  We present a new photometric calibration of the WFC3-UVIS and WFC3-IR
detectors based on observations collected from 2009 to 2020 for four white
dwarfs, namely GRW+70~5824, GD~153, GD~71, G191B2B, and a G-type star, P330E.
These calibrations include recent updates to the Hubble Space Telescope primary
standard white dwarf models and a new reference flux for Vega. Time-dependent
inverse sensitivities for the two WFC3-UVIS chips, UVIS1 and UVIS2, were
calculated for all 42 full-frame filters, after accounting for temporal changes
in the observed count rates with respect to a reference epoch in 2009. We also
derived new encircled energy values for a few filters and improved sensitivity
ratios for the two WFC3-UVIS chips by correcting for sensitivity changes with
time. Updated inverse sensitivity values for the 20 WFC3-UVIS quad filters and
for the 15 WF3-IR filters were derived by using the new models for the primary
standards and the new Vega reference flux and, in the case of the IR detector,
new flat fields. However, these values do not account for any sensitivity
changes with time. The new calibration provides a photometric internal
precision better than 0.5% for the wide-, medium-, and narrow-band WFC3-UVIS
filters, 5% for the quad filters, and 1% for the WFC3-IR filters. As of October
15, 2020, an updated set of photometric keywords are populated in the WFC3
image headers.
