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Researchers investigating what may determine whether a novel coronavirus vaccine candidate proves successful say they have found evidence that suggests previous exposure to a coronavirus, like one that causes the common cold, could possibly provide some form of protective immunity against COVID-19.

The team, at La Jolla Institute of Immunology, studied a group of 20 adults who had successfully recovered from COVID-19 and found that the body’s immune system is able to recognize SARS-CoV-2 “in many ways,” according to their research, which was published in the journal Cell.

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“If we had seen only marginal immune responses, we would have been concerned,” Dr. Alessandro Sette, one of the lead authors, said in a news release. “But what we see is a very robust T cell response against the spike protein, which is the target of most ongoing COVID-19 efforts, as well as other vital proteins. These findings are really good news for vaccine development.”

The team tested whether the T cells isolated in patients who had recovered without suffering major complications were able to recognize protein fragments from the virus. They found that almost all patients had developed a T cell response that helps antibody production.

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“We specifically chose to study people who had a normal disease course and didn’t require hospitalization to provide a solid benchmark for what a normal immune response looks like since the virus can do some very unusual things in people,” Sette said, in the news release.

Sette said the results provide researchers with a base to compare immune system responses in people who have severe outcomes versus those who are asymptomatic or can recover at home. It also, Sette said, provides them with a baseline for determining whether the immune response in people who receive a vaccine resembles what you would see in a protective immune system response to COVID-19.

What’s more, they wrote, is that they looked at T cell response in blood samples that were collected between 2015 and 2018, which is before SARS-CoV-2 was discovered, and saw that many also contained significant reactivity against the virus despite not having previous exposure. The researchers say this may be caused by exposure to one of the other coronaviruses, like those that cause the common cold.

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“Given the severity of the ongoing COVID-19 pandemic, any degree of cross-reactive coronavirus immunity could have a very substantial impact on the overall course of the pandemic and is a key detail to consider for epidemiologists as they try to scope out how severely COVID-19 will affect communities in the coming months,” Dr. Shane Crotty, another study author, said in the news release.

The authors acknowledged that a lack of detailed information regarding common cold history or matched blood samples pre-exposure to SARS-CoV-2 “prevents conclusions regarding the abundance of cross-reactive coronavirus T cells before exposure to SARS-CoV-2 and any potential protective efficacy of such cells.”