Immunogenicity of monovalent and multivalent subunit vaccines against SARS-CoV-2 variants in mice with divergent vaccination history

Abstract

There are challenges in selecting SARS-CoV-2 vaccine compositions, primarily due to divergent infection or vaccination history and immunological biases toward previous strains. In this study, we evaluated humoral immune responses induced by variant-based monovalent vaccines as booster shots in mice previously vaccinated with an ancestral strain-based vaccine with or without Omicron BA.5 exposure. Our data suggest that immunological biases toward earlier variants attenuated the potency of variant-based vaccines as a booster dose against subsequent variants, whereas a second booster dose mitigated this effect. Furthermore, in the context of vaccine-induced immunity, prior exposure to Omicron sublineages (e.g., BA.5) attenuated the effect of immunological biases toward earlier variants on the neutralizing potency against Omicron subvariants. In addition, the interval between vaccine doses should also be considered, as an immunologic plateau might occur after repeated vaccination. Furthermore, the XBB.1 monovalent vaccine and a tetravalent vaccine (SCTV01E-2) composed of pre-Omicron variant (Beta) and Omicron subvariants (BA.1, BQ.1.1, and XBB.1) showed comparable neutralizing potency against several Omicron sublineages (BA.1, BA.5, BQ.1.1, XBB.1, XBB.1.5, XBB.1.16, and EG.5) under divergent vaccination history, implicating that multivalent platforms could be explored as a flexible strategy if future strains diverge significantly from current variants.IMPORTANCEContinuous evolution of SARS-CoV-2 variants has raised the need to optimize immunization regimens and update vaccine compositions to protect against the newly emerging variants in the context of repeated vaccination. The significance of this research is briefly summarized as follows:1) Immunological biases toward earlier variants attenuated the potency of variant-based vaccines as a booster dose against subsequent variants, which can be mitigated by a second booster dose.2) In the context of vaccine-induced immunity, a previous exposure to Omicron sublineages, such as BA.5, attenuated the influence of immunological biases toward earlier variants on the neutralizing potency against Omicron subvariants.3) The interval between vaccine doses should be taken into account since an immunologic plateau might occur after repeated vaccination.4) Multivalent vaccines, with epitope diversity, may theoretically enhance the magnitude and breadth of cross-neutralization responses, thereby providing a buffer for unpredictable future variants.

Keywords: SARS-CoV-2; monovalent vaccines; multivalent vaccines; vaccine-induced immunity.

Fig 1

Neutralizing antibody responses of monovalent vaccines as one- or two-dose booster shots following priming series against the ancestral strain and Omicron subvariants in mice. (A) Schematic of the immunization design. Mice were intramuscularly administered two doses of D614G monovalent vaccine on Day 0 and Day 14. After 4 and 6 months, the monovalent vaccines (Beta, BA.5, BQ.1.1, or XBB.1) were injected into mice as one or two doses of booster shots. Serum neutralizing titers against PsV displaying D614G (B), Beta (C), BA.5 (D), BQ.1.1 (E), and XBB.1 (F) were measured. P values and fold change of neutralization were annotated above each bar, and geometric mean titers (GMTs) were labeled in the corresponding columns. Data were represented as mean ± SD, n = 5-6/group. Due to limited serum availability, 5 mice were included for the assessment of BQ.1.1 neutralization. Neutralizing capacity of monovalent vaccines based on pre-Omicron variant (Beta) or Omicron sublineages (BA.5, BQ.1.1, or XBB.1) as booster doses following ancestral strain-based primary series with or without subsequent BA.5 exposure.

Fig 2

Humoral immune responses induced by boosting with a single-dose monovalent vaccine following priming series with or without BA.5 exposure in mice. (A) Schematic of the immunization design. Mice were intramuscularly administered two doses of D614G monovalent vaccine on Day 0 and Day 14. After 4 months, the monovalent vaccines (Beta, BA.5, BQ.1.1, or XBB.1) were injected into mice as a booster shot. Another group of priming mice was immunized with the BA.5-based vaccine, mimicking infection or vaccination with the BA.5 variant at 3 months and received a single booster shot with monovalent vaccines 1 month later. Serum neutralizing titers against PsV displaying D614G (B), Beta (C), BA.5 (D), BQ.1.1 (E), and XBB.1 (F). P values and fold change of neutralization were annotated above each bar, and geometric mean titers (GMTs) were labeled in the corresponding columns. Data were represented as mean ± SD, n = 6/group.

Fig 3

Neutralizing titers induced by boosting with one or two doses of monovalent vaccines following priming series and BA.5 exposure in BALB/c mice. (A) Schematic of the immunization design. Mice were intramuscularly administered two doses of the D614G monovalent vaccine as primary immunization over a 2-week interval. 3 months later, primed mice were immunized with BA.5-based vaccine, mimicking infection or vaccination with the BA.5 variant, and were boosted with one or two doses of monovalent vaccines at 1 and 2 months, respectively. Serum samples were collected at 2 weeks after the last vaccination for neutralization assays. Neutralizing activities against PsV displaying D614G (B), Beta (C), BA.5 (D), BQ.1.1 (E), and XBB.1 (F). P values and fold change of neutralization were annotated above each bar, and geometric mean titers (GMTs) were labeled in the corresponding columns. Data were represented as mean ± SD, n = 6/group.

Fig 4

Neutralization capacities induced by a single booster dose of SCTV01E-2, or XBB.1 monovalent vaccines following priming series and BA.5 exposure in mice. (A) Schematic of the immunization design. Mice were intramuscularly administered two doses of the D614G monovalent vaccine as primary immunization over a 2-week interval. After 2 months, mice were immunized with the BA.5 vaccine (mimicking infection or vaccination with the BA.5 variant) and administered a single dose of XBB.1 monovalent vaccine or SCTV01E-2 1 month later. Serum samples were collected at 2 weeks, 2 months, or 4 months after the last vaccination for neutralization assays. (B–D) Neutralizing activity 2 weeks (B), 2 months (C), and 4 months (D) after the booster shot. P values and fold change of neutralization were annotated above each bar, and geometric mean titers (GMTs) were labeled in the corresponding columns. Data were represented as mean ± SD, n = 5-6/group.

Fig 5

Neutralization capacities induced by a single dose of SCTV01E-2 or XBB.1 monovalent vaccine in mice with prior exposure to several previous dominant SARS-CoV-2 variants. (A) Schematic of the immunization design. Balb/c mice were intramuscularly administered one dose of the D614G vaccine (1 µg/dose). Two weeks later, a vaccine composed of S-Trimer of Beta, BA.1, BQ.1.1, XBB.1 (1 μg/dose) mimicking infection or vaccination with various dominant SARS-CoV-2 variants. Mice were subjected to a single dose of either XBB.1 monovalent vaccine or SCTV01E-2 one month later. Serum samples were collected 7 days later to measure the neutralizing titers. (B) Neutralizing activities against PsV displaying JN.1, KP.2, KP.1.1, and JN.1.11.1. P values and fold change of neutralization were annotated above each bar, and geometric mean titers (GMTs) were labeled in the corresponding columns. Data were represented as mean ± SD, n = 6-7/group.

Fig 6

Correlation between pseudovirus and live virus neutralization activity of immune sera from C57BL/6 mice. Correlation analysis between serum neutralizing capability against live virus and pseudovirus of BA.2 (A), BA.5 (B), and XBB.1 (C) variants.