The novel coronavirus infection (COVID-19) caused by the SARS-CoV-2 virus is now a pandemic and has culminated major morbidity and mortality globally. Studies have shown that patients with underlying type 2 diabetes mellitus (DM), obesity, old age and hypertension had a higher risk of developing severe COVID-19 infection and mortality related to COVID-19.Emerging evidence has shown that gut microbiota plays an important role in the pathogenesis of COVID-19.

HYPOTHESIS We hypothesize that modulating the gut microbiota with a microbiome immunity formula can rebalance the gut microbiota in populations at risk of infection, like, patients with type 2 DM and elderlies and can lower the number of hospitalisation and reduce side effects associated with COVID-19 vaccination.

AIM We aim to evaluate the efficacy of modulating gut microbiota with a microbiome immunity formula in vulnerable subjects (patients with underlying type 2 DM and elderlies) in improving immune functions, reducing adverse events associated with COVID-19 vaccinations and reducing hospitalisation in susceptible individuals during the COVID-19 pandemic.

STUDY DESIGN This is a double-blinded, randomized, active-placebo controlled study comparing a microbiome immunity formula and placebo in enhancing immunity and reducing hospitalisation within one year. Except two kinds of subjects (Substudy 1: Patients with Type 2 DM and Substudy 2: Elderly individual) will be included in respective substudy, all other methodologies are the same. In each substudy, at least half of the recruited subjects will plan to receive COVID-19 vaccination and start to take the study products after vaccination. Recruited subjects will be randomised to receive a microbiome immunity formula or active placebo for 3 months, with another 9 months follow-up after completion of study products.

Substudy 1

Inclusion Criteria:

1. Age 18 years - below 65 years
2. A confirmed diagnosis of type 2 DM for ≥ 3 months with stable control (i.e. no change in DM medications in recent 2 months)
3. Written informed consents obtained

Exclusion Criteria:

1. Known history of confirmed COVID-19 infection

2. Known active sepsis or active malignancy

3. Known increased infection risk due to underlying immunosuppressed state which includes:

   • Prior organ or hematopoietic stem cell transplant
   • Neutropenia with absolute neutrophil count (ANC) <500 cells/ul at the time of study inclusion
   • Known HIV infection with CD4 <200 cells/ul at the time of study inclusion
   • On concomitant immunosuppressants or corticosteroid at a dose of prednisolone equivalent dose 10mg or more for more than 3 months

4. Known history or active infective endocarditis

5. On peritoneal dialysis or haemodialysis

6. Documented pregnancy

Substudy 2

Inclusion Criteria:

1. Age 65 years and above
2. Written informed consents obtained

Exclusion Criteria:

1. Known history of confirmed COVID-19 infection

2. Known active sepsis or active malignancy

3. Known increased infection risk due to underlying immunosuppressed state which includes:

   • Prior organ or hematopoietic stem cell transplant
   • Neutropenia with absolute neutrophil count (ANC) <500 cells/ul at the time of study inclusion
   • Known HIV infection with CD4 <200 cells/ul at the time of study inclusion
   • On concomitant immunosuppressants, chemotherapies or corticosteroid at a dose of prednisolone equivalent dose 10mg or more for more than 3 months

4. Known history or active infective endocarditis

5. On peritoneal dialysis or haemodialysis

6. Known active malignancy

7. Known terminal illness with life expectancy less than 3 months