![]() For the neutralization studies, results were divided into two sections: an analysis of differences in the levels of immune response markers post Omicron by individual vaccination and/or prior infection status and a comparison of the differences in level of neutralization of the different Omicron sublineages and other VOCs post Omicron infection. Twenty-three studies were identified, including six observational studies on the risk of reinfection and 17 in vitro studies on the kinetics and durability of neutralizing antibodies and memory immune response markers (B-cell and T-cell) post infection with any of the Omicron sublineages. Studies on animal models of immunity post Omicron were excluded. Instead, immune markers indicate that the immune system is primed to respond to a pathogen, which may result in prevention of infection or reduced morbidity. However, it is important to note that markers of protective immunity do not necessarily or directly equate to protection. The risk of reinfection and level of immune markers measured as neutralizing antibodies and cellular immunity activity against a pathogen can be indicative of protective immunity. Reinfection is defined as a previous confirmed and resolved SARS-CoV-2 case that has a subsequent infection of SARS-CoV-2 and it is confirmed as two different infections by laboratory evidence Footnote 3. Hybrid immunity refers to immunity that comes from both vaccination with one or more doses of a COVID-19 vaccine and immunity via infection with SARS-CoV-2 before or after vaccination Footnote 2. The different immune profiles as defined by the World Health Organization (WHO), include infection-induced immunity, vaccine-induced immunity and hybrid immunity. In this rapid review, real world data on reinfections post Omicron infection and post-Omicron immunogenicity studies (e.g., neutralizing/binding antibodies and memory immune markers such as T-cells and B-cells) are summarized across the different profiles of pre-Omicron immunity (vaccination and/or infection) studied. Omicron's ability to escape neutralizing antibodies that would stop the virus from entering and replicating in cells is due to the many mutations on the S-protein, particularly in key spots on the receptor binding domain (RBD) Footnote 1.Īlthough the literature on vaccine efficacy, role of waning immunity post vaccination, and/or previous infection with earlier variants is well established, little is known about immunity post Omicron infection. Compared to previous variants, Omicron has a large number of mutations (>30 mutations in the spike (S) protein) - and thus, has been good at evading established immunity from prior infection or vaccination Footnote 1. Omicron has evolved into multiple sublineages such as BA.1, BA.2, BA.3, BA.4, and BA.5, each with additional mutations. ![]() The SARS-CoV-2 variant of concern (VOC) Omicron (B.1.1.529) emerged in late 2021 and quickly displaced the Delta variant. What do we know about protective immunity post Omicron infection (against Omicron/other variants of concern?) ![]()
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