In a new study, researchers found that a leading candidate COVID-19 vaccine raised neutralizing antibodies and robustly protected non-human primates against SARS-CoV-2, the virus that causes COVID-19.
This vaccine led to robust protection against SARS-CoV-2 in rhesus macaques and is now being evaluated in humans.
The research was conducted by a team at Beth Israel Deaconess Medical Center and elsewhere.
The development of a safe and effective vaccine will likely be required to end the COVID-19 pandemic.
The new vaccine (Ad26.COV2.S) uses a common cold virus, called adenovirus serotype 26 (Ad26), to deliver the SARS-CoV-2 spike protein into host cells, where it stimulates the body to raise immune responses against the coronavirus.
The team has been working on the development of a COVID-19 vaccine since January when Chinese scientists released the SARS-CoV-2 genome.
The researchers, in collaboration with Johnson & Johnson, developed a series of vaccine candidates designed to express different variants of the SARS-CoV-2 spike protein, which is the major target for neutralizing antibodies.
In the study, the team conducted a study in 52 animals, immunizing 32 adult rhesus macaques with a single dose of one of seven different versions of the Ad26-based vaccine, and giving 20 animals sham vaccines as placebo controls.
All vaccinated animals developed neutralizing antibodies following immunization.
Six weeks after the immunization, all animals were exposed to SARS-CoV-2. All 20 animals that received the sham vaccine became infected and showed high levels of virus in their lungs and nasal swabs.
Of the six animals that received the optimal vaccine candidate, none showed the virus in their lungs, and only one animal showed low levels of virus in nasal swabs.
Moreover, neutralizing antibody responses correlated with protection, suggesting that this biomarker will be useful in the clinical development of COVID-19 vaccines for use in humans.
The findings show that a single immunization with Ad26.COV2.S robustly protected rhesus macaques against SARS-CoV-2 challenge.
A single-shot immunization has practical and logistical advantages over a two-shot regimen for global deployment and pandemic control, but a two-shot vaccine will likely be more immunogenic, and thus both regimens are being evaluated in clinical trials.
The researchers look forward to the results of the clinical trials that will determine the safety and immunogenicity, and ultimately the efficacy, of the Ad26.COV2.S vaccine in humans.
Pending clinical trial outcomes, the Ad26.COV2.S vaccine is on track to start a phase 3 efficacy trial in 30,000 participants in September.
One author of the study is immunologist Dan H. Barouch, MD, Ph.D.
The study is published in Nature.
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