The viral protein known as ORF3b limits the induction of the type I interferon response, which typically alerts other immune system components to the presence of a virus, in cultured cells.

The coronavirus known as SARS-CoV-2, the causative agent of the COVID-19 pandemic, induces a puny innate immune response compared other respiratory viruses such as the flu. In a preprint posted on bioRxiv on May 12, researchers have shown in cell culture that a viral protein called open reading frame 3b (ORF3b) actively blocks the induction of type I interferon, a crucial aspect of that response.