Detection of salivary IgA among recovered COVID-19 Patients and non-infected subjects after the first dose of vaccination

Introduction: Mucosal immunity, including secretory IgA plays a vital role in host defence against respiratory pathogens, including SARS-CoV-2. Therefore, this study aims to analyse salivary IgA in response to the COVID-19 vaccines such as BNT162b2, CoronaVac, and AZD1222 in convalescents (RT-PCR-confirmed COVID-19) and naive subjects (non-infected COVID- 19) before receiving their second dose. Material(s) and Method(s): Saliva was collected in a sterile container, centrifuged and stored at -80 degreeC until analysis. Salivary IgA was detected using an Anti-SARS-CoV-2 ELISA (IgA) kit (Euroimun-Lubeck, Germany). Result(s) and Conclusion(s): The study involved 281 participants, with 145 convalescents and 136 naive subjects. Before receiving the first dose of the COVID-19 vaccine, 81.4%, 15.2%, and 3.4% of the 145 convalescents had positive, negative, and borderline results, respectively. Then, before receiving the second dose, 100% positive results were observed with the salivary IgA ratio median of 4.95, 2.71 and 3.32 among BNT162b2, CoronaVac and AZD1222, respectively. There was evidence of a difference in salivary IgA ratio between BNT162b2, AZD1222 and CoronaVac (p < 0.005). However, there was no evidence of a difference in salivary IgA ratio between CoronaVac and AZD1222. For naive subjects, 95.7%, 30.2% and 83.0% showed positive results before receiving the second dose of BNT162b2, CoronaVac and AZD1222, with the salivary IgA ratio median of 1.63, 0.74 and 1.43, respectively. There was evidence of a difference in saliva IgA ratio between BNT162b2 and CoronaVac as well as AZD1222 and CoronaVac (p < 0.005). However, no significant difference was observed between BNT162b2 and AZD1222. After the first dose of vaccination, the vaccines significantly increased the production of salivary IgA in convalescent compared to naive subjects.

Persistent B cell memory after SARS-CoV-2 vaccination is functional during breakthrough infections.

Breakthrough SARS-CoV-2 infections in fully vaccinated individuals are considered a consequence of waning immunity. Serum antibodies represent the most measurable outcome of vaccine-induced B cell memory. When antibodies decline, memory B cells are expected to persist and perform their function, preventing clinical disease. We investigated whether BNT162b2 mRNA vaccine induces durable and functional B cell memory in vivo against SARS-CoV-2 3, 6, and 9 months after the second dose in a cohort of health care workers (HCWs). While we observed physiological decline of SARS-CoV-2-specific antibodies, memory B cells persist and increase until 9 months after immunization. HCWs with breakthrough infections had no signs of waning immunity. In 3-4 days, memory B cells responded to SARS-CoV-2 infection by producing high levels of specific antibodies in the serum and anti-Spike IgA in the saliva. Antibodies to the viral nucleoprotein were produced with the slow kinetics typical of the response to a novel antigen.

SARS-CoV-2 identification and IgA antibodies in saliva: One sample two tests approach for diagnosis.

AIM: This study aims to verify whether standardized saliva collection is suitable for SARS-CoV-2 molecular detection and IgA measurement. METHODS: 43 COVID-19 inpatients and 326 screening subjects underwent naso-pharyngeal (NP)-swab and saliva collection (Salivette). Inpatients also underwent repeated blood collections to evaluate inflammation and organs involvement. In all patients and subjects, SARS-CoV-2 (gene E) rRT-PCR was undertaken in saliva and NP-swabs. Salivary IgA and serum IgA, IgG, IgM were measured on inpatients' samples. RESULTS: NP-swabs and saliva were both SARS-CoV-2 positive in 7 (16%) or both negative in 35 (82%) out of 43 patients successfully included in the study. NP-swabs and saliva results did not perfectly match in one patient (saliva positive, NP-swab negative). Positive molecular results were significantly associated with disease duration (p = 0.0049). 326/326 screening subjects were SARS-CoV-2 negative on both NP-swabs and saliva. Among the 27 saliva samples tested for IgA, 18 were IgA positive. Salivary IgA positivity was associated with pneumonia (p = 0.002) and CRP values (p = 0.0183), not with other clinical and molecular data, or with serum immunoglubulins. CONCLUSIONS: A standardized saliva collection can be adopted to detect SARS-CoV-2 infection in alternative to NP-swabs. Preliminary data on salivary IgA support the use of saliva also for patient monitoring.