can have high levels of virus, but for shorter periods of time “, while adding:” The fact that they can have high levels of virus suggests that people may not be as protected from the delta variant as we expected ”.

On the other hand, the study ensures that the complete schedule of the Pfizer / BioNTech vaccine is initially more effective against the Delta variant than that of the AstraZeneca / Oxford preparation, but the efficacy of the first one declines more quickly. The research, led by experts from the University of Oxford, detected that, in infections with high viral load, the protection of the Pfizer vaccine one month after the second injection is 90% greater than that present in unvaccinated individuals, but it falls 85% and 78% after two and three months, respectively. In the case of AstraZeneca, the equivalent protection offered by this preparation was 67%, 65%, and 61%, respectively.

The study, which has not yet been reviewed by the scientific community, analyzed data from the British National Health Service (NHS) collected between December 2020 and August 2021. In addition, experts examined the tests of 700,000 patients taken before and after the last May 17, when the delta variant became the dominant one in the UK.

Their results, the authors explain in a statement, suggest that those who contract covid-19 from the delta variant after the second puncture have peak levels of virus similar to those of unvaccinated people. Likewise, they emphasize that although the preparations do not eliminate the possibility of contracting the disease, they do reduce the risk of contagion and are still the most effective way to guarantee protection against the delta variant.

“We still do not know how much transmission people who contract COVID-19 can cause after being vaccinated. They may have, for example, high levels of the virus for shorter periods of time,” explains Walker. However, he points out, the fact that these patients may have high levels suggests that “people who are not vaccinated may not be as protected against the delta as we expected.” “This means that it is essential that as many people as possible are vaccinated, both here in the UK and around the world,” Walker adds.

His colleague Koen Pouwels notes that although Pfizer and AstraZeneca show “slight decreases in protection” against “all infections” and “infections with high viral load”, the overall efficacy of the vaccines is “still very high.” In parallel, the experts also found that a dose of Moderna preparation (developed in the United States) has an efficacy against the delta variant “equal or greater” than the other two vaccines, but they still do not have data to evaluate its effectiveness after vaccination. full guideline.

Regarding the intervals between doses, the study found that this factor does not alter the effectiveness of vaccines to prevent new infections, while detecting that the younger groups (18-34 years) have higher levels of protection than those of older (35-64 years). The researchers noted that their findings could serve to advise the Joint Committee on Vaccination and Immunization (JCVI), which must decide whether to recommend a third booster dose in the fall.

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