A comparison between Pfizer/BioNTech's and Sinopharm's SARS-CoV-2 vaccines

The coronavirus disease 2019 (COVID-19), which is caused by infection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to affect the wellbeing and quality of life of people worldwide. Several different COVID-19 vaccines are currently available to combat this pandemic, some of which include messenger ribonucleic acid (mRNA) vaccines and classic inactivated virus vaccines.

Study: Pfizer-BioNTech and Sinopharm: A Comparative Study on Post-Vaccination Antibody Titers. Image Credit: MR.AUKID PHUMSIRICHAT / Shutterstock.com

Background

All COVID-19 vaccines act by activating the innate and adaptive immune responses. Adaptive immunity involves the activation of B-cells, which multiply and increase in response to vaccines to ultimately support the production of antibodies.

Most COVID-19 vaccines are designed to elicit spike protein-specific antibodies, as these have been reported to be effective in combating the disease. Further, anti‐spike protein receptor-binding domain (anti‐S‐RBD) immunoglobulin G (IgG) levels play a role in determining immunity to SARS-CoV-2. The antibody titers elicited by COVID-19 vaccines can be measured using serological diagnostic tests.

In a recent study published in the journal vaccines, researchers compare antibody titers elicited by the Pfizer‐BioNTech mRNA vaccine and the classic inactivated virus vaccine Sinopharm in order to identify the most effective vaccine. This study explored both IgM and IgG antibody titers; however, the researchers concentrated more on IgG, as it has been reported to be the most prevalent antibody in human plasma that plays a role in long-term immunity conferred by vaccinations. The findings from this study may help enhance the existing vaccine therapies for COVID-19.

Study design

The current study was performed on Jordanian adults and was conducted between March and April 2021 as a prospective observational cohort study. The participants consisted of individuals who had received two doses of either Sinopharm or Pfizer‐BioNTech COVID‐19 vaccines, with an interval of 21 days. All participants were enrolled in the study six weeks after the second dose.

IgG and IgM levels in human serum or plasma specific for SARS‐CoV‐2 were measured using Vitek Immuno Diagnostic Assay Systems, which is an enzyme-linked immunosorbent assay (ELISA).

Pfizer‐BioNTech performs better than Sinopharm

The group of participants receiving either Pfizer‐BioNTech or Sinopharm vaccines was compared based on demographic characteristics, past medical history, and prior COVID-19 infections.

A total of 141 participants received the Pfizer‐BioNTech COVID‐19 vaccine, of which 93% exhibited positive IgG titers. Comparatively, 147 received the Sinopharm vaccine, of which 85.7% showed positive IgG titers.

The mean titer for IgG amongst the Pfizer‐BioNTech vaccine group was 515.5 ± 1143.5 BAU/mL, and the Sinopharm vaccine group was 170.0 ± 230.0 BAU/mL. No statistically significant difference was observed in IgG positivity or IgM titers between the two vaccine groups.

Age-related differences were apparent between individuals in the IgG positive and negative groups, with 86.4% of those with negative IgG titers aged more than 60 years. Among the subjects who were administered the Sinopharm vaccine, 90.5% of those with negative titers were aged more than 60 years, whereas 9.5% were between 40-60 years old.

Notably, only one subject in the 20-40 year age group showed negative IgG titers amongst the Pfizer-BioNTech group. Further, it was observed that 54.5% of subjects who had negative IgG titers had diabetes and 40.9% were suffering from cardiovascular or cerebrovascular diseases.

IgM titer positive and negative groups of individuals were also compared six weeks after vaccination based on characteristics like age, gender, body mass index (BMI), smoking habits, and positivity for IgG titers. These groups exhibited significant differences in mean IgM and IgG titer values.

Multivariable regression analysis was performed, which revealed that Pfizer‐BioNTech vaccine administration had a statistically significant positive effect on IgG titer positivity. Comparatively, the presence of cardiovascular diseases had a statistically significant negative effect.

Study limitations

The study had certain limitations. Samples were collected from the study subjects only at a single time point of six weeks post-vaccination, which prevented the possibility of exploring antibody or immunity decay.

Though the VIDAS diagnostic test was reported to have a sensitivity of 88.3% and specificity of 98.4%, there is a possibility that it may not have accurately estimated the antibody titers. The test reliability may also be compromised due to cross-reactivity between the SARS‐CoV‐2‐specific antibodies and endemic coronaviruses.

Implications

The present study compared the efficiency of the Pfizer‐BioNTech mRNA vaccine to a classic vaccine Sinopharm. In diagnostic assays, the Pfizer BioNTech elicited high IgG titers levels when compared to Sinopharm.

Furthermore, the multivariate analysis showed that the Pfizer vaccine had a positive effect on IgG positivity. High antibody IgG titer levels are associated with higher and long-lasting immunity. Taken together, the findings from this study show that the Pfizer BioNTech vaccine may provide better protection against COVID-19 when compared to Sinopharm. the presence of cardiovascular diseases was found to have a significant negative correlation with IgG titers levels after vaccination, thereby suggesting that this patient population may need special attention.

Further studies are required to confirm if booster doses are needed for individuals who have already received Sinopharm and those with specific conditions who did not exhibit IgG titer positivity after vaccination.

Written by

Dr. Maheswari Rajasekaran

Maheswari started her science career with an undergraduate degree in Pharmacy and later went on to complete a master’s degree in Biotechnology in India. She then pursued a Ph.D. at the University of Arkansas for Medical Sciences in the USA.