Young infants exhibit robust functional antibody responses and restrained IFN-γ production to SARS-CoV-2

Area of Science:

• Immunology
• Pediatrics
• Virology

Background:

• Severe COVID-19 is unexpectedly rare in infants, despite their vulnerability to other respiratory viruses.
• Understanding infant immune responses to SARS-CoV-2 is crucial for explaining this observation.

Purpose of the Study:

• To evaluate the convalescent immune responses in infants recovered from COVID-19.
• To compare infant immune profiles with those of their parents and adult COVID-19 survivors.

Main Methods:

• Analysis of serum and saliva antibody levels (IgG, IgA) against SARS-CoV-2 spike protein.
• Assessment of antibody-mediated viral entry blocking.
• Measurement of cytokine production (IFN-γ, TNF-α) by peripheral blood mononuclear cells.
• Principal-component analysis of immune response data.

Main Results:

• Infants exhibited high serum IgG and IgA levels to SARS-CoV-2 spike protein with functional viral entry blocking capacity.
• Robust saliva anti-spike IgG and IgA responses were observed in infants.
• Spike-specific IFN-γ production was restrained in infant PBMCs, but T-cell frequency producing IFN-γ/TNF-α was comparable to adults.
• Infant immune responses were distinct from parental responses via principal-component analysis.

Conclusions:

• Robust functional antibody responses in infants may contribute to protection against severe COVID-19.
• A combination of high antibody levels and potentially modulated T-cell responses could explain the rarity of severe disease in this age group.