Intradermal Fractional ChAdOx1 nCoV-19 Booster Vaccine Induces Memory T Cells: A Follow-Up Study

Area of Science:

• Immunology
• Vaccinology
• Infectious Disease

Background:

• Booster vaccination with viral vector and mRNA platforms elicits robust humoral and cellular immune responses.
• Intradermal (ID) vaccination strategies are being explored as alternatives to intramuscular (IM) delivery.
• Understanding T cell kinetics and phenotypes post-booster vaccination is crucial for optimizing vaccine efficacy.

Purpose of the Study:

• To quantify and compare T cell responses following booster vaccination with viral vector (ChAdOx1 nCoV-19) and mRNA vaccines.
• To evaluate the immunogenicity of fractional ID vaccination versus standard IM delivery.
• To assess the durability of T cell responses at three months post-vaccination.

Main Methods:

• Quantification of T cell responses, including CD8+ T cell counts and cytokine production.
• Comparison of immune responses elicited by ID fractional dose versus IM booster vaccination.
• Analysis of effector memory T cell phenotypes.

Main Results:

• ChAdOx1 nCoV-19 vaccination led to higher S1-specific CD8+ memory T cell numbers compared to antibody responses.
• Effector memory T cell phenotypes were similar between mRNA and viral vector vaccine boosters.
• Detectable cytokine responses persisted three months post-vaccination for both vaccine types.
• Fractional ID ChAdOx1 nCoV-19 vaccination induced greater effector CD8+ T cell responses than IM vaccination.

Conclusions:

• Dose-reduction vaccination strategies utilizing intradermal delivery effectively stimulate effector memory T cell responses.
• Intradermal injection represents a promising approach for enhancing vaccine program effectiveness.
• Both viral vector and mRNA vaccines induce durable T cell immunity, with ID delivery showing potential advantages for certain vaccines.