Are clean outs required at bathroom vanity drains ?

The IRC read as follows;

P3005.2.4 Change of direction. Cleanouts shall be installed at each fitting with a change of direction more than 45 degrees (0.79 rad) in the building sewer, building drain and horizontal waste or soil lines. Where more than one change of direction occurs in a run of piping, only one cleanout shall be required in each 40 feet (12 192 mm) of developed length of the drainage piping.

and;

P3005.2.6 Base of stacks. A cleanout shall be provided at the base of each waste or soil stack.

also;

P3005.2.9 Cleanout size. Cleanouts shall be the same nominal size as the pipe they serve up to 4 inches (102 mm). For
pipes larger than 4 inches (102 mm) nominal size, the minimum size of the cleanout shall be 4 inches (102 mm).

Exceptions:
1. “P” trap connections with slip joints or ground joint connections, or stack cleanouts that are not more than one pipe diameter smaller than the drain served, shall be permitted.

and;

P3005.2.10 Cleanout equivalent. A fixture trap or a fixture with integral trap, readily removable without disturbing concealed piping shall be acceptable as a cleanout equivalent.

So it all depends on the layout of your system. The only time you need a cleanout at a fixture is if it's needed to rod out the line and the P trap is non-removable.

Evenwhen they are not "required" I would install them.

In Massachusetts we are required to have a clean out on the kitchen sink drain and is good to have them on back to back installations because we cant use double wyes or double fixture fittings.