Health care workers, that's about it.
Anyone who wants to travel internationally will have to show proof of immunity via vaccination. That much is a certainty, also nearly every private insurance company who sponsors private health-care for incorporations will almost certainly require their policy holders to require it as a precondition of employment and also in right to work states a condition of continuing employment. There will be no avoiding it. Domestically access to stadiums, mass transit, aircraft could and most likely will require proof for unrestricted access. London Heathrow Airport is already testing digital immunity passports with other EU member states it will be the norm.