Finding an effective vaccine is crucial to stemming the spread of coronavirus disease (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pathogen.
Researchers at the School of Medicine, Washington University in Saint Louis, USA, showed that the intranasal route of immunization could provide a more efficient protection against SARS-CoV-2 compared to the intramuscular route (i.e. through ‘jabs’).
The study compared the protective capacity of intranasal and intramuscular delivery of a chimpanzee adenovirus-vectored vaccine encoding a pre-fusion stabilized spike protein (ChAd-SARS-CoV-2-S) in Golden Syrian hamsters.
The race of a COVID-19 vaccine
In December 2019, a mysterious pneumonia-like illness spread in Wuhan City, China. From there, more than 191 countries and territories have been affected. To date, there are over 67.11 million cases and more than 1.53 million deaths globally.
The United States reports the highest number of cases, reaching more than 14.76 million, followed by India, with over 9.67 million cases, and Brazil, with more than 6.6 million cases. Many countries report surging cases after lockdown measures were lifted in an attempt to boost the economy, which has been negatively impacted by the pandemic’s disruption.
Scientists identified the causative agent SARS-CoV-2 by January 2020, and scientists started to develop vaccines to contain the virus spread. According to the World Health Organization (WHO), more than 200 candidate vaccines have been developed against COVID-19.
Of the candidate vaccines under clinical evaluation, 13 are now in the last stage of human trials. If these vaccines pass the Food and Drug Administration (FDA) standards and other regulatory bodies, vaccines may be available to the public by 2021.
In the UK, a mRNA vaccine candidate has received regulatory approval and is in the process of being rolled out to targeted demographics vulnerable to severe disease or continual exposure (those with underlying health conditions, frontline healthcare workers and the elderly).
The study, published in the pre-print journal bioRxiv*, used the SARS-CoV-2 hamster model, which has been used to study the effectiveness of several drugs and candidate vaccines.
The researchers tested the efficacy of a chimpanzee adenovirus (ChAd)-vectored vaccine expression a perfusion-stabilized version of the S protein of SARS-CoV-2 (ChAd-SARS-CoV-2-s) in Syrian hamsters following intramuscular or intranasal delivery.
The team has found that a single dose of the vaccine induced a robust S protein-specific antibody response, which can neutralize SARS-CoV-2. However, the team revealed that when the vaccine was administered intranasally, it triggered six-fold higher antibody titers than intramuscular delivery.
The team further showed that the immunized hamsters had less infectious viruses and viral RNA in the lungs and nasal swabs. This was also tied to a reduced illness and numbers of viral-infected cells in the lungs.
The researchers also noted reduced weight loss, disease, and inflammatory gene expression in the animals' lungs who received the vaccine. The intranasal administration of the vaccine protected the upper respiratory tract of the animal models, while the intramuscular vaccine did not.
The study demonstrates that a single dose of the vaccine delivered intranasally provides better protection than intramuscular administration against SARS-CoV-2.
"Overall, our studies in hamsters demonstrate that IN delivery of the ChAd-SARS-CoV-2-S vaccine confers protection against SARS-CoV-2 challenge. Protection is associated with lower virus levels in the lungs and upper and lower respiratory tracts, no weight loss, and reduced inflammation in the lungs," the researchers concluded in the study.
"These findings support further pre-clinical and clinical studies investigating the vaccine efficacy of IN delivered vaccines against SARS-CoV-2," they added.
The intranasal administration of the vaccine offers many benefits over traditional approaches. First, it provides a less invasive administration without needles. Next, intranasal vaccination is linked to mucosal immune responses.
To date, influenza virus vaccines are the only licensed intranasal vaccines for people over the age of 2 and less than 50 years old.
Though the vaccine shows promise in fighting the virus, human trials are still needed to determine its efficacy and safety. It will go through rigorous tests and trials before it gets approved by regulatory agencies for public use.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Bricker, T., Darling, T., Hassan, A., Harastani, H., Soung, A. et al. (2020) A single intranasal or intramuscular immunization with chimpanzee adenovirus vectored SARS-CoV-2 vaccine protects against pneumonia in hamsters. bioRxiv. doi: https://doi.org/10.1101/2020.12.02.408575, https://www.biorxiv.org/content/10.1101/2020.12.02.408823v1