Using Trimer-Tag technology, Clover began developing the vaccine candidate in late January 2020. The trimer subunit resembles the native trimeric viral spike protein of SARS-CoV-2, which is responsible for binding to host cell surface ACE2 and subsequent viral entry. The trimer is produced via a rapid mammalian cell culture-based expression system developed by Clover.

Dynavax's CpG 1018 is an adjuvant used in Heplisav-B, a hepatitis B vaccine approved by the U.S. Food and Drug Administration. The technology is well-established and has been proven safe, potentially enabling accelerated development and large-scale manufacturing of a COVID-19 vaccine, according to the company.