Kinetics of specific anti-SARS-CoV-2 IgM, IgA, and IgG responses during the first 12 months after SARS-CoV-2 infection: A prospective longitudinal study.

Coronavirus 2019 (COVID-19) is a global health threat. The kinetics of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) need to be assessed, as the long-term duration of these immunoglobulins remains largely controversial. The aim of this study was to assess the longitudinal dynamics of anti-SARS-CoV-2 antibodies against the nucleocapsid (N) protein and the receptor-binding domain (RBD) of the spike protein up to one year in a cohort of 190 COVID-19 patients. Between March and September 2021, we enrolled patients from two regional hospitals in Casablanca, Morocco. Blood samples were collected and analyzed for antibody levels. We used the commercial Euroimmun ELISA for the determination of anti-N IgM, the Abbott Architect™ SARS-CoV-2 IgG test for the detection of anti-RBD IgG, and an in-house kit for the assay of anti-N IgG and anti-N IgA. IgM and IgA antibodies were assessed 2-5, 9-12, 17-20 and 32-37 days after symptom onset. IgG antibodies were also assessed 60, 90, 120 and 360 days after symptom onset. One-third of patients developed IgM (32%), while two-thirds developed IgA (61%). One month of symptom onset, most patients developed IgG, with 97% and 93% positivity for anti-RBD IgG and anti-N IgG, respectively. The anti-RBD IgG positivity rate remained high up to one year of follow-up. However, the anti-N IgG positivity rate decreased over time, with only 41% of patients testing positive after one year's follow-up. IgG levels were significantly higher in older people (over 50 years) than in other study participants. We also found that patients who had received two doses of ChAdOx1 nCoV-19 vaccine prior to infection had a lower IgM response than unvaccinated patients. This difference was statistically significant two weeks after the onset of symptoms. We present the first study in Africa to measure the kinetics of antibody response (IgA, IgM and IgG) to SARS-CoV-2 over one year. Most participants remained seropositive for anti-RBD IgG after one year but showed a significant decline in antibody titers.

Mix-and-match COVID-19 vaccines trigger high antibody response after the third dose vaccine in Moroccan health care workers.

Recent studies have shown that in individuals who have received two doses of COVID-19 vaccine, the level of IgG antibodies decreased over time. In addition, the resurgence of the epidemic due to variants has led the authorities in several countries, including Morocco, to extend the third dose to the entire adult population. In this study, we included 43 healthcare workers (HCWs) who were vaccinated with three doses. They were vaccinated with ChAdOx1 nCoV-19 for the first two doses and with BNT 162b2 or BBIBP-CorV vaccine for the third dose. Humoral response was assessed on the day of injection of the third dose of vaccine and one month after the third dose by measuring anti-receptor-binding domain (RBD) IgG levels. Seven months after the second dose, the median titer of anti-RBD IgG was higher in the group with a history of SARS-CoV-2 infection than in the group with no history of infection (1038 AU/mL vs. 76.05 AU/mL, respectively, p = 0.003). One month after the third dose, a significant increase in median level of anti-RBD in both groups was observed: from 76.05 AU/mL to 6127 AU/mL in the group with no history of infection and from 1038 AU/mL to 14,412 AU/mL in the group with history of infection. Notably, the BNT 162b2 vaccine elicits a high titer of anti-RBD antibody compared to the BBIBP-CorV vaccine. Median antibody titers were 21,991 AU/mL and 3640 AU/mL for BNT 162b2 and BBIBP-CorV vaccines, respectively (p = 0.0002). 23% of HCWs were infected with SARS-CoV-2 within the first two months after the third dose injection. However, all these patients developed mild symptoms and tested negative by RT-qPCR between 10 and 15 days after the onset of symptoms. Our findings support that the third dose of COVID-19 vaccine significantly improves the humoral response and protects against the severe disease.

Development and comparative evaluation of SARS-CoV-2 S-RBD and N based ELISA tests in various African endemic settings.

Management of the COVID-19 pandemic relies on molecular diagnostic methods supported by serological tools. Herein, we developed S-RBD- and N- based ELISA assays useful for infection rate surveillance as well as the follow-up of acquired protective immunity against SARS-CoV-2. ELISA assays were optimized using COVID-19 Tunisian patients' sera and prepandemic controls. Assays were further validated in 3 African countries with variable endemic settings. The receiver operating curve was used to evaluate the assay performances. The N- and S-RBD-based ELISA assays performances, in Tunisia, were very high (AUC: 0.966 and 0.98, respectively, p < 0.0001). Cross-validation analysis showed similar performances in different settings. Cross-reactivity, with malaria infection, against viral antigens, was noticed. In head-to-head comparisons with different commercial assays, the developed assays showed high agreement. This study demonstrates, the added value of the developed serological assays in low-income countries, particularly in ethnically diverse populations with variable exposure to local endemic infectious diseases.