"We have worked so hard as a country to fight the pandemic," Hancock said in the letter. "The last thing I would want is for my private life to distract attention from the single-minded focus that is leading us out of this crisis."
Britain's successful vaccination campaign contrasts with Europe, which has struggled with its own rollout and has been seeing a fresh surge in infections.
He said Britain had entered into a partnership with the manufacturer CureVac to develop vaccines that could be quickly adapted as new strains were identified.
Health Secretary Matt Hancock said the Midlands, the north east, parts of the north west and parts of the south west would be moved into Tier 4 from 00.01 on Thursday.
Unfortunately this new variant is now spreading across most of England and cases are doubling fast.
The number of new deaths recorded within 28 days of a positive COVID test also rose to 414 from Monday's 357, taking the total since the start of the pandemic to 71,567.
He said he felt "quite emotional" seeing the pictures of the first vaccination taking place, adding that the programme was starting across 70 hospitals in the UK.