COVID-19 vaccines stabilize the spike protein in a pre-fusion conformation using proline amino acid insertions.

“And the reason that's really important is because all of the vaccines that are available in the United States under either emergency use authorization or under FDA authorization or up and coming vaccines, so that includes the Moderna and the Pfizer-BioNTech mRNA vaccines, the Johnson & Johnson adenoviral vaccine, as well as the Novavax vaccine, they all contain an insertion of two proline amino acids into the spike protein to lock it into the pre-fusion conformation.”