The COVID-19 pandemic has wreaked havoc around the world, leading to significant social and economic impacts. The development of effective vaccines has brought hope for ending the pandemic. A single-dose novel live-attenuated intranasal SARS-CoV-2 vaccine candidate has been shown to elicit both protective mucosal and systemic immunity. This new vaccine approach may offer a powerful and practical solution to the COVID-19 pandemic. In this article, we explore the potential of this vaccine candidate to combat the pandemic and discuss the implications of this new vaccine technology.
A new study posted on the bioRxiv preprint server examines the protective immunity provided by a single dose of a live-attenuated SARS-CoV-2 vaccine candidate. This vaccine was given intranasally to K18-human angiotensin-converting enzyme 2 (hACE2) mice, and the results were compared to mice given either wildtype virus (WT) or a phosphate-buffered saline (PBS) inoculation. At 28 days post-vaccination, blood, lung, spleen, and bronchoalveolar lavage (BAL) samples were taken to assess immune responses. The efficacy of the vaccine was assessed by exposing the mice to a SARS-CoV-2 WT strain virus, the Omicron BA.5 subvariant of the virus, or a PBS control.
Results showed that none of the mice given the single-dose vaccine or the PBS inoculation exhibited clinical symptoms or weight loss, while 7.6% of the WT-infected mice died within seven to 12 days of infection. Lung samples from both WT and vaccine-infected mice showed that both had a Th1-prone immune reaction. However, CD4+ T cells had higher or comparable production of interferon (IFN+) in the vaccine cohort. Results of the study also showed that WT and vaccine strains showed comparative percentages of Th1-prone immune response in the spleen. RBD-specific immunoglobulin (Ig)-A+ B cell responses elicited in WT and vaccine strains were comparable, but vaccine strains showed a 25% lower response. SARS-CoV-2-specific IgA or IgG antibody levels in BAL fluid samples showed no significant differences between the two cohorts.
Interestingly, none of the vaccine-infected mice exhibited detectable viral loads in their trachea or lungs two days after challenge. Conversely, the PBS-inoculated mice showed viral loads of over 106 PFU/g lung tissue. Subsequent observations show that WT or vaccine-inoculated mice survived infection, while four of the nine PBS-vaccinated animals died between seven to nine days after a virus challenge.
The study concludes that intranasal vaccination with the live-attenuated SARS-CoV-2 vaccine candidate shows high efficacy in protecting K18-hACE2 mice from SARS-CoV-2 challenge. It promotes potent and functional activation of pulmonary cells and induces strong immune responses in the systemic and mucosal compartments. Thanks to these promising results, the researchers hope that the Delta 3678 virus can serve as an effective vaccine candidate for future immunizations, leading to improved and more robust immunity against the virus.
In conclusion, the development of a single-dose novel live-attenuated intranasal SARS-CoV-2 vaccine candidate has shown promising results in providing both protective mucosal and systemic immunity. The potential of this vaccine candidate could offer a significant advantage over current vaccine options by providing protection in both the upper and lower respiratory tracts. As we continue to fight against the COVID-19 pandemic, the development and delivery of effective vaccines remain a crucial component in ending the spread of the virus. The successful development and distribution of this vaccine candidate could provide a valuable tool in achieving this goal.
