This worked for me, but not sure if it works in every case.
At first, some vitamins that include a high daily dose of vitamin C (1000 mg). There are some combinations especially crafted for increasing immunity. All-purpose vitamin and mineral supplements don't really work if you have strong deficits in certain areas. Later, I switched to a supplement based on (mainly) bee-hive products (including royal jelly, propolis, etc.) Since we are on Hive, that seems appropriate, lol. Of course, it matters what you eat, but although I eat plenty of fruits and vegetables, looks like I don't absorb enough vitamins. This may not be the case for everyone. Others may have better absorption.