Does the Delta variant of Covid weaken the effectiveness of vaccines? –

The Delta variant, B.1.617.2 (previously called Indian), in our country: the latest report from the Istituto Superiore di Sanit dating back to May 18 speaks of a prevalence of 1% and the recent case of an outbreak in a gym in Milan in which there was at least one sequenced case, that of a already vaccinated (with two doses) infected by the Delta.

In the UK, 68 per cent of cases are in unvaccinated people

The case of reinfection which raises a series of questions about the Delta: how often can it cause infections even in people already vaccinated? The variant capable of lowering the protection given by vaccines? The first answers to these questions come from UK, where the Delta variant has now supplanted the Alfa variant (formerly English) and constitutes 96% of cases, but above all where the sequencing of the new positives are so numerous that they have reached 88% of the total, thanks also to a new genotyping test that uses a highly specific mutation as an indicator of the Delta variant. The British data just released by the National Health Ministry (PHE) on 11 June are, therefore, particularly accurate and speak of 33,207 total cases of Delta variant in the week, a significant increase compared to the 9,426 of the previous week. It is estimated that the transmission capacity of the Delta is greater than 64% and increases the risk of hospitalization by 2 times, but what kind of population is it spreading to? 68% of cases occurred in unvaccinated people: the analysis of a cohort with very frequent tests, that of health personnel, shows very low numbers of reinfections (4 in the last week). A strong concentration of positives too in young people between 10 and 29 years. Very few (less than 5%) cases involve people aged 60 or over. This aligns with 2-dose vaccination coverage for the UK. Even in the country that first started the vaccination campaign, in fact, there are about 2 million over-50s who are not vaccinated, 13 million unvaccinated young adults and an additional 8 million partially vaccinated young adults.

Hospitalizations and deaths

The other fundamental issue is whether the vaccines in use are still able to offer protection in the event of contagion with this variant. In the UK, while the rate of case increase is as strong as last fall, hospital metrics are climbing more slowly. THE there are shelters, but they are increasing rapidly among young adults (ages 25-44) and almost not at all among the elderly. Among the cases in the last week, 3.7% went to the emergency room, 1.2% were hospitalized and 0.1% died (42 people). Among the vaccinated, hospitalizations were 11% and 29% of the deaths were among vaccinated people. We do not know the personal profile of these people, which is very important to analyze these cases but we can say that, even if the number of vaccinated deaths seems large, normally this group of people would have represented about 85% of deaths and this suggests that the vaccines are working even against the Delta variant. From some calculations of age-specific hospital mortality rates in the British epidemic it is estimated that the link between hospitalization and death this time will be less than about one third.

The importance of the two doses

Based on the analysis of the English data, the vaccines in use in the UK (Pfizer and AstraZeneca) are still effective, especially after two doses, albeit to a slightly lesser extent. Experts have calculated 80 percent effectiveness after one dose towards the risk of hospitalization and death e greater than 95% after two doses. This data seems to be supported by the first neutralization studies of the Delta variant against the serum of vaccinated people. The weakest protection given by vaccines with people who received only one dose: in a study published in Lancet performed on 250 people vaccinated with Pfizer 79% of vaccinated with one dose had a neutralizing response of antibodies against Delta virus reduced to 32% (compared to the original strain) and 25% with the Beta variant (formerly South African). The cohort analyzed in the study had an average age of 40, was healthy and recently vaccinated. Immunity may be even lower in older or weaker people. The efficacy of the vaccine against Delta increased after 2 doses. Also a recent study on Nature confirms good protection after two doses, even if the Delta has one evasion capacity comparable to the South African variant, so far considered the worst.

June 13, 2021 (change June 13, 2021 | 17:11)



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