Just after biotech company Moderna recently announced the success of its first phase of the mRNA COVID-19 vaccine, two more promising candidate vaccines are sending encouraging news to the public that several vaccines are competing to enter phase II human trials,media reported. A new article in The Lancet presents peer review and published data for the first phase of a clinical trial of a new coronary pneumonia (COVID-19) vaccine.
It is understood that the main purpose of the first phase of the vaccine trial is to study the safety of its use in healthy human sins. The effect of vaccine stimulation of the human immune response was observed by observing the levels of T cells and neutralizing antibodies.
“Trials have shown that the single-dose new adenovirus type 5 vector COVID-19 (Ad5-nCoV) vaccine can produce virus-specific antibodies and T-cells within 14 days, making it a potential candidate for further research,” said Wei Chen of the Beijing Institute of Biotechnology. “
The data in the report are encouraging, but there are some warning signs. In the trial, the researchers tested three dose levels, in which most subjects experienced some degree of mild to moderate side effects, including fever, headache and fatigue.
The biggest problem Ad5-nCoV may face in a broader Phase II clinical trial is the inconsistency in its ability to produce effective antibodies and T-cell immune response. The vaccine uses a common cold virus called adenovirus 5 (Ad5) to pass genetic material and ultimately train the immune system to fight the SARS-CoV-2 virus. The problem found in these early data was that subjects with higher pre-immune levels of Ad5 appeared to have significantly reduced their response to the vaccine’s antibodies and T-cells.
“Our study found that pre-existing Ad5 immunity can slow the rapid immune response to SARS-CoV-2 and also reduce the peak level of the response,” said Feng-Cai Zhu, deputy director of the Centers for Disease Control and Prevention in Jiangsu Province, China. In addition, pre-existing high Ad5 immunity may also have a negative impact on the persistence of the vaccine-induced immune response. “
This inconsistency in the immune system response may indicate that the Ad5-nCoV vaccine may not be effective in older subjects because they may have higher levels of pre-immune levels for this common adenovirus. In response, Michael Mina, from the Harvard School of Public Health, told STATNews that this is a common problem with vaccines using the adenovirus delivery system.
Another vaccine that has progressed to more advanced clinical trials is ChAdOx1 nCoV-19, developed by scientists at the University of Oxford. In the first phase of the trial, scientists injected more than 1,000 subjects with drugs, and they will then recruit more than 10,000 subjects, covering a larger age level that would allow for an assessment of the safety and immune response of a wider population.
Although the University of Oxford has not officially published human trial data on the vaccine, a recently published preprint study outlines the successful results of preliminary animal studies. The Oxford vaccine also uses a common cold virus as its primary delivery system, which is a different adenovirus than the Ad5-nCoV vaccine being developed in China.
In the next phase of testing, Oxford will rely on new coronary pneumonia to continue to spread at a high enough rate in the local community to determine the efficacy. Scientists don’t plan to deliberately test vaccines with volunteers infected with the virus, so they need relatively high rates of viral transmission in the community to evaluate success.
Adrian Hill, of the Oxford Vaccine Group, said researchers now face a ironic taste – a decline in community transmission levels could significantly slow progress in vaccine testing. “It’s a race against viruses and time. Earlier this year, we said there was an 80 per cent chance that an effective vaccine would be developed by September. But now, we have 50% of the likely results and nothing. We are in a very strange situation and we hope that the new corona virus will stay, at least for a while. “
The two new coronary pneumonia vaccines, as well as moderna’s vaccines, may be the best-in-class vaccines currently under development, but in fact seven more vaccines are in the early stages of human trials, and more than 100 more are in preclinical development.