Recombinant measles virus encoding the spike protein of SARS-CoV-2 efficiently induces Th1 responses and neutralizing antibodies that block SARS-CoV-2 variants.

Owing to the rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants, the development of effective and safe vaccines has become a priority. The measles virus (MeV) vaccine is an attractive vaccine platform as it has been administered to children for more than 40 years in over 100 countries. In this study, we developed a recombinant MeV expressing the full-length SARS-CoV-2 spike protein (rMeV-S) and tested its efficacy using mouse and hamster models. In hCD46Tg mice, two-dose rMeV-S vaccination induced higher Th1 secretion and humoral responses than one-dose vaccination. Interestingly, neutralizing antibodies induced by one-dose and two-dose rMeV-S immunization effectively blocked the entry of the α, ß, γ, and δ variants of SARS-CoV-2. Furthermore, two-dose rMeV-S immunization provided complete protection against SARS-CoV-2 in the hamster model. These results suggest the potential of rMeV-S as a vaccine candidate for targeting SARS-CoV-2 and its variants.

Immunogenicity of candidate SARS-CoV-2 DNA vaccines based on the spike protein.

Coronavirus disease 2019 caused by the novel human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently a major threat to public health worldwide. To deal with the needs of vaccine, we developed four DNA vaccine candidates against SARS-CoV-2, based on the full-length spike (S) or truncated S protein. Following mice vaccination, we measured T-cell response and antigen-specific neutralizing antibody (NAb) titer. All four candidates induced humoral immune responses, including elevated levels of total IgG and NAbs, and cell-mediated immune responses, including multiple cytokine expression. However, the full-length S DNA vaccine enhanced the immune responses most significantly. We then evaluated its appropriate antigen dose and vaccination schedule. Although all immunized groups showed higher immune response than the control group, inoculation with 50 µg antigen led to the highest NAb titer. Immunity was significantly increased after the third inoculation. Thus, the full-length S DNA vaccine can potentially prevent SARS-CoV-2 infection.