Scientists have found out why the risk of contracting COVID-19 again is extremely low
Antibodies have become commonplace in this pandemic era, suggesting that they are the best way to tame the deadly coronavirus. But when important data on COVID-19 vaccines were released the other day, the spotlight was on an unsung immune player: T cells. Tells about it Bloomberg.
AstraZeneca Plc, Pfizer Inc. and BioNTech SE, as well as China's CanSino Biologics Inc. welcomed the presence of these cells in vaccine recipients as a sign that their experimental trials are working.
T cells, or T lymphocytes, remind us that the body's defenses rely on more than one weapon, and that much of the immune response to COVID-19 is still a mystery - especially after researchers found that the vaunted antibodies lack endurance.
“Antibodies are just a small part of the picture,” said Paul Griffin, assistant professor of medicine at the University of Queensland in Brisbane, who is conducting clinical trials in Australia for two potential COVID-19 vaccines. “But we really have not yet reached the goal of fully understanding human immunity to the new coronavirus.”
At first, scientists focused on antibodies (proteins that adhere to and block foreign organisms), because their detection is the basis for most successful vaccines. Immune proteins are also easier to measure than T cells and can be used to assess past infection.
Research showing that antibodies are rapidly decreasing in patients with mild disease has dashed hopes that antibodies would provide some lasting form of immunity.
T cells, on the other hand, are capable of killing virus-infected cells, “remembering” past illnesses for decades, and awakening new antibodies to fight viruses long after the first antibodies have left the “battlefield”. For example, people infected with the coronavirus that caused the SARS epidemic in 2003 still have a T-cell response to the disease - 17 years later.
This suggests that T cells, at least hypothetically, may be ready to protect survivors from SARS almost two decades later - both from the same infection and to strengthen their protection from COVID-19, Griffin noted.
“They may have a slightly milder form or a shorter duration of the disease, but I certainly don't think that will protect completely,” he said.
One study found that some asymptomatic patients with COVID-19 had T cells that recognized the virus - even when no antibodies were found. Another pointed to a certain level of immunity in people who had never encountered the current strain of coronavirus: perhaps due to exposure to one or more long-known coronaviruses that cause the common cold.
More research is needed to determine if the T-cell response to the virus can explain why some COVID-19 patients experience little to no symptoms, while others get very sick and even die. It is clear that a balance of both antibodies and T cells is required for optimal protection, Griffin says.
Corey Smith, head of immunology at the QIMR Berghofer Medical Research Institute in Brisbane, says the findings about the short lifespan of antibodies do not mean that immunity completely disappears, precisely because of the presence of T cells.
So-called helper T cells and memory T and B cells are able to induce the primary production of antibodies to respond to an infection before it causes severe symptoms, said Smith, who is studying the immune response to the SARS-CoV-2 virus.
The current virus, like other common cold-causing coronaviruses, can evade antibodies, Smith said, leading to reinfection.
“But cellular immunity is enough to suppress any serious symptoms,” the expert says.
Perhaps it is T cells that ultimately suppress and dull the pandemic virus that killed more than 600 people in less than seven months.
“If we can't eradicate it, will it become something like a circulating virus, another common cold virus? Says Smith. "I'm not sure, but it's interesting."
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