Background: The dynamics of SARS-CoV-2 alpha variant shedding and immune responses at the nasal mucosa remain poorly characterised.

Methods: We measured infectious viral release, antibodies and cytokines in 426 PCR+ nasopharyngeal swabs from individuals harboring non-alpha or alpha variants.

Findings: With both lineages, viral titers were variable, ranging from 0 to >106 infectious units. Rapid antigenic diagnostic tests were positive in 94% of samples with infectious virus. 68 % of individuals carried infectious virus within two days after onset of symptoms. This proportion decreased overtime. Viable virus was detected up to 14 days. Samples containing anti-spike IgG or IgA did not generally harbor infectious virus. Ct values were slightly but not significantly lower with alpha. This variant was characterized by a fast decrease of infectivity overtime and a marked release of 13 cytokines (including IFN-b, IP-10 and IL-10).

Interpretation: The alpha variant displays modified viral decay and cytokine profiles at the nasopharyngeal mucosae during symptomatic infection.

Funding: This retrospective study has been funded by Institut Pasteur, ANRS, Vaccine Research Institute, Labex IBEID, ANR/FRM and IDISCOVR, Fondation pour la Recherche Médicale.