An Oxford University group and the British-Swedish pharmaceutical company AstraZeneca, which together are developing a leading vaccine candidate against the novel coronavirus, reported in a medical journal on Monday that their Phase 1 human trial showed their vaccine to be safe and that it stimulates the body to produce both antibodies and white blood cells to fight off infection.
The study of 1,077 volunteers was described as very promising. The report in the British medical journal The Lancet suggested that so far the vaccine appeared safe and was able to conjure a promising immune response.
At this early stage, the vaccine has not proven itself to protect people from infection or illness.
But with hopes soaring that vaccines will soon emerge to quiet the global pandemic, Britain and the United States have already ordered millions of doses of the Oxford vaccine.
The Oxford vaccine is named ChAdOx1 nCoV-19 and was made from a weakened and non-replicating version of a common cold virus, an adenovirus. The vaccine has been engineered to express a bit of the coronavirus that produces the spike protein the virus uses to enter and infect human cells.
An editorial in The Lancet warned, “The race for a vaccine moves fast, as the need for a solution is evident, but we cannot forget that safety is of the highest importance.”
Infectious-disease experts caution that vaccines must be widely administered to protect the general population, and in an era of widespread skepticism, and even overt hostility toward science, any vaccine that greatly underperforms or causes serious side effects will set back the entire effort.
The Oxford vaccine candidate is one of a handful that the United States plans to test later this summer in large clinical trials with about 30,000 people, half of whom receive the vaccine and half who do not.
The U.S. government has invested $1.2 billion in that vaccine candidate, and secured 300 million doses.
The Oxford candidate is one of 23 vaccines now being tested in human trials, according to a running tally kept by the World Health Organization. More than 130 others are in preclinical trials.
Several vaccine candidates have stimulated an encouraging immune response in early human tests, but scientists caution that no one yet knows what level of immune response will be protective against the virus in the real world through a cross section of humanity—young to old, healthy to those with preexisting conditions.
The ultimate proof of whether any vaccine works will be large-scale clinical trials that use a flip of the coin to randomly decide whether thousands of people receive the experimental vaccine or a placebo shot—and then wait to see if the vaccinated group is protected against infection or severe disease.
The immune system uses a multipronged approach to defeat any pathogen, and it’s not yet known exactly what protects against a coronavirus infection.
Much public attention has focused on antibodies that block and neutralize the virus. Other experimental coronavirus vaccines from biotechnology company Moderna and pharma giant Pfizer have been shown to trigger antibodies at similar or greater levels than people who are naturally recovering from coronavirus infections, a benchmark that many scientists consider a hopeful sign.
But there are other forms of immune memory, including T cells, that are an area of increasing interest as evidence accumulates that antibody levels can drop off quickly in people naturally recovering from an infection.
One type of T cell, helper T cells are what Angela Rasmussen, a virologist at Columbia University, compares to “the football coach, where the coach calls the play. They’re coordinating the immune response of all the other cells in the immune system—those are really important.” The helper T cells can instruct the immune system to produce virus-fighting antibodies.
There are also “killer,” or cytotoxic T cells, which are capable of destroying infected cells.
“It is unclear the role that cytotoxic T cells play in amelioration of COVID-19 disease,” Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia said in an email. “It is, in a sense, a second line of defense.”