Comparative Effectiveness of mRNA-1273 and BNT162b2 COVID-19 Vaccines Among Older Adults: Systematic Literature Review and Meta-Analysis Using the GRADE Framework

INTRODUCTION

The mRNA vaccines mRNA-1273 and BNT162b2 demonstrated high efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in phase 3 clinical trials, including among older adults. To inform coronavirus disease 2019 (COVID-19) vaccine selection, this systematic literature review (SLR) and meta-analysis assessed the comparative effectiveness of mRNA-1273 versus BNT162b2 in older adults.

METHODS

We systematically searched for relevant studies reporting COVID-19 outcomes with mRNA vaccines in older adults aged ≥ 50 years by first cross-checking relevant published SLRs. Based on the cutoff date from a previous similar SLR, we then searched the WHO COVID-19 Research Database for relevant articles published between April 9, 2022, and June 2, 2023. Outcomes of interest were SARS-CoV-2 infection, symptomatic SARS-CoV-2 infection, severe SARS-CoV-2 infection, COVID-19-related hospitalization, and COVID-19-related death following ≥ 2 vaccine doses. Random effects meta-analysis models were used to pool risk ratios (RRs) across studies. Heterogeneity was evaluated using chi-square testing. Evidence certainty was assessed per GRADE framework.

RESULTS

Twenty-four non-randomized real-world studies reporting clinical outcomes with mRNA vaccines in individuals aged ≥ 50 years were included in the meta-analysis. Vaccination with mRNA-1273 was associated with significantly lower risk of SARS-CoV-2 infection (RR 0.72 [95% confidence interval (CI) 0.64‒0.80]), symptomatic SARS-CoV-2 infection (RR 0.72 [95% CI 0.62‒0.83]), severe SARS-CoV-2 infection (RR 0.67 [95% CI 0.57‒0.78]), and COVID-19-related hospitalization (RR 0.65 [95% CI 0.53‒0.79]) but not COVID-19-related death (RR 0.80 [95% CI 0.64‒1.00]) compared with BNT162b2. There was considerable heterogeneity between studies for all outcomes (I2 > 75%) except death (I2 = 0%). Multiple subgroup and sensitivity analyses excluding specific studies generally demonstrated consistent results. Certainty of evidence across outcomes was rated as low (type 3) or very low (type 4), reflecting the lack of randomized controlled trial data.

CONCLUSION

Meta-analysis of 24 observational studies demonstrated significantly lower risk of asymptomatic, symptomatic, and severe infections and hospitalizations with the mRNA-1273 versus BNT162b2 vaccine in older adults aged ≥ 50 years.

Comparative effectiveness of mRNA-1273 and BNT162b2 COVID-19 vaccines in immunocompromised individuals: a systematic review and meta-analysis using the GRADE framework

Introduction

Despite representing only 3% of the US population, immunocompromised (IC) individuals account for nearly half of the COVID-19 breakthrough hospitalizations. IC individuals generate a lower immune response after vaccination in general, and the US CDC recommended a third dose of either mRNA-1273 or BNT162b2 COVID-19 vaccines as part of their primary series. Influenza vaccine trials have shown that increasing dosage could improve effectiveness in IC populations. The objective of this systematic literature review and pairwise meta-analysis was to evaluate the clinical effectiveness of mRNA-1273 (50 or 100 mcg/dose) vs BNT162b2 (30 mcg/dose) in IC populations using the GRADE framework.

Methods

The systematic literature search was conducted in the World Health Organization COVID-19 Research Database. Studies were included in the pairwise meta-analysis if they reported comparisons of mRNA-1273 and BNT162b2 in IC individuals ≥18 years of age; outcomes of interest were symptomatic, laboratory-confirmed SARS-CoV-2 infection, SARS-CoV-2 infection, severe SARS-CoV-2 infection, hospitalization due to COVID-19, and mortality due to COVID-19. Risk ratios (RR) were pooled across studies using random-effects meta-analysis models. Outcomes were also analyzed in subgroups of patients with cancer, autoimmune disease, and solid organ transplant. Risk of bias was assessed using the Newcastle-Ottawa Scale for observational studies. Evidence was evaluated using the GRADE framework.

Results

Overall, 17 studies were included in the pairwise meta-analysis. Compared with BNT162b2, mRNA-1273 was associated with significantly reduced risk of SARS-CoV-2 infection (RR, 0.85 [95% CI, 0.75-0.97]; P=0.0151; I2 = 67.7%), severe SARS-CoV-2 infection (RR, 0.85 [95% CI, 0.77-0.93]; P=0.0009; I2 = 0%), COVID-19-associated hospitalization (RR, 0.88 [95% CI, 0.79-0.97]; P<0.0001; I2 = 0%), and COVID-19-associated mortality (RR, 0.63 [95% CI, 0.44-0.90]; P=0.0119; I2 = 0%) in IC populations. Results were consistent across subgroups. Because of sample size limitations, relative effectiveness of COVID-19 mRNA vaccines in IC populations cannot be studied in randomized trials. Based on nonrandomized studies, evidence certainty among comparisons was type 3 (low) and 4 (very low), reflecting potential biases in observational studies.

Conclusion

This GRADE meta-analysis based on a large number of consistent observational studies showed that the mRNA-1273 COVID-19 vaccine is associated with improved clinical effectiveness in IC populations compared with BNT162b2.

The Use of Salmonella Typhim Vaccine to Diagnose Antibody Deficiency

PURPOSE

The specific antibody response to the unconjugated 23-valent pneumococcal polysaccharide vaccine is one of the most common tests used to assess for possible humoral immunodeficiency. The results can be difficult to interpret because most people have been immunized with one or more of the pneumococcal vaccines and there is controversy regarding what constitutes a normal response. To circumvent this problem, we developed an ELISA to measure IgG-specific antibodies to the Salmonella Vi Typhim (S. Typhim) vaccine, a pure polysaccharide vaccine, which is a neoantigen for the vast majority of people in the USA.

METHODS

We compared the pre- and post-vaccination serum titers to the Vi Typhim vaccine in healthy controls (n = 22), patients previously diagnosed with a primary immunodeficiency (n = 30), and patients referred for possible humoral immune deficiency (n = 29). We also determined if the S. Typhim vaccine could be used to assess specific antibody responses in people on antibody replacement therapy.

RESULTS

Following immunization with the S. Typhim vaccine, we found that a 2-fold increase in titers is 100% sensitive and specific in detecting known humoral immune deficiencies as determined by ROC curve analysis. This cut-off value was successfully applied to possible immune deficiency patients (n = 29), resulting in the diagnosis of seven subjects with humoral immunodeficiency. The use of immunoglobulin replacement therapy did not affect the median response ratios compared to subjects not receiving gammaglobulin.

CONCLUSION

This study suggests that measurement of the specific antibody response to the S. Typhim vaccine may have advantages over pneumococcal vaccination in the evaluation of the humoral immune response.

Cloning, sequence and characterization of the human AMPD2 gene: evidence for transcriptional regulation by two closely spaced promoters

AMP deaminase (AMPD) is manifest through a multigene family in higher eukaryotes, including man. The human AMPD1 and AMPD3 genes have been cloned and partially characterized. This study describes the cloning, chromosomal localization, partial sequence and characterization of the human AMPD2 gene. Composed of nineteen exons and eighteen intervening sequences spanning nearly 14 kb of genomic DNA, the human AMPD2 gene is positioned on the short arm of chromosome 1 near the p13.3 boundary. Two alternative 5' exons (1A and 1B) are remotely located upstream, whereas the other seventeen are compressed into the 3' terminal one-half of the gene. Transient transfections of human retinal pigment epithelial (RPE) cells using heterologous constructs containing 5' flanking and 5' untranslated sequences cloned upstream of a luciferase reporter gene show that promoter activities are associated with exons 1A and 1B. Inspection of genomic DNA sequence reveals that AMPD2 promoter regions lack readily identifiable TATA boxes and are G + C-rich, particularly in the region of multiple transcription initiation sites in exon 1A. The regulation and evolution of the entire human AMPD multigene family are discussed.

Divergent N-terminal regions in AMP deaminase and isoform-specific catalytic properties of the enzyme

AMP deaminase (AMPD) catalyzes the hydrolytic deamination of AMP to IMP and NH3. This activity is represented throughout mammalian tissues and cells by at least three isoforms. Human AMPD cDNAs have been cloned and sequenced, leading to predictions that each isoform contains distinct amino-ends (N-terminal regions) in contrast to their highly conserved carboxyl-ends (C-terminal regions). Wild type, truncated, and chimeric human AMPD1 (isoform M) and AMPD2 (isoform L) cDNAs were expressed and the resultant activities partially characterized as a means to examine the role of divergent N-terminal regions in these polypeptides (residues 1-262 and 1-258 of isoforms M and L, respectively) on isoform-specific catalytic properties. Similar to activities purified from human tissues, in the presence of monovalent cation, wild type isoform M displayed hyperbolic kinetics in the presence and absence of ATP, whereas wild type isoform L exhibited allosteric activation in the presence of this nucleotide effector. Expression of both a chimeric M (5'-AMPD1)/L (3'-AMPD2) construct and one in which the N-terminal region of isoform L was deleted produced activities that were also allosterically regulated by ATP. However, no AMPD activity was detectable following expression of either a chimeric L (5'-AMPD2)/M (3'-AMPD1) construct or one in which the N-terminal region of isoform M had been deleted. The N-terminal region also affected the relative ability of each recombinant AMPD activity to deaminate substrate analogs modified in either the sugar or the phosphate, but not in the purine base, moieties of AMP. These combined data show (i) that isoform M, but not isoform L, absolutely requires its N-terminal region for proper function, (ii) that the C-terminal region of isoform L is responsible for allosteric activation by ATP, (iii) an effect of the N-terminal region on substrate-enzyme interaction, a contention that is discussed in context with available information regarding the related purine catabolic activity, adenosine deaminase.

Molecular cloning of AMP deaminase isoform L. Sequence and bacterial expression of human AMPD2 cDNA

Human AMPD2 cDNA clones have been isolated from T-lymphoblast and placental lambda gt11 libraries utilizing a previously cloned rat partial AMPD2 cDNA as the probe. Alignment analysis of all cDNA clones indicates the presence of intervening sequences in several placental isolates. This has been confirmed by sequencing human AMPD2 genomic clones. Intervening sequences can be removed from the cDNA clones by restriction with endonucleases at unique sites within the proposed open reading frame. This results in a 3292-base pair cDNA proposed to contain the entire AMPD2 open reading frame, which would encode a 760-amino acid polypeptide with a predicted subunit molecular mass of 88.1 kDa. Nucleotide and predicted amino acid comparisons with the 264 base pairs of proposed coding sequences in the rat AMPD2 cDNA demonstrate 91% similarity and identity, respectively. A comparison of the predicted human AMPD1 and AMPD2 polypeptides demonstrates homology in their C-terminal domains. Included in this region is the conserved motif, SLSTDDP, proposed to be part of the catalytic site of all AMP deaminases. In contrast, the predicted N-terminal domains of the human AMPD1 and AMPD2 polypeptides are unique. When placed in a prokaryotic expression vector, the human AMPD2 cDNA expresses AMP deaminase activity which can be precipitated with polyclonal antisera specific for isoform L.