1. Asymptomatic #SARSCoV2 carriers after vaccines, as aptly drawn by @nataliexdean (adapted @TheEconomist)
Even w/ the most highly effective vaccines (below), there'll likely be carriers, who can transmit, because shots aren't expected to achieve sterilization/mucosal immunity

2. The likelihood may increase over time after vaccination (with less circulating IgA levels, non-secretory) and with variants that have heightened transmissibility (like B.1.1.7).
https://www.frontiersin.org/articles/10.3389/fimmu.2020.611337/full and @VirusesImmunity https://twitter.com/VirusesImmunity/status/1284545115093172224

3. An intranasal vaccine would be ideal for that but they have taken a back seat to shots, even though they provide perfect complementarity. Single dose potential striking in experimental model https://www.cell.com/action/showPdf?pii=S0092-8674%2820%2931068-0

4. There are some early clinical trials, via @hildabast https://twitter.com/hildabast/status/1360707617966854144
but still not getting the priority they deserve here. Once validated, nasal vaccines could be quickly, widely distributed (like via mail) & accelerate our quest to reduce asymptomatic carriers/spread