Preliminary results from the UK's Oxford Covid-19 vaccine trial and a trial conducted in China show that both vaccines are generally safe and produce an immune response. Both studies are reported in The Lancet, and though it is too early to tell if the approaches meet the requirements to be an effective vaccine against Covid-19, it's a promising sign, and further investigations are already underway.
Both vaccines use a weakened adenovirus, the common cold virus, which was genetically modified to carry the genetic code of the spike proteins on the outer shell of SARS-CoV-2, the virus responsible for Covid-19.
For the Oxford Study, the cold virus came from chimps and was administered to 543 of the 1,077 healthy adults who took part, while the remaining 534 made up a control group and were given a meningitis vaccine. The results so far have found that the Covid vaccine induced strong antibody and T cell immune responses up to day 56 of the ongoing trial.
“The immune system has two ways of finding and attacking pathogens – antibody and T cell responses,” team leader Professor Andrew Pollard of the University of Oxford, said in an emailed statement. “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. We hope this means the immune system will remember the virus, so that our vaccine will protect people for an extended period. However, we need more research before we can confirm the vaccine effectively protects against SARS-CoV-2 infection, and for how long any protection lasts.”
The vaccine has shown to be able to provoke a T cell response within 14 days, which means the immune system can find and dispose of cells infected with the virus. Within 28 days, there was also an antibody response, which means the immune system dispatched antibodies to attack the virus if found present in the blood or in the lymphatic system.
Minor side effects such as fatigue and headaches were reported by about 70 percent of the participants, but were less intense in the participants who were allowed to take paracetamol. Taking this before and after the vaccination had no negative effect on the outcome.
The Chinese study saw 508 participants taking part in a phase II trial. Of the participants, 253 received a high dose of the vaccine, 129 received a low dose, and 126 received a placebo. Ninety-five percent of the high-dose group and 91 percent of the low-dose group showed either T cell or antibody immune responses at day 28 post-vaccination. The patients were not followed further than 28 days so long-term immunity was not investigated.
The ideal vaccine ought to have minimal side effects and be effective after one or two doses. It needs to work in target populations (especially the most affected ones such as the elderly and people with pre-existing medical conditions), should provide protection for at least half a year, and reduce the spread of the virus. These two vaccines are yet to confirm that they have these capabilities, but they, and another recently published vaccine that produced antibodies against Covid-19, are the most promising candidates we have so far
“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," co-author Professor Sarah Gilbert, also from the University of Oxford, added. However, she cautioned there is still a way to go yet. "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,” she said.
"If our vaccine is effective, it is a promising option as these types of vaccine can be manufactured at large scale. A successful vaccine against SARS-CoV-2 could be used to prevent infection, disease, and death in the whole population, with high-risk populations such as hospital workers and older adults prioritised to receive vaccination.”
According to the latest figures over 14.5 million people have been infected with the disease across the world.