Several variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have emerged since the virus was first identified in late December 2019.
Study: Serum neutralization of SARS-CoV-2 Omicron BA.1 and BA.2 after booster vaccination BNT162b2. Image Credit: Thannaree Deepul / Shutterstock.com
More recently, SARS-CoV-2 Omicron variant BA.1 (B.1.1.529) emerged in late 2021 and was promptly designated as a variant of concern (VOC) in November 2021 by the World Health Organization (WHO). ) as a result of its numerous mutations in its spike (S) protein and its notable vaccine escape properties. Epidemiological studies have demonstrated that two doses of vaccines against coronavirus disease 2019 (COVID-19), together with a booster dose of a messenger ribonucleic acid (mRNA) vaccine, confer temporary protection against Omicron BA.1 .
Several countries where BA.1 was initially detected reported that the Omicron BA.1 lineage was quickly replaced by the Omicron BA.2 sublineage. To date, the Omicron BA.2 variant is the current dominant circulating strain of SARS-CoV-2, accounting for nearly 86% of all new sequence cases.
The United States, for example, recently reported a weekly doubling of cases with the BA.2 subline. The increased infection rates and transmissibility in countries with high vaccination rates indicate that the BA.2 subline harbors a more potent vaccine escape mechanism than the Omicron BA.1 line.
About the study
A recent CDC Emerging infectious diseases the study investigates the Omicron BA.2 subline for its vaccine escape abilities by comparing the neutralization of the BA.1 and BA.2 strains in samples from immunized individuals who had received two doses and a booster dose of the Pfizer-BioNTech BNT162b2 mRNA vaccine. All samples were collected between January 26, 2022 and January 28, 2022.
Serum samples were analyzed with a 90% plaque reduction neutralization assay (PRNT90 ). Clinical isolates for PRNT90 were identified by whole genome sequencing, which provided information on lineage and mutation calls in the samples. The samples were also analyzed for the presence of neutralizing antibodies using the Quantitative Immunoglobulin g (IgG) Binding TrimericS immunoassay.
The study cohort consists of 20 immunocompetent participants, including 12 women and eight men, with no history of prior SARS-CoV-2 infection. The median age of the participants was 57 years old.
The median time between the two mRNA vaccine doses was 35 days, while the median time between the second dose and the booster dose was 168 days. The median time between booster dose and sample collection was 42 days.
Neutralization titers in serum samples exceeded the threshold limit for Omicron BA.1 and BA.2 sublines. Statistically significant differences were reported between the neutralization titers of BA.1 and BA.2 compared to the ancestral strain; however, the difference in neutralization titers was insignificant between BA.1 and BA.2.
Vaccine evasion appears to be the main mechanism contributing to the higher transmissibility of the Omicron BA.1 and BA.2 subline. Nevertheless, BA.2 was not able to evade BNT162b2 vaccine-induced humoral immunity better than BA.1.
It was thus inferred that the Omicron BA.2 sublineage has divergent modes of transmissibility other than vaccine-induced antibody leakage that have contributed to the current upsurge in BA.2 infections.
PRNT results90 of serum against the ancestral SARS-CoV-2 strain and the Omicron BA.1 and BA.2 sublines after BNT162b2 (Pfizer-BioNTech, https://www.pfizer.com) booster vaccination, Denmark. Serum samples were collected from 20 naïve SARS-CoV-2 participants who received 2 doses of BNT162b2 and a booster dose of BNT162b2. The sequences of the viral genome are available in GenBank (accession numbers ON055855 for the ancestral strain, ON055874 for BA.1 and ON055857 for BA.2). The red line indicates the neutralization threshold; black lines indicate median neutralization titers for each strain. PRNT9090% plaque reduction neutralization test.
The neutralization of the Omicron BA.1 line and the BA.2 subline is equal, as their neutralization abilities appear to be nearly eight times lower than that of the ancestral strain of SARS-CoV-2. The neutralization cut-off value for BA.1 and BA.2 six weeks after a booster vaccination indicated at least transient protection conferred by the vaccine against mild infection by the BA.2 sublineage.
Taken together, the results of the current study underscore the importance of booster vaccination after two prior doses of COVID-19 vaccine, as it confers protection against Omicron BA.1 and BA.2 strains.
- Pedersen, RM, Bang, LL, Madsen, LW, et al. (2022). Serum neutralization of SARS-CoV-2 Omicron BA.1 and BA.2 after booster vaccination BNT162b2. United States Centers for Disease Control and Prevention Emerging Infectious Diseases. doi:10.3201/eid2806.220503.