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The Delta wave in England

Despite the deployment of anti-COVID-19 vaccines in the 1st part of 2021, the number of cases and deaths linked to SARS-CoV-2 continued to increase in the northern hemisphere prior to the summer. The increase in cases was due in part to the emergence of the Delta (Indian) variant, which quickly became dominant at the expense of the Alpha (UK) variant. British researchers (at Imperial College, London) followed the exponential growth of the Delta variant in England and analysed the efficacy of vaccines.

They used data from PCR tests in England from the 20th of May to the 7th of June (period 1), and from the 24th of June to the 12th of July (period 2). For each period, data from about 100 000 patients was used. In addition to information concerning positive results, the scientists gathered other information on the patients, such as their vaccination history. They observed that between the 2 periods studied, the number of SARS-CoV-2 infections increased significantly. During these 2 periods, the Delta variant became dominant and supplanted the Alpha variant. Young people, the sector of the population that was least vaccinated, were the most affected by infections during these periods. The scientists showed that individuals who had received 2 doses of the vaccine had a reduced risk of infection (1,2% risk of infection for unvaccinated people, against 0,04% for those who were vaccinated).

After this period, the arrival of summer meant numbers of cases lessened, probably due to the school holidays and people spending more time outdoors. But will the colder weather and the persistence of the Delta variant bring about a 5th wave this winter?

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