"Micronutrient deficiencies can have devastating consequences."
https://www.cdc.gov/nutrition/micronutrient-malnutrition/micronutrients/index.html
"Such micronutrient deficiencies may limit the effectiveness of the COVID vaccines.
We propose that a nutritional supplement (e.g. containing vitamins A, B6, B9, B12, C, D and E and the minerals Zn, Cu, Se and Fe) should be provided free of charge to all those aged over 70 years for a period of weeks before and after they receive the vaccine. The additional cost of providing a supplement of those nutrients important to immune function that are likely to be insufficient or deficient in the elderly would be a small investment to better assure a robust vaccine response."
https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/optimising-covid19-vaccine-efficacy-by-ensuring-nutritional-adequacy/5F25F117DED5141638554BAAFC66E1FF
"A deficiency of micronutrients results in impaired immune responses leading to improper secretion of cytokines, alterations in secretory antibody response and antibody affinity which increases susceptibility to viral infection. The deficiency of various micronutrients in COVID-19 patient can be treated by appropriate nutritional supplements, prescribed after evaluating the patients' nutritional status."
https://pubmed.ncbi.nlm.nih.gov/33544528/
"Physicians worldwide are largely interested in vitamin and mineral supplements to help them battle COVID-19 whether through protection or treatment. Dietary supplementations especially vitamin D, vitamin C, and Zinc offer good prophylactic and therapeutic support to the currently available treatment regimens. They are relatively safe and were proven to aid recovery in other respiratory infections."
https://pubmed.ncbi.nlm.nih.gov/35656948/
"A higher risk for severe clinical courses of coronavirus disease 2019 (COVID-19) has been linked to deficiencies of several micronutrients."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9101904/
Endogenous Deficiency of Glutathione as the Most Likely Cause of Serious Manifestations and Death in COVID-19 Patients
https://pubmed.ncbi.nlm.nih.gov/32463221/
"There are many reasons why a blood test for minerals and vitamin deficiencies may be recommended."
https://www.healthcheckup.com/general/blood-test-for-minerals-and-vitamin-deficiencies/