Cases of contagion and serious illness drop “substantially” with the third Pfizer dose. This is underlined by a study published in the New England Journal of Medicine, based on data from the Israeli health ministry. The infection rate, he notes, at least 12 days after the ‘booster’, is “11.3 times” lower than the two doses, while “the serious disease rate is 19.5” times lower. The study was conducted from July 30 to August 31 on 1.13 million over 60s who had completed immunization 5 months earlier, divided into two groups: those who received the third dose and those who received two.
Compared to the Delta variant, the study reads, the third Pfizer dose “would bring the efficacy of the vaccine among the subjects who received the booster to about 95%, a value similar to the efficacy of the original vaccine reported against the Alpha variant” .
In particular, 12 days after the booster dose, the confirmed infection rate was lower in the booster group than in the no booster group by a factor of 11.3; the severe disease rate was lower by a factor of 19.5. In a secondary analysis, the confirmed infection rate at least 12 days after vaccination was lower than the rate after 4-6 days by a factor of 5.4. According to the method followed by the researchers, data for the period from 30 July to 31 August 2021 were extracted from the Israeli Ministry of Health database, concerning 1,137,804 people aged 60 and over and who had been fully vaccinated. (i.e. they had received at least two doses of the Pfizer-BioNTech vaccine) 5 months earlier.
In the primary analysis, the confirmed Covid-19 rate and the severe disease rate were compared between those who had received a booster injection at least 12 days earlier (booster group) and those who had not received a booster injection. recall (non-booster group). In the secondary analysis, on the other hand, the infection rate 4 to 6 days after the booster dose was evaluated compared to the rate of at least 12 days after the booster. And the researchers concluded that rates of confirmed Covid-19 and severe disease were “substantially lower” among those who had received a booster (third) dose of the Pfizer vaccine. In the study they also explain that severe disease “was defined as a resting respiratory rate greater than 30 breaths per minute, an oxygen saturation of less than 94% when breathing ambient air, or a ratio of arterial oxygen partial pressure to fraction of inspired oxygen less than 300 ‘.