In general, both mRNA-1273 ID or IM vaccination generated higher PVNT50 against Wuhan than ID or IM vaccination of BNT162b2 (< .005 for the comparisons of the same route), and ID mRNA-1273 experienced similar GMT to IM BNT162b2 (= .577). IM groups. ID route tended to have fewer systemic adverse events (AEs), although more local AEs were reported in the ID mRNA-1273 group. Conclusions Fractional ID vaccination induced lower humoral but comparable cellular immunity compared to IM and may be an alternative for older people. Clinical Trials Registration TCTR20220112002. Keywords: COVID-19 booster vaccination, immune responses, intradermal, mRNA vaccines, older adults In this randomized controlled trial in elderly, fractional intradermal COVID-19 booster vaccination with BNT162b2 or mRNA-1273 induced lower antibody but comparable cellular immune response compared with INT-777 standard intramuscular vaccination. Intradermal route induced relatively fewer systemic but more local adverse events. Coronavirus disease 2019 (COVID-19) booster vaccination has been found to improve protection against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, including the Omicron variants [1C4]. The booster vaccination has been recommended for older adults due to their aging immune system (immunosenescence) INT-777 as well as the likelihood of having comorbidities that predispose them to severe COVID-19. However, the booster vaccine protection among older Thai adults was reported recently at 44% (unpublished statement by the Ministry of General public Health), which is usually relatively low but much like other settings, which could partly be attributed to vaccine hesitancy regarding adverse effects following messenger RNA (mRNA) vaccination [2]. Intradermal (ID) vaccination of BCG and rabies vaccines have been given routinely in many settings. The dermis and epidermis layers are rich in antigen-presenting cells, and lower or fractional dosage of vaccine content are normally administered intradermally. ID administration for other vaccines such as inactivated polio, hepatitis B, and influenza vaccines given at fractional dose is found to induce comparative (or higher) immunogenicity and comparable safety profiles INT-777 compared to intramuscular (IM) or subcutaneous (SC) vaccination [5, 6]. Hence, COVID-19 vaccination via the ID route may be considered as an alternative to IM vaccination. This would be particularly relevant in the context of limited COVID-19 vaccine materials [7]. Moreover, this option route using lower amount of mRNA vaccine could reduce adverse effects and may increase acceptance of these vaccines. You will find limited studies on COVID-19 vaccination given via the ID route. Most studies were conducted in healthy adults and found that ID vaccination induced comparable or slightly lower immune responses than IM, but with fewer systemic adverse events (AEs) [8, 9]. Older adults have different immune composition under the skin and may respond to ID route differently. This study aims to compare the immunogenicity and reactogenicity of fractional-dose mRNA-1273 (Moderna) and BNT162b2 (Pfizer) booster vaccination given via ID route with standard-dose mRNA-1273 and BNT162b2 given via IM route in older adults previously vaccinated with 2 doses of ChAdOx1 (AstraZeneca). MATERIALS AND METHODS This open-label study was conducted at a single-center, tertiary hospital in Bangkok, Thailand, during the period of JanuaryCJune 2022. Eligible subjects were individuals aged 65 years Rabbit monoclonal to IgG (H+L)(HRPO) who have primarily received 2 doses of IM ChAdOx1 series 12C24 weeks earlier. Exclusion criteria included any previous infections of SARS-CoV-2, acute illness or inflammation, history of anaphylaxis to any vaccination or drugs, receipt of any vaccination within 2 previous weeks, and receipt of any immunosuppressants or in the state of immunosuppression. Patients and their caretakers were informed of the benefits granted by joining the study (ie, immunization as per national guidelines recommendation against COVID-19) as INT-777 well as its risks (ie, novelty from current requirements vaccination) before written informed consent was obtained. The participants were INT-777 randomized to 1 1 of the 4 vaccination groups: ID mRNA-1273 (20 g; 0.1 mL; n = 35), IM mRNA-1273 (100 g; 0.5 mL; n = 35), ID BNT162b2 (10 g; 0.1 mL; n = 35 for each group of 65?79 and 80 years of age) or IM BNT162b2 (30 g; 0.3 mL; n = 35 for each group of.