Increasing Levels of Serum Anti-Spike S1-RBD IgG after 120 Days of the Pfizer-BioNTech-mRNA Second Dose Vaccination

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccines, such as Pfizer-BioNTech, have demonstrated high efficacy; however, there is limited data on the duration of immune responses besides their relationships with age, gender, body mass index (BMI), and the presence of previous coronavirus disease-2019 (COVID-19) infection. This study aimed to evaluate SARS-COVID-19 Anti-Spike IgG levels after 30 days (one month) and 120 days (four months) of the 2^nd dose of Pfizer-BioNTech vaccine given to medical students at Al-Iraqi University, Baghdad, Iraq. This study was performed after the obtainment of the acceptance and approval of the Medical College of Al-Iraqi University and the Iraqi Ministry of Health. Two groups of students were randomly picked up from the Medical College of Al-Iraqi University. They were completely vaccinated by administering two doses of Pfizer-BioNTech/0.5 ml for each dose. After taking their permission, 5 ml of their blood (one group after one month and the second group after four months of vaccination) was drawn in the Higher Education lab inside the Medical College of Al-Iraqi University. It took approximately four months to collect the samples (from October 2021 until February 2022). Following that, serological analysis was done for measuring the SARS-CoV-2 spike protein IgG by using Elabscience/SARS-CoV-2 spike protein IgG ELISA Kit (USA) (+ve <0.06) that was performed in the Higher Education lab of Medical College of Al-Iraqi University. Demographic data were also collected from participants, including age, gender, BMI, blood group, and the presence of previous COVID-19 infection. For statistical analysis, SPSS (version 26) and STATISTICA (version 12) were used to input, check, and analyze data. Standard approaches of frequencies and percentages were used for qualitative variables, while for quantitative variables, mean±standard deviation was used. A P-value of <0.05 was considered a significant plasma level of the SARS-COVID-19 Anti-Spike IgG. The study results showed that in group 1 (after one month of the 2^nd dose), the male-female ratio was 62.2: 37.8, the mean age of the vaccinated students was 28.2000 years old, and the BMI was 25.5454 kg/m2 with 33.3% previously COVID-19 infected individuals. In group 2 (after four months of the 2^nd dose), the male-female ratio was 44.4: 55.6, the mean age of the vaccinated students was 25.8444 years old , and the BMI was 24.7584 kg/m2 with 24.4% previously COVID-19 infected individuals. The plasma levels of SARS-COVID-19 Anti-Spike IgG after the 2^nd dose of the Pfizer-BioNTech vaccine in group 1 (one month) and group 2 (four months) were statistically non-parametric. Once the independent two samples Mann-Whitney test was used, a significant difference (P<0.05) was observed in SARS-COVID-19 Anti-Spike IgG plasma levels after 30 days of the 2^nd dose of the Pfizer-BioNTech vaccine administration, compared to the 120 days of administration. In conclusion, SARS-COVID-19 Anti-Spike IgG levels significantly increased in group 2 (four months after the 2^nd dose of the Pfizer-BioNTech vaccine), compared to group 1 (one month after the 2^nd dose of the Pfizer-BioNTech vaccine).