It turned out that for those people, exposure to other human coronaviruses, such as those that cause cold-like symptoms, had helped their bodies to fight off the novel coronavirus. This is because T-cells, a critical part of the body’s immune response, were able to recognize and target genetic elements of prior seasonal coronaviruses that also happened to be present in SARS-CoV-2. That meant their bodies were able to attack the novel virus without the production of new antibodies specific to it.
Notably, the T-cells that those health care workers produced targeted a different part of the virus than the T-cells did in people who have a detectable Covid infection. Swadling said the while the T-cells produced by both vaccines and a detectable Covid-19 infection attack the frequently mutating spike protein of a virus, these health care workers’ T-cells instead targeted the virus’ internal machinery. Researchers call these T-cells that appear effective against different coronaviruses “cross-reactive.”
“We identified new parts of the virus that we can put into a vaccine to try to improve it ,” Swadling said. These improvements, he said, could make vaccines better at preventing infection, more effective against new variants and more protective for immunocompromised individuals.
Immunity to a virus occurs when the body is able to recognize a pathogen and effectively fend off infection or disease. Antibodies, such as those acquired from a vaccine or previous infection, attack a virus as soon as it enters the body. T-cells act as another line of defense, working to stop the spread of infection and development of disease once the virus has made it into the body. The mRNA vaccines such as those made by Pfizer and Moderna work by training the body to safely produce antibodies without infection, but they also spur the production of T-cells and B-cells. That’s why the vaccines effectively prevent hospitalization even when they don’t prevent infection altogether — even when antibodies have waned, T-cells are still there to help fight off an infection more quickly.
The study’s authors proposed that T-cells they found— the ones that target the virus’ internal machinery— may offer better protection against emerging variants because of their ability to attack a key part of the virus less vulnerable to mutations than its spike protein. They theorize that targeting those areas of the virus could make the shots more effective.
As labs work to develop a single shot that would offer broader protection against any Covid variant, at least one company, Gritstone Bio Inc., is looking to put Swadling’s theories to the test. Others have reached similar conclusions as Swadling and his colleagues. One study found that in households where some people remained Covid-free despite exposure, those people also appeared protected by T-cells from past exposure to coronaviruses. Another study from January found that some children who did not develop Covid antibodies also had cross-reactive T-cells, which may be part of the reason why children generally have milder symptoms.
Knowing how many people have this heightened immune response is extremely difficult to assess. Some people may have managed to avoid the virus through continued caution or simply luck. But perhaps more important than knowing how many people fall into this category is the information about immunity that can be gathered from studying what sets them apart.
“T-cells are very long-lived so we may not need repeated vaccination,” Swadling said.
Studying the super-immune, he said, may help us against omicron — and any future variants of concern.
This article was provided by Bloomberg News.