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1.
Vaccines (Basel) ; 10(9)2022 Sep 07.
Article in English | MEDLINE | ID: covidwho-2010361

ABSTRACT

A practical booster vaccine is urgently needed to control the coronavirus disease (COVID-19) pandemic. We have previously reported the safety and immunogenicity of a fractional intradermal booster, using the BNT162b2 mRNA vaccine in healthy volunteers who had completed two doses of inactivated SARS-CoV-2 vaccine. In this study, an intramuscular booster at full dosage was used as a control, and a half-dose vaccination was included for reciprocal comparison. Detailed T-cell studies are essential to understand cellular responses to vaccination. T-cell immunity was examined using S1 peptide restimulation and flow cytometry. The fractional dose (1:5) of the BNT162b2 mRNA vaccine enhanced antigen-specific effector T-cells, but the responses were less remarkable compared to the intramuscular booster at full dosage. However, the intradermal regimen was not inferior to the intramuscular booster a month after boosting. An intradermal booster using only one-fifth of the standard dosage could provide comparable T-cell responses with the fractional intramuscular booster. This work confirms the efficacy of intradermal and fractional vaccination in terms of T-cell immunogenicity in previously immunised populations.

2.
Vaccines (Basel) ; 9(12)2021 Nov 23.
Article in English | MEDLINE | ID: covidwho-1542808

ABSTRACT

Effective vaccine coverage is urgently needed to tackle the COVID-19 pandemic. Inactivated vaccines have been introduced in many countries for emergency usage, but have only provided limited protection. Heterologous vaccination is a promising strategy to maximise vaccine immunogenicity. Here, we conducted a phase I, randomised control trial to observe the safety and immunogenicity after an intradermal boost, using a fractional dosage (1:5) of BNT162b2 mRNA vaccine in healthy participants in Songkhla, Thailand. In total, 91 volunteers who had been administered with two doses of inactivated SARS-CoV-2 (CoronaVac) were recruited into the study, and then randomised (1:1:1) to received different regimens of the third dose. An intramuscular booster with a full dose of BNT162b2 was included as a conventional control, and a half dose group was included as reciprocal comparator. Both, immediate and delayed adverse events following immunisation (AEFI) were monitored. Humoral and cellular immune responses were examined to observe the booster effects. The intradermal booster provided significantly fewer systemic side effects, from 70% down to 19.4% (p < 0.001); however, they were comparable to local reactions with the conventional intramuscular booster. In the intradermal group after receiving only one fifth of the conventional dosage, serum Anti-RBD IgG was halved compared to the full dose of an intramuscular injection. However, the neutralising function against the Delta strain remained intact. T cell responses were also less effective in the intradermal group compared to the intramuscular booster. Together, the intradermal booster, using a fractional dose of BNT162b2, can reduce systemic reactions and provides a good level and function of antibody responses compared to the conventional booster. This favourable intradermal boosting strategy provides a suitable alternative for vaccines and effective vaccine management to increase the coverage during the vaccine shortage.

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