This is a summary, written by members of the CITF Secretariat, of:

Lin YJ, Evans DH, Robbins NF, Orjuela G, Abe KT, Rathod B, Colwill K, Gingras AC, Tuite A, Yi QL, O’Brien SF, Drews SJ. Diminished Neutralization Capacity of SARS-CoV-2 Omicron BA.1 in Donor Plasma Collected from January to March 2021. Microbiol Spectr. 2023 Jun 8:e0525622. doi: 10.1128/spectrum.05256-22.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in Microbiology Spectrum, found that vaccinated donors, regardless of infection status, were more likely than unvaccinated donors to neutralize Omicron when assessed by a plaque reduction neutralization (PRNT50)Plaque reduction neutralization assays are used to assess the neutralization capacity of donor plasma against wild-type SARS-CoV-2 and SARS-CoV-2 variants of concern. assay. The study was led by Dr. Steven Drews, in collaboration with Dr. Sheila O’Brien, both from Canadian Blood Services.

Samples were collected from January to March 2021. For PRNT50 studies, plasma samples previously analyzed for neutralizing antibodies against wild-type, Alpha, Beta, Delta, and Gamma variants were used. All had evidence of an anti-S or anti-receptor binding domain (RBD) signal (with or without anti-N). Among 25 samples from vaccinated individuals, 5 showed signals for anti-N antibodies. Among 39 samples from unvaccinated individuals, 19 had anti-N signals.

Additionally, 4,390 specimens (randomly sampled, regardless of serological evidence of infection) were also tested for anti-SARS-CoV-2 binding antibodies quantification.

Key findings:

When tested for ability to neutralise Omicron SARS-CoV-2, plasma collected from vaccinated Canadian blood donors was more likely to have measurable neutralizing antibodies (measured by PRNT50) than plasma from unvaccinated blood donors. In the vaccinated vs. unvaccinated group, the percentages of samples with any measurable PRNT50 were:

SARS-CoV-2 variants No. of samples showing neutralization in the vaccinated group (%) No. of samples showing neutralization in the unvaccinated group (%)
Wild-type/Ancestral 21/25 (84%) 16/39 (41%)
Alpha 19/25 (76%) 16/39 (41%)
Beta 18/25 (72%) 10/39 (26%)
Gamma 13/25 (52%) 9/39 (23%)
Delta 19/25 (76%) 16/39 (41%)
Omicron BA.1 9/25 (36%) 0/39 (0%)

For Omicron (BA.1) neutralization, the results for vaccinated (9/25 [36%]) versus unvaccinated (0/39) were highly significant (P<0.0001).

None of the 4,453 samples collected had an antibody binding capacity (≥2 × 104 binding antibody units/mL [BAU/mL]), a high titer of binding antibodies suggestive of a better neutralizing capacity against Omicron BA.1.

Overall, the data from this study suggest that even in populations with high rates of SARS-CoV-2 infection, vaccination (including additional doses with monovalent or bivalent vaccines) is an important strategy to reduce the burden of severe disease and death.