New study (which includes the Delta variant): the drop in protection against infections by 40%, but protection against serious disease remains very high for months, at 93%
Decline in the prevention of infections
The study based on 3.4 million patients (over 12 years old) of the Kaiser Permanente Southern California Hospital Consortium. The data covered fully vaccinated individuals between December 2020 and July 2021, and Pfizer funded the research. The primary analysis calculated the risk of infection by comparing unvaccinated individuals with fully vaccinated individuals for each calendar day. The researchers investigated the protection of the vaccine in the presence of the different variants that occurred in the US in that period and separated and adjusted the data. Without Delta variant, vaccine efficacy against infection decreased over time, down by almost 30%: it was 97% at the beginning and dropped to 67% after 4 months, but the effectiveness against hospitalizations (over 90%) did not decline.
Delta data
The researchers sequenced the positive samples to evaluate the presence of variants and the individual months: in the California region Epsilon dominated in winter, Alpha in the spring and Delta in the summer. The study examined the data relating to the Delta variant which are the most significant at this time, given that the Delta is now prevalent in the world (and in Italy, of course).
Vaccine efficacy against Delta variant infections was elevated during the first month after full vaccination al 93% [95% CI 85-97], ma dropped to 53% [39-65] after 4 months. The decline does not appear to be attributable to Delta, because the waning effect is seen with all the variants. The good news remains high protection against hospitalization: with an initial average effectiveness 93%, which, even in the presence of Delta, showed no signs of diminishing after 3-4 months.
October 5, 2021 (change October 5, 2021 | 17:28)
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