For the virus to invade human airway cells, it has to attach via its spike protein to the ACE-2 receptor on the surface of those airway cells.

Some medications seek to dampen the catalytic activity of ACE-2 by binding to the ACE-2 active site. However the body’s reaction to those drugs is to produce more ACE-2 receptors, though the drug will still work providing it is in ‘excess’ over the ACE-2 molecules.

But the drug, blocking the catalytic site, does not necessarily block the binding site of the virus protein. Hence the result of the drugs may be to increase the number of available receptors for the virus gain access to the cells.

Thus those with diabetes or hypertension may not be at higher risk because of their condition; but because of their meds.

The drugs involved are ACE inhibitors and angiotensin II type-I receptor blockers (ARBs) used to treat diabetes and hypertension, plus thiazolidinediones and ibuprofen.

Are patients with hypertension and diabetes mellitus at increased risk for COVID-19 infection? (Lancet article)