Medical research teams in England and China are reporting that COVID-19 vaccines being developed are prompting a protective immune response against the coronavirus in subjects that have been injected with the new formulations. This is good news, as other researchers have found that the antibodies produced from a direct infection by the SARS-CoV-2 coronavirus are comparatively short-lived, and may not be reliable in preventing future infections.
Amongst the more than 160 COVID-19 vaccines currently in development, research teams at Oxford University’s Jenner Institute and China’s CanSino Biologics have announced that test subjects that are part of their respective vaccine candidate’s clinical trials are showing promising immune responses to the test drugs.
“We are seeing [a] good immune response in almost everybody,” explains Dr. Adrian Hill, director of the Jenner Institute at Oxford University. “What this vaccine does particularly well is trigger both arms of the immune system.”
The two “arms” Hill is referring to are the production of antibodies that can neutralize the SARS-CoV-2 virus, and a response from the immune system’s T-cells, specialized “hunter/killer” cells that either directly or indirectly eliminate harmful pathogens.
A larger clinical trial in the U.K. involving 10,000 subjects is still underway, and another one in the U.S. with 30,000 subjects is scheduled to start soon. This first trial tested two treatments of the vaccine on each subject, each administered four weeks apart, with the second shot possibly adding to the robustness of the immune system’s response. The two-pronged approach from within the immune system is also expected to provide extra protection. “There’s increasing evidence that having a T-cell response as well as antibodies could be very important in controlling COVID-19,” according to Hill.
The Oxford vaccine is made using a deactivated cold virus harvested from chimpanzees that has been altered to carry the spike proteins that enables the SARS-CoV-2 virus to latch on to human cells. This combination allows the inactive virus particles to attach themselves to human cells’ ACE-2 receptors, prompting a comparative immune response, but without viable genetic material the virus can’t actually infect the host cell.
The CanSino Biologics vaccine candidate is similar to the one produced by the Oxford team, although it uses an inactive human cold virus as its base, a factor that may have caused a less active response in the bodies of subjects that recognized the virus. Regardless, the vaccine has been approved by China’s government for use by the military while final-stage trials continue.
Oxford reports that their vaccine (called ChAdOx1 nCoV-19) is so far only producing minor side effects, such as fever, chills and muscle pain, although these symptoms are occurring more often than in subjects in the study’s control group who received a meningitis vaccine.
Antibodies are Y-shaped protein molecules produced by the immune system that are keyed to either mark a specific bacterium or virus for attack by the immune system, or used to overwhelm the pathogen directly by smothering it in antibodies. Unfortunately, numerous studies have found that naturally-acquired antibodies fade from the body rather quickly, meaning that patients that have recovered from COVID-19 probably won’t be able to rely on a natural immunity against future infections.
One study found that 65 days after being infected only 17 percent of symptomatic patients still had a useful amount of COVID-19 antibodies in their bloodstream. Patients that didn’t develop symptoms tended to produce fewer antibodies to begin with, resulting in even lower levels of the valuable molecules.
“More and more studies actually show that individuals, especially with mild disease, tend to lose these antibodies over time,” according to Kamran Kadkhoda, PhD, medical director of the immunopathology lab at Cleveland Clinic. “Whether that means they’re at risk of reinfection? That remains a possibility.”