One takeway from the Pfizer & Moderna trials was that a single dose of those vaccines were also fairly protective for most people. With those vaccines, if you c

One takeway from the Pfizer & Moderna trials was that a single dose of those vaccines were also fairly protective for most people. With those vaccines, if you could avoid being infected within two weeks of the first dose, it looks like the protection is ~ 90% against COVID. The second dose acts as a booster, and with J&J, a second dose does indeed increase the antibody titre about three fold. That said, a single dose of any of these vaccines is probably "good enough". Couple of caveats: With Pfizer & Moderna, the major difference in outcome for single dose participants was a reduced protection from 'severe COVID', down to about 50%. It's also a very small group (~1000 people), so there's the risk of over interpreting the results. The other thing to consider is that a second dose might be required for older adults, who have a reduced immune response from a single dose.