Seroprevalence of SARS-Cov-2 IgG antibodies in patients at a single center in Saudi Arabia.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has had a massive impact on public health as well as the economy. Understanding the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among undiagnosed individuals is important for developing an informed pandemic response. OBJECTIVE: Investigate the prevalence of undiagnosed COVID-19 disease. DESIGN: Cross-sectional. SETTING: Tertiary care center in Madinah, Saudi Arabia. SUBJECTS AND METHODS: All participants were on follow-up visits to various clinics and had not been previously diagnosed with COVID-19. Enzyme-linked immunosorbent assay was used to specifically assess the anti-spike IgG antibody seropositivity in serum samples. We associated the seropositivity rates of the participants with age, body mass index (BMI), nationality, blood groups, and sex with uni- and multivariate analyses. MAIN OUTCOME MEASURES: Seropositivity for IgG anti-spike antibodies against SARS-CoV-2. SAMPLE SIZE AND CHARACTERISTICS: 527 subjects, with a median (interquartile percentiles) age of the 527 subjects was 34 (24-41). RESULTS: Of the 527 samples, about one-fourth (n=124, 23.5%) were positive for anti-spike IgG antibody against SARS CoV-2. Age was associated with anti-spike IgG antibody positivity (P<.002). Participants >30 years were more likely to be seropositive (28-29%) than younger participants (15.4%). Additionally, seropositivity was associated with female gender (P<.001) and a higher BMI (P<.006). In the multivariate logistic regression, age >30, female gender and BMI >40 were associated with seropositivity. CONCLUSION: The percentage of seropositive individuals reflects the high level of undiagnosed COVID-19 patients among the population. Our results will help in a better evaluation of the public health measures applied during the COVID-19 pandemic and any future public health crises. LIMITATIONS: Sample size was small, single-center study and no rural areas were included. CONFLICT OF INTEREST: None.

A Single Dose of SARS-CoV-2 Vaccine Primes a Strong Humoral Immune Response in COVID-19-Recovered Patients.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes coronavirus disease 2019 (COVID-19), which has affected hundreds of millions of people globally. The development of safe and effective vaccines represents an urgent demand. A total of 136 participants were recruited in this study, including 75 men and 61 women. The participants were divided into two groups: those who were virus naïve (never infected) and those who had recovered from COVID-19. Each group included individuals who received either the Pfizer-BioNTech BNT162b2 mRNA or the Oxford-AstraZeneca ChAdOx1 COVID-19 vaccine. Enzyme-linked immunosorbent assay (ELISA) was used to measure anti-S IgG antibody concentrations in sequential serum samples obtained before vaccine administration, after the first vaccine dose, and after the second vaccine dose. We compared the antibody responses of individuals with confirmed prior COVID-19 infection with those of individuals without prior evidence of infection. All participants who were previously infected with SARS-CoV-2 who received one dose of either the Pfizer-BioNTech BNT162b2 mRNA or the Oxford-AstraZeneca ChAdOx1 COVID-19 vaccine showed significant anti-S IgG antibody levels. No sex-related differences were observed when we compared antibody levels between men and women. In infection-naïve participants ≥60 years, a second vaccine dose was necessary to achieve higher levels of antibody when comparing the IgG antibody levels after receiving the first and second dose.