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A new study reveals why you may not get the coronavirus despite being in close contact with someone who has it.
Nature.com reports researchers assessed 52 COVID-19 household contacts in order to observe the individuals' immune responses at the earliest timepoints following exposure to SARS-CoV-2.
The study found that individuals who were previously exposed to other coronaviruses were able to make memory immune 'T cells' which provided protection against SARS-CoV-2.
Researchers found that the memory T cells created were responsible for some household contacts testing negative despite being in close proximity to someone who had tested positive.
Additionally, despite varying coronaviruses causing different illnesses and behaving in different ways, they still share similar characteristics within the COVID family and structural similarities allow immune cells to recognize the COVID types from each other.
Researchers tested blood from immune cells beginning on the first day and again on the sixth day of trials to find higher levels of memory T cells in samples who tested negative on a PCR test than individuals who tested positive.
The authors of the study concluded that levels and speeds at which the cells became active after being exposed to a positive case within their household suggest the cells existed from previous infections and weren't created immediately after the latest exposure to COVID-19, which is why the individuals in close contact didn't test positive themselves.
The pre-existing T cells are believed to have triggered an immune response that quickly combatted the SAR-CoV-2 virus prior to the person becoming infected and it leading to a positive PCR test result, while T cell levels for those who tested positive weren't as high.
You can read results from the full study here.