Claims about thymosin boosting the immune system for COVID-19 lack scientific validation due to the absence of placebo-controlled clinical trials.

“A: I’m seeing a lot of claims out there trying to increase sales. Unless there’s a placebo-controls clinical trial you can find in a scientific journal (e.g. PubMed), you can’t be sure any claims are true. The small protein called thymosin comes originally from a thymus fraction and is thought to help with thymus function. Given that the thymus shrinks with age, it is hypothetically possible thymosin might help recover from COVID-19 ... but I haven’t seen any clinical trials showing this so at best it’s speculation. If anyone has clinical data on thymosin in COVID-19 patients, it would be great to know.”