Scientists around the world are competing to develop a coronavirus vaccine, and epidemiologists are trying to predict how the pandemic will develop until such a vaccine becomes available.

However, both efforts are surrounded by unresolved uncertainty about whether the immune system can generate a substantial and sustained response to the coronavirus, and whether exposure to circulating viruses such as the common cold provides any protective immunity.

A collaboration between the laboratories of Alessandro Sette, Dr. Biol. Sci. and Shane Crotty, Ph.D., at the La Jolla Institute of Immunology is beginning to fill the mass knowledge gap with good news for vaccine developers and is providing the first cellular immunology data to help guide recommendations for social distancing, according to Science Daily.

The report ‘Targets of T cell responses to SARS-CoV-2 coronavirus in humans with COVID-19 disease and unexposed individuals’ reveals that 38% of people tested had cell-based immunity despite not contracting the coronavirus.

The study analyzed the response of T cells in blood samples that had been collected between 2015 and 2018, before the coronavirus began circulating. Many of these individuals had significant T-cell reactivity against covid, although they had never been exposed to it. But almost all have been affected by at least three of the four coronaviruses of the common cold, which could explain the observed cross-reactivity.

However, it is not yet clear whether the observed cross-reactivity provides at least some level of pre-existing immunity to SARS-CoV-2 and therefore may explain why some people or geographic locations are more affected by the coronavirus.

“Given the severity of the current 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 for epidemiologists to consider as they attempt to determine how severely COVID-19 will affect communities in the coming months,” says Crotty, a professor at the Center for Vaccine and Infectious Disease Research.

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