Hybrid immunity from prior omicron infection, vaccination provides best COVID-19 protection
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Hybrid immunity from prior omicron infection and at least two doses of COVID-19 vaccine provided the highest protection from omicron infection, according to data recently published in The Lancet.
“In the context of a high proportion of Quebec’s and world’s population already vaccinated with at least two vaccine doses, omicron demonstrated to escape both natural (conferred by a previous infection) and vaccine (conferred by vaccination) immunity,” Sara Carazo, MD PhD, member of biological risks unit of the Institut National de Santé Publique du Québec, told Healio. “While omicron waves associated with different subvariants continue to occur, it was clear the need to better understand who and till which extent will be protected against newly circulating subvariants of omicron (BA.2).”
Carazo and colleagues conducted a test-negative case-control study among health care workers aged 18 years and older who were tested for SARS-CoV-2 in Quebec between March 27 and June 4, 2022, when BA.2 was the predominant variant. According to the study, the researchers identified cases — positive test during study period — and controls — negative test during study period — using the provincial laboratory database that records all nucleic acid amplification testing for SARS-CoV-2 in Quebec.
They then used the provincial immunization registry to determine vaccination status. Logistic regression models were used to compare the likelihood of BA.2 infection or reinfection — a second positive test 30 days or more after primary infection — among health care workers who had previous primary infection and none to three doses of messenger RNA vaccine vs. those who were unvaccinated with no primary infection.
In total, 258,007 SARS-CoV-2 tests were conducted during the study period. Among those with a result and patients that met the inclusion criteria, there were 37,732 presumed BA.2 cases (2,521 reinfections following pre-omicron primary infection and 659 reinfections following BA.1 primary infection) and 73,507 controls (7,360 with pre-omicron primary infection and 12,315 with BA.1 primary infection).
They found that, overall, pre-omicron primary infection was associated with a 38% (95% CI, 19-53) reduction in BA.2 infection risk, with higher BA.2 protection among those who had also received one (56%; 95% CI, 47-63), two (69%; 95% CI, 64-73) or three (70%; 95% CI, 66-74) mRNA vaccine doses.
Additionally, data showed that omicron BA.1 primary infection was associated with greater protection against BA.2 infection (risk reduction = 72%; 95% CI, 65-78), and protection was increased further among those who had received two doses of mRNA vaccine (risk reduction = 96%; 95% CI, 95-96) but was not improved with a third dose (96%; 95% CI, 95-97).
Carazo concluded that this hybrid immunity provided “very high” protection against BA.2 omicron, although it was not improved with additional doses. She added that longer follow-up and studies of protection against BA.5 and new subvariants are needed to continue guiding public health stakeholders and immunization programs.
“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 populations with high frequencies of vaccination and BA.1 or BA.2 infection,” David S. Hui, BBS, JP, faculty of medicine at the Chinese University of Hong Kong, wrote in an accompanying commentary.
He added that second-generation BA.4- or BA.5-based vaccines should be considered for managing the widely circulating BA.5 variant.
Carazo S, et al. Lancet. 2022;doi:10.1016/S1473-3099(22)00578-3.
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