MONDAY, July 20, 2020 (HealthDay News) -- The highly anticipated results of two early-phase clinical trials of candidate COVID-19 vaccines suggest they are safe and may protect recipients, although the duration of the effect is still unknown.
"We are rapidly moving to an era in which a vaccine against the novel coronavirus is becoming a reality," noted Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security in Baltimore.
Adalja wasn't involved in the new trials, but called them "encouraging and important, as they represent phase 1 and 2 data on larger groups of patients."
The largest and longest of the two trials was conducted among 1,077 adult Britons averaging 35 years of age, none of whom had any prior known exposure to SARS-CoV-2, the new coronavirus.
As reported July 20 in The Lancet, a team led by Andrew Pollard at the University of Oxford said the vaccine effectively stimulated two arms of the immune system against the virus.
"The immune system has two ways of finding and attacking pathogens -- antibody and T cell responses," Pollard explained in a journal news release. "This vaccine is intended to induce both, so it can attack the virus when it's circulating in the body, as well as attacking infected cells."
People in this phase 1/2 trial received either the experimental vaccine or a "control group" vaccine (in this case, the meningitis vaccine), delivered in U.K. hospitals between April 23 and May 21. The data released Thursday includes results from the first eight weeks of the trial.
According to Pollard's group, blood samples taken from recipients found strong immune system antibody responses, as well as strong T-cell responses in those who got the coronavirus vaccine.
That's crucial, because activating both of these responses -- which recognize, target and destroy cells infected with SARS-CoV-2 -- is key to a successful vaccine, the researchers said.
Any ideal vaccine would confer such a protective effect for at least six months, but of course the trial is currently only at week eight. Still, T-cell responses appeared to peak 14 days after vaccination, the researchers said, and had only dipped slightly by day 56.
Antibody responses peaked by day 28 and were still high by day 56, the group added.
Giving people a second "booster" shot of the vaccine appeared to boost the antibody response but didn't have an effect on the T-cell response.
As to side effects, Pollard's team said there were no serious effects in the hundreds of people vaccinated, although transient mild/moderate effects were common -- symptoms such as fatigue or fever, often relieved by the use of a painkiller (such as acetaminophen) were common.
Despite all this early promise, study co-author Sarah Gilbert, also of the University of Oxford, stressed that the trial is still too short to say anything about longer-term effectiveness. The study population also needs to be widened in scope, to include older people and people with underlying health conditions.
"There is still much work to be done before we can confirm if our vaccine will help manage the COVID-19 pandemic, but these early results hold promise," Gilbert said. "As well as continuing to test our vaccine in phase 3 trials, we need to learn more about the virus -- for example, we still do not know how strong an immune response we need to provoke to effectively protect against SARS-CoV-2 infection."
To create the Oxford vaccine, the researchers used a weak, genetically tweaked version of an adenovirus (the kind of virus behind the common cold) that typically infects chimpanzees. The genetic tweaking involved modifying the adenovirus so that it contained a "spike protein" structure on its surface that mimicked one found on SARS-CoV-2.
"This means that when the adenovirus enters vaccinated people's cells it also delivers the spike protein genetic code," Pollard explained. "This causes these people's cells to produce the spike protein, and helps teach the immune system to recognize the SARS-CoV-2 virus."
A similar approach was used by Chinese researchers to help produce a second candidate vaccine, with trial results also reported in The Lancet.
In the phase 2 trial, a team led by Feng-Cai Zhu of the Jiangsu Provincial Center for Disease Control and Prevention, had 382 people receive either a high or low dose of the candidate vaccine, while another 126 got a "dummy" placebo shot.
Two-thirds of participants were between 18 and 44 years of age, one-quarter were between 45 and 54, and the remaining 13% were aged 55 or older.
By 28 days after vaccination, 95% of people who got the high-dose shot, and 91% of those who got the lower dose had either a T cell or antibody immune system response, Zhu's group said.
"Adverse reactions" to the vaccine -- symptoms such as fever, fatigue or injection-site discomfort -- were common, with about three-quarters of recipients reporting such symptoms. But the researchers classified most of these reactions as mild or moderate.
As with the British trial, questions remain as to the duration of protection, and because no participants were intentionally exposed to SARS-CoV-2 as part of the trial, it's still unknown how effective the shot might be in real-world conditions.
More research lies ahead, both teams said. For their part, the Oxford team noted that a U.K.-based phase 2 trial is already underway, and even more advanced phase 3 trials (conducted in the United Kingdom, Brazil and South Africa) are also happening.
An effective vaccine that lasts over the long term is the world's best hope for an early end to the COVID-19 pandemic. Over 250 candidate vaccines are currently under investigation worldwide, with billions of dollars poured into this research.
The U.S. Centers for Disease Control and Prevention has more on the new coronavirus.
SOURCES: The Lancet, news release, July 20, 2020; Amesh Adalja, MD, infectious disease specialist and senior scholar, Johns Hopkins Center for Health Security, Baltimore