Inorganic nitrate can protect blood vessels from the damage that occurs during cardiovascular disease. Early experimental work suggests that nitrate-induced improvements in vascular function relate to the suppression of inflammatory pathways. Whether this protection against inflammation-induced damage to the blood vessel wall might also be functional in the setting of COVID-19 vaccination will be investigated.

Vascular function will be assessed before and after the healthy participant has received their COVID-19-vaccination. Whether there might be differences in the response to the vaccine between the sexes and whether a dietary nitrate intervention impacts upon the effects of vaccination will be investigated.

The study is in two parts:

Part A: To assess sex differences in the vascular response to COVID-19 vaccination.

Part B: To assess whether inorganic nitrate, in the form of dietary inorganic nitrate supplementation compared to placebo control, can raise circulating plasma nitrite levels and thereby prevent the systemic inflammation that causes vascular dysfunction.

Whether the COVID-19 vaccine can be used to study endothelial dysfunction and whether inorganic nitrate might be useful in restoring the function of the endothelium in a scenario simulating the COVID-19 infection setting will be investigated.

Furthermore, sex differences in the vascular response to the COVID-19 vaccination will be investigated.

Design: A prospective randomised, double-blind, placebo-controlled trial.

Target population: A total of 98 healthy participants will be recruited. Part A: 30 participants (15 male, 15 female.) Part B: 68 participants (34 intervention, 34 placebo). Participants will be recruited prior to receiving the COVID-19 vaccination, via Barts Health NHS Trust approved vaccination hubs.

Setting: Equal numbers of healthy male and female volunteers, aged between 18 and 60 years of age, will be recruited. Following recruitment, participants will undergo baseline measurements of vascular function of flow mediated dilatation (FMD) and pulse wave analysis/velocity (PWA, PWV), in addition to haematological and clinical biochemical analyses. Volunteers will then be randomised into one of the 2 study Parts (Part A: sex differences in vascular response to COVID-19 vaccine, Part B: influence of dietary nitrate upon vascular responses to COVID-19 vaccine). If randomised to Part B, volunteers will be treated with 3 days of either 4-5mmol nitrate-containing beetroot juice or placebo. If randomised to Part A, the volunteers will not receive an intervention. On day 3, all participants will receive their COVID-19 vaccine. At 8±2hours after the vaccine, the participants will undergo repeat measurements of vascular function. A quality of life questionnaire will be obtained 28 days after the vaccine has been administered.

Intervention: All volunteers will receive COVID-19 vaccination in Part A and Part B. In Part B of the study, volunteers will be randomised in a 1:1 fashion to receive either nitrate-containing beetroot juice (4-5mmol nitrate) or nitrate-deplete placebo.

The study will take place in the Clinical Research Centre at The William Harvey Research Institute.

Analysis: For the analysis of Part A linear regression will be used to compare change in vascular dysfunction from pre- to post-vaccination between the sexes, unadjusted and adjusted for important risk factors including age, BMI and baseline vessel diameter. For Part B analysis of covariance (ANCOVA) will be used to compare change in vascular dysfunction from pre- to post-vaccination between dietary nitrate and placebo control groups adjusting for pre-vaccination level, and to compare change in plasma nitrite between dietary nitrate and placebo control groups adjusting for baseline nitrite level.

Inclusion Criteria:

1. Healthy volunteers with a booking for COVID-19 vaccination slot as per government guidelines
2. Aged 18-60
3. Volunteers who are willing to sign the consent form

Exclusion Criteria:

1. Aged <18 or >60 years
2. Healthy subjects unwilling to consent
3. Pregnant, or any possibility that a subject may be pregnant
4. History of any serious illnesses, including recent infections or trauma
5. Subjects taking systemic medication (other than the oral contraceptive pill)
6. Subjects with self-reported use of mouthwash or tongue scrapes
7. Subjects with recent (2 weeks) or current antibiotic use
8. Subjects with a history, or recent treatment of (within last 3 months) any oral condition (excluding caries), including gingivitis, periodontitis and halitosis
9. Subjects with a history of COVID-19 vaccination
10. Subjects with any history of a blood-borne infectious