It’s the million dollar question: Can we develop long-term immunity against SARS-CoV-2, the virus that has taken the lives of over 783,000 people worldwide as of Aug. 19.
Although there are no definitive answers, scientists believe there might be a light at the end of the immunity tunnel.
Several studies, both peer reviewed and not, have looked beyond antibodies to the rest of the highly complex immune system. Now, all eyes are on T cells and B cells — key players in the response against foreign invaders that emerge after the body has been exposed to a pathogen.
Some of these immune T cells can directly kill other infected cells being used as hosts for virus replication, while other “helper” T cells aid in the production of antibodies by helping B cells mature to get the job done.
Research released last week revealed that all 206 individuals studied who contracted COVID-19, including those with mild and severe cases, generated “robust memory T cell responses,” even in the absence of antibodies, the paper published in Cell said.
Family members who did not test positive for the coronavirus but had exposure to it also developed these special fighter cells, according to the researchers. But most surprisingly, these responses were detected months after infection, suggesting long-term immunity, but just how long remains a mystery.
That’s good news for the development of effective vaccines and knowing how close we may be to herd immunity, experts say.
“Yes, you do develop immunity to this virus, and good immunity to this virus,” Dr. Eun-Hyung Lee, an immunologist at Emory University, told The New York Times. “That’s the message we want to get out there.”
A separate study of 36 people who recovered from COVID-19 also found that all of them carried coronavirus specific T cells. What’s more, they showed that patients who recovered from severe acute respiratory syndrome — the virus behind a 2003 epidemic — 17 years ago still possessed T cells for the pathogen.
This means if exposed to SARS again, these patients could be protected from severe infection.
Although it takes the body time to produce T cells after exposure to the coronavirus, these soldiers have better memory than antibodies, which some COVID-19 patients don’t develop.
“Once the adaptive immune system has vanquished the invader, a pool of long-lived memory T and B cells are made. These memory lymphocytes remain dormant until the next time they encounter the same pathogen,” Dr. Raj Thaker, an immunology lecturer who studies T cells and B cells at the University of Essex, wrote in the Conversation.
“This time, though, they produce a much faster and stronger immune reaction. Memory is the key feature of the adaptive immune system, enabling long-term protection.”
Research on COVID-19 and antibodies, on the other hand, suggests that the fighter proteins don’t stay in the blood of recovered patients for long. One early study showed that COVID-19 antibodies remained detectable up to seven weeks after infection, but there remains no definite timeline.
Antibodies for other coronaviruses, such as those that cause the common cold, also have a short stay in the human body, experts say.
This is one of the reasons why people must get the flu vaccine every year; the other is because influenza viruses that cause the flu have a high mutation rate, making them unidentifiable to the immune system over time.
“This suggests that antibodies to COVID-19 may not last very long. But this does not exclude the existence of memory T and B cells, capable of re-emerging from their dormant states to protect against re-infection,” Thaker wrote. “In other words, the antibodies that B cells make during initial exposure disappear in a few weeks, but the memory cells generated as a consequence of this persist for much longer.”
In a twist of irony, some studies have shown that patients who were never exposed to the coronavirus had T cells in their immune system that were capable of recognizing SARS-CoV-2, McClatchy News previously reported.
These cells could have come from exposure to the common cold, which shares similar genetic information with the coronavirus, the researchers said. Scientists behind the finding say this memory of viruses past could explain why some people are only slightly affected by COVID-19, while others get severely sick.