The body fight it off, also identifies some parts of the novel coronavirus, according to a study whose findings might explain why some individuals have milder COVID-19 cases than others.

The research, published in the journal Science, noted that the immune system's memory T cells keep track of the viruses they've seen previously, giving the cells a headstart in recognising and fighting repeat invaders.

On the other hand, the scientists, such as those from La Jolla Institute (LJI) in the US, cautioned it is too soon to say whether such preexisting immune cell memory impacts COVID-19 clinical outcomes.

"We have proven that, in certain people, pre-existing T cell memory against ordinary cold coronaviruses may cross-recognise SARS-CoV-2, down to the specific molecular structures," said Daniela Weiskopf, a co-author of this study from LJI.

"This might help explain why some people today reveal milder symptoms of disease while some get severely sick," Weiskopf said.

Alessandro Sette, another co-author of the study from LJI, noted that the reactivity of the immune system could translate to various degrees of protection.

"Using a strong T cell response, or a much better T cell response may provide you the chance to mount a much quicker and more powerful response," Sette said.

An earlier study by Sette and his team had shown that 40 to 60 percent of people who were never exposed to the novel coronavirus SARS-CoV-2 had T cells that reacted to the virus.

According to the study, the immune system in these individuals recognised fragments of the virus it'd never seen before -- a finding that was reported among people in the Netherlands, Germany, Singapore, and the UK.

In the present research, the scientists analyzed samples collected from study participants who had never been subjected to SARS-CoV-2.

They defined the specific areas of the virus that are liable for the cross-reactive T cell response.

Their analysis showed that unexposed individuals can produce a range of memory cells that are equally reactive against SARS-CoV-2, and four types of ordinary cold coronaviruses.

Based on the finding, the scientists stated battling a cold chilly coronavirus could teach the T cell compartment to recognise several parts of SARS-CoV-2 also.

They believe this method provides evidence for the hypothesis that common cold viruses can, in fact, induce cross-reactive T cell memory from SARS-CoV-2.

"We knew there was pre-existing reactivity, and this study provides quite powerful direct molecular evidence that memory T cells can'see' sequences which are extremely similar between common cold coronaviruses and SARS-CoV-2," Sette said.

The scientists found that while many cross-reactive T cells targeted at the SARS-CoV-2's spike protein -- the region of the virus which recognises and binds to human cells -- pre-existing immune was also directed to additional SARS-CoV-2 proteins.

Sette noted that the finding is applicable because most vaccine candidates target the spike protein.

The findings, according to the researchers, suggest the hypothesis that inclusion of further SARS-CoV-2 targets might enhance the capability to make the most of the cross reactivity, and could further enhance vaccine potency.