Recombinant bivalent vaccine protects against SARS-CoV-2 and influenza in animal models

In a recent study published in Virology JournalResearchers have developed a recombinant bivalent vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses.

Stady: VSV-based recombinant bivalent vaccine effectively protects against SARS-CoV-2 infection and influenza A. Image Credit: Studio Romantic / Shutterstock

The coronavirus 2019 (COVID-19) pandemic has posed a serious threat to global public health. Multiple vaccines have been used to prevent COVID-19, however, the emergence of highly contagious SARS-CoV-2 variants (VOCs) has jeopardized epidemic containment efforts. VOCs (SARS-CoV-2) cause vaccine penetration infection, thus challenging the efficacy of current COVID-19 vaccines and ensuring the development of improved vaccines.

Influenza is a contagious respiratory illness caused primarily by the influenza A virus (IAV). Seasonal influenza is a public health concern with more than 300,000 deaths annually. Influenza vaccines are the most effective means of preventing disease, but they are less effective (10% to 60%) due to differences between the vaccine strain and the circulating strains.

Hence, designing a universal vaccine against all strains of influenza is essential. Both influenza and COVID-19 are infectious diseases that are transmitted during the same seasons and pose a global threat to public health; As such, it is very useful to design a vaccine that concurrently protects against SARS-CoV-2 and influenza viruses.

Study and results

In this study, researchers built three bivalent vaccines based on recombinant vesicular stomatitis virus (rVSV) for COVID-19 and influenza. First, they generated coding DNAs (cDNAs) encoding a spike protein (SP) for SARS-CoV-2 Delta with a 17 amino acid (aa) deletion at the C-terminus and a point mutation (I742A) [henceforth, SPΔC1]. In addition, cDNAs encoding the S2 domain were generated by a 381 aa deletion (SPΔC2).

The receptor-binding domain (RBD) of the SARS-CoV-2 Wuhan-Hu-1 strain was combined with Ebola virus glycoprotein (GP) to generate the ERBD cDNA construct. Each of the three cDNAs was inserted into the rVSV-EM2e vaccine vector, which contains Ebola GP fused with four copies of an influenza M2 polypeptide (M2e) to generate V-EM2e/SPΔC1, V-EM2e/SPΔC2 or V-EM2e/ERBD.

Two copies of M2e were derived from human influenza strains, one from the avian influenza strain and the other from the swine influenza strain. The replication capacity of candidate vaccines was examined in multiple cell lines such as A549, MRC-5, U251MG, differentiation cluster 4 positive (CD4).+) Jurkat T cells and monocyte-derived macrophages (MDMs) and dendritic cells (MDDCs).

Although wild-type VSV showed efficient replication and typical cytopathic effects (CPEs) in different cell lines, rVSV candidates failed to infect MRC-5 and CD4.+ Jurkat T cells. The candidate vaccine showed positive infection in other cell types and replicated much more slowly with lower CPE than wild-type VSV. Two doses of each candidate vaccine were administered on days 0 and 14 in BALB/c mice by intramuscular (IM) or intranasal (IN) injection.

Antibodies were measured in serum anti-SARS-CoV-2 RBD and anti-M2 antibodies. They found higher levels of SARS-CoV-2 IgA and IgG antibodies with candidates V-EM2e/SPΔC1 and V-EM2e/SPΔC2 with IM administration than with IN delivery. V-EM2e/ERBD immunization via the IM pathway produced significantly fewer IgG antibodies than the two other candidate vaccines.

All candidates elicited similarly high antibodies to M2 IgG and IgA regardless of the delivery route. Next, they evaluated the antibody-neutralizing efficacy of vaccine candidates using SPΔC pseudoviruses. V-EM2e/SPΔC1 vaccine induced the highest titer of neutralizing antibodies (nAbs) against SpΔCwild type and SpΔCDelta pseudoviral infection, whereas V-EM2e/ERBD immunization had low neutralizing activity.

Then, splenocytes from control and immunized mice without (any) peptides were cultured, pooled with interfering peptide S1 or influenza M2e peptides. Stimulation of mouse IN-immunized spleen cells with S1 or M2e peptides increased the secretion of interferon-gamma (IFN-γ) and, to a lesser extent, interleukin (IL)-4 compared to controls. However, IL-5 production was not stimulated by S1 or M2e peptides.

In intramuscularly immunized mouse spleen cells, elevated cytokine levels were evident before and remained unchanged after stimulation. Besides, mice immunized with V-EM2e/SPΔC1 were immunized intramuscularly or within the pathway and challenged with a lethal dose of H1N1 or H3N2 influenza strain on day 28. Control mice showed higher morbidity than immunized mice and lost >20% of weight for five days. / Six days.

In contrast, vaccinated mice showed a moderate weight loss, with a 100% survival rate regardless of the method of vaccination. Finally, the authors investigated the protective effect of V-EM2e/SPΔC1 and V-EM2e/SPΔC2 immunization in Syrian hamsters against SARS-CoV-2 infection. The team noted that a single intramuscular dose of either vaccine was sufficient to elicit the peak anti-elevation IgG antibody titer.

Hamsters were challenged with SARS-CoV-2 Delta 14 days after administration of the second vaccine dose. Control (unvaccinated) hamsters showed weight loss after infection and recovered by 12th day. The vaccinated animals showed marginal weight loss and began to recover after 2 days. Oral swabs collected on the third day showed a significant decrease in viral RNA levels in the vaccinated animals.


In summary, among the three bivalent candidate vaccines, V-EM2e/SPΔC1 and V-EM2e/SPΔC2 induced potent nAbs, humoral and cellular responses, protected mice/hamsters against influenza (H1N1 and H3N2) and SARS-CoV-2 Delta infection. Taken together, the results provided substantial evidence of the excellent efficacy of a bivalent vaccine platform that can be accelerated to create vaccines against novel or renewable variants of SARS-CoV-2 and IAV infection.