Do the Moderna and Pfizer COVID-19 vaccines elicit different antibody responses?
A recent study led by scientists from the United States has compared the anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody response among clinicians who have been immunized with Pfizer/BioNTech or Moderna coronavirus disease 2019 (COVID-19) vaccine. The findings reveal that the Moderna vaccine induces higher and faster antibody responses than the Pfizer/BioNTech vaccine. A detailed description of the study, which is not yet peer-reviewed, is currently available on the bioRxiv* preprint server. Background  By virtue of significant efforts made by the global scientific community, it has become possible to develop potential COVID-19 vaccines within one year of the emergence of the highly pathogenic SARS-CoV-2. In the United States, two mRNA-based COVID-19 vaccines, namely BNT162b2 (Pfizer/BioNTech) and mRNA-1273 (Moderna), have received emergency use approval from the US Food and Drug Administration (FDA). These vaccines have shown more than 90% efficacy in preventing SARS-CoV-2 infection and symptomatic COVID-19 in human clinical trials as well as in real-world pandemic situations. In the BNT162b2 vaccine, 30 g of prefusion-stabilized full-length SARS-CoV-2 spike protein is used as a vaccine immunogen. Similarly, in the mRNA-1273 vaccine, 100 g of prefusion-stabilized spike protein is used as a vaccine immunogen. Regarding standard vaccination regimen, two doses of BNT162b2 or mRNA-1273 vaccine are administered at an interval of 3 or 4 weeks, respectively. In the current study, the scientists have evaluated antibody responses to SARS-CoV-2 among individuals who have been immunized with either BNT162b2 or mRNA-1273. Study design  A total of 611 clinicians were enrolled in the study. The average age of participants was 47 years (age range: 28  76 years). In addition, about 67% of participants were female, and 33% were male. During the entire study period, the participants provided serum samples at baseline and every three months. The seropositive or negative status of each participant was assessed by measuring serum levels of IgG-specific anti-SARS-CoV-2 spike receptor-binding domain (RBD) antibodies. In the study, enzyme-linked fluorescent assay used for serological testing has 100% specificity and selectivity for SARS-CoV-2 specific antibodies. Important observations  About 90% of participants (551 out of 611) completed the 3-month follow-up. At baseline, 532 out of 551 participants were seronegative for anti-SARS-CoV-2 antibodies. Among the final cohort of 532 participants who were eligible for seroconversion, 217 were immunized with the BNT162b2 vaccine, and 315 were immunized with the mRNA-1273 vaccine. The serological findings revealed that 530 out of 532 participants developed anti-SARS-CoV-2 antibodies following 2-dose vaccination. Among 2 participants who did not develop antibodies following vaccination with BNT162b2 or mRNA-1273, one was receiving a monoclonal antibody against B cell antigen CD20, and the other one was receiving an immunomodulatory drug that sequesters lymphocytes in lymph nodes. The statistical analyses conducted after adjusting for age and gender revealed that compared to the 1st vaccine dose, the 2nd dose elicited significantly higher antibody response in all participants. For both vaccines, the highest antibody titers were achieved after 6 weeks of immunization. Interestingly, significant variation in antibody response was observed among participants who received BNT162b2 or mRNA-1273. Specifically, higher antibody titers were observed in mRNA-1273-vaccinated participants on days 14-20, 42-48, 70-76, and 77-83. In contrast, BNT162b2-vaccinated participants exhibited higher antibody titers on days 28-34. Regarding early antibody response, 2 out of 44 mRNA-1273-vaccinated participants displayed detectable antibody levels within 6 days following the 1st vaccine dose. However, BNT162b2 failed to induce any antibody response during the same period. Study significance  The study reveals that the mRNA-1273 vaccine is capable of inducing a more robust and faster antibody response than the BNT162b2 vaccine. However, the scientists mention that the difference in antibody response could be due to significantly higher amounts of vaccine immunogen used in the mRNA-1273 vaccine than BNT162b2. Moreover, comparatively wider protection observed for mRNA-1273 may be because of the longer dose interval compared to that of BNT162b2. *Important notice  bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.