COVID-19 Scan for Sep 22, 2022

Study shows previous Omicron infection most protective against BA.2A study in The Lancet Infectious Diseases demonstrates that previous Omicron BA.1 infection was the most protective factor against BA.2 infection (associated with a risk reduction of 72%) and gave greater protection than primary infection with pre-Omicron SARS-CoV-2 (38%) or three doses of an mRNA vaccine in people with no previous infection (46%).The test-negative case-control study involved Quebec healthcare workers to compare those who had a positive SARS-CoV-2 test during the period of Omicron BA.2 dominance, from Mar 27 to Jun 4, 2022, with healthcare workers who had a negative test during the same period.The primary COVID-19 infection had to take place at least 30 days before the study period, with pre-Omicron infections occurring between Feb 20, 2020, and Nov 27, 2021.

Omicron BA.1 attribution was given for all cases between Dec 26, 2021, and Mar 26, 2022. In total, 37,732 presumed Omicron BA.2 cases were compared with 73,507 randomly selected controls.The authors said that among cases, 1,159 (3.1%) had a primary infection combined with two mRNA vaccine doses, and 1,436 (3.8%) had a primary infection and three vaccine doses.

Among controls, 687 (10.9%) had a primary infection combined with two vaccine doses, and 821 (13.4%) had a primary infection and three vaccine doses.Hybrid immunity from BA.1 infection plus two or three mRNA vaccine doses increased effectiveness to 96% for longer than 5 months.

Notably, a third vaccine dose conferred no improvement to that hybrid protection."These data provide immunological context for the importance of hybrid immunity in managing the current surges caused by the BA.2.12.1, BA.4, and BA.5 subvariants in