My opinion. Natural immunity is best option. Vitamins C, D3, zinc, quercetin, selenium, lysine, garlic, probiotic & liquid structured silver build immune. Daily exercise. Fresh air & sunshine. Healthy diet. No drugs, alcohol, smoking or vaping. No fast food or junk food. Thats my personal program. That's in my opinion the way to go to build your immune system! But my way doesn't make Big Pharma rich. My way saves America, which makes Joe Biden unhappy- because he is owned by China.