Q19. Should we install the crosswind air barrier for vaccinated residents?

Yes, it is very good idea to install the crosswind device.  Although the best COVID-19 vaccines have an efficacy of around 95%, elderly are far more frail to risk being in that 5% who can contract this disease.  If your building has 100 residents, 5 of those can become infected if there is an asymptomatic young employee who is spreading the virus even though he may be vaccinated himself.  So adding the crosswind solution will reduce those random residents at 5% risk to near-zero, a welcome reduction for such a low-cost and easy-to-implement solution. Keep in mind that there are other benefits, like seasonal flu reduction (see Question Q4) and very clean healthy air not just for residents, but for your employees as well, at very low maintenance cost.