Researchers have encouraging news about the possibility of COVID-19 immunity. They examined patients who suffered SARS infections in 2003 and found that some still had protective T cells in their bloodstream.

According to the Daily Mail, this could mean that people who are infected with the coronavirus, which is similar to the SARS virus, may also develop some immunity against reinfection. Studies have shown that people can lose antibodies in months.

Researchers at King's College London analyzed the blood of infected patients and healthcare workers and found that the levels of protective antibodies peaked about three weeks after the first symptoms appeared. However, those antibodies were found in only 17% of the patients three months later.

On the other hand, T cells may offer long-term protection against the virus, say experts, even if the antibodies do not.

According to the study led by the Duke-NUS Medical School in Singapore, 23 SARS patients submitted blood samples that were examined for any immune cells still effective against the virus. They all had T cells, which suggests they could fight off future infections.

The researchers wrote that their findings "support the notion that COVID-19 patients will develop long-term T Cell immunity." T cells are a type of white blood cell that helps the immune system fight off disease.

Even more surprisingly, the researchers then applied the T cells to SARS-Cov-2 viruses, the pathogens that cause COVID-19, and found "robust" reactivity against SARS-2 as the cells latched onto them. The scientists also discovered SARS-CoV-2-specific T cells in people who had not been exposed to either virus, and speculated that our immune systems may have developed some kind of immunity from exposure to other viruses, such as the common cold.

Scientists at the La Jolla Institute for Immunology in California also found T cells that recognized and responded to SARS-CoV-2 in blood samples collected between 2015 and 2018. They published their findings in the journal Cell.