Reinfection occurs when our nitric oxide levels are low. I learnt this the hard way because I kept getting reinfected.

L-Arginine(amino acid) increases nitric oxide and nitric oxide balances the autonomic nervous system so the body can heal. L-Arginine (HCL) powder actually works. Start low at 1-1.5grams per day and increase after a couple weeks. A Vitamin K2 supplement is also helpful if you aren't getting it from food.

Long Covid fatigue caused by an Arginine deficiency : covidlonghaulers (reddit.com)

l-Arginine Augments Cardiac Vagal Control in Healthy Human Subjects | Hypertension (ahajournals.org)