The antibodies elicited by the "S2 vaccine" not only neutralize COVID's multiple strains but also coronaviruses that cause the common cold.

All currently licensed COVID vaccines target the spike protein’s S1 region, which is prone to mutations and is highly variable across different coronaviruses.
Another region of the spike protein, S2, mutates very little and is similar in all variants of SARS-CoV-2 as well as coronavirus strains that cause the common cold.
Mice vaccinated against S2 created antibodies that neutralized multiple animal and human coronaviruses, including common cold coronaviruses; the original strain of SARS-CoV-2; the D614G mutation that dominated in the first wave; the Alpha, Beta, Delta, and original Omicron strains; and two bat coronaviruses.