Three-dose vaccination-induced immune responses protect against SARS-CoV-2 Omicron BA.2: a population-based study in Hong Kong

Background

The ongoing outbreak of SARS-CoV-2 Omicron BA.2 infections in Hong Kong, the model city of universal masking of the world, has resulted in a major public health crisis. Although the third vaccination resulted in strong boosting of neutralization antibody, vaccine efficacy and correlate of immune protection against the major circulating Omicron BA.2 remain to be investigated.

Methods

We investigated the vaccine efficacy against the Omicron BA.2 breakthrough infection among 470 public servants who had received different SARS-CoV-2 vaccine regimens including two-dose BNT162b2 (2 × BNT, n = 169), three-dose BNT162b2 (3 × BNT, n = 168), two-dose CoronaVac (2 × CorV, n = 34), three-dose CoronaVac (3 × CorV, n = 67) and third-dose BNT162b2 following 2 × CorV (2 × CorV+1BNT, n = 32). Humoral and cellular immune responses after three-dose vaccination were further characterized and correlated with clinical characteristics of BA.2 infection.

Findings

During the BA.2 outbreak, 27.7% vaccinees were infected. The timely third-dose vaccination provided significant protection with lower incidence rates of breakthrough infections (2 × BNT 46.2% vs 3 × BNT 13.1%, p < 0.0001; 2 × CorV 44.1% vs 3 × CorV 19.4%, p = 0.003). Investigation of immune responses on blood samples derived from 90 subjects in three-dose vaccination cohorts collected before the BA.2 outbreak revealed that the third-dose vaccination activated spike (S)-specific memory B cells and Omicron cross-reactive T cell responses, which correlated with reduced frequencies of breakthrough infections and disease severity rather than with types of vaccines. Moreover, the frequency of S-specific activated memory B cells was significantly lower in infected vaccinees than uninfected vaccinees before vaccine-breakthrough infection whereas IFN-γ+ CD4 T cells were negatively associated with age and viral clearance time. Critically, BA.2 breakthrough infection boosted cross-reactive memory B cells with enhanced cross-neutralizing antibodies to Omicron sublineages, including BA.2.12.1 and BA.4/5, in all vaccinees tested.

Interpretation

Our results imply that the timely third vaccination and immune responses are likely required for vaccine-mediated protection against Omicron BA.2 pandemic. Although BA.2 conferred the highest neutralization resistance compared with variants of concern tested before the emergence of BA.2.12.1 and BA.4/5, the third dose vaccination-activated S-specific memory B cells and Omicron cross-reactive T cell responses contributed to reduced frequencies of breakthrough infection and disease severity. Neutralizing antibody potency enhanced by BA.2 breakthrough infection in vaccinees with prior 3 doses of CoronaVac or BNT162b2 may reduce the risk of infection against ongoing BA.2.12.1 and BA.4/5.

Funding

Hong Kong Research Grants Council Collaborative Research Fund, Health and Medical Research Fund, Wellcome Trust, Shenzhen Science and Technology Program, the Health@InnoHK, Innovation and Technology Commission of Hong Kong, China, National Program on Key Research Project, Emergency Key Program of Guangzhou Laboratory, donations from the Friends of Hope Education Fund and the Hong Kong Theme-Based Research Scheme.

Effect of silver diamine fluoride and potassium iodide on residual bacteria in dentinal tubules

BACKGROUND

This study evaluated the antimicrobial effect of a silver diamine fluoride (SDF)/potassium iodide (KI) product (Riva Star) on the viability of intratubular bacteria.

METHODS

Forty-five dentine discs prepared from caries-free maxillary premolars were randomly divided into nine groups. Group 1 (negative control) contained non-infected sound dentine discs. The remaining discs were infected with Streptococcus mutans suspension and received dentine treatments as follows: Group 2 (positive control), discs were left untreated; Group 3 SDF/KI (Riva Star); Group 4 chlorhexidine (CHX); Group 5 CHX+SDF/KI; Group 6 Carisolv; Group 7 Carisolv+SDF/KI; Group 8 Papacarie, and Group 9 Papacarie+SDF/KI. The discs were then fractured into two halves, stained with fluorescent LIVE/DEAD stain and observed using confocal laser scanning microscopy.

RESULTS

SDF/KI exhibited a potent antibacterial effect, as represented by a significantly higher percentage of dead bacteria, in comparison with Carisolv and Papacarie (p<0.05). The application of SDF/KI following Carisolv and Papacarie chemomechanical caries removel gels significantly reduced the viability of intra-tubular bacteria in these groups.

CONCLUSIONS

The use of the silver diamine fluoride/potassium iodide product is effective in reducing the numbers of S. mutans in dentinal tubules infected with this organism.

Mechanical disruption of dentin collagen fibrils during resin-dentin bond testing

PURPOSE

To determine if collagen fibrils on the dentin side of failed resin-dentin interfaces undergo mechanical disruption during microtensile bond testing.

MATERIALS AND METHODS

Extracted, caries-free human third molars were divided into four groups. The occlusal enamel was removed, leaving a flat dentin surface for bonding. Resin composite buildups were made after the acid-conditioned dentin was bonded with either Single Bond (S) or One-Step (O), and using either moist bonding (M) or air drying for 5 s (D). After storage in water for 24 h, the teeth were vertically sectioned into an array of 0.9 x 0.9 mm resin composite-dentin beams. They were stressed to failure using the nontrimming version of the microtensile bond test. Fractured dentin and resin composite sides of representative beams from each group that exhibited adhesive failures under light microscopy examination were prepared for scanning (SEM) and transmission electron microscopy (TEM).

RESULTS

A two-way ANOVA showed that moist bond strengths were significantly higher than those made to dry dentin (M > D; p < 0.001), but that there was no difference between the adhesives (S vs O; p = 0.547). SEM analysis showed the presence of loose collagen fibrils within fractured hybrid layers in the dry groups, but not in the moist groups. TEM examination of the dry-bonded groups revealed collagen fibrils that were thinner and exhibited abnormally wide interfibrillar spaces when hybrid layers were intact. Within dry-bonded fractured hybrid layers, broad mechanical disruption zones could be seen, consisting of fibrils that were devoid of cross banding, defibrillation of the subfibrillar architecture, and gross disaggregation into microfibrils. In the moist-bonded groups, only short mechanical disruption zones were found along the torn edges of the collagen fibrils. The rest of the fibrils beyond the fracture site were intact and retained their periodicity. Mechanical testing of demineralized matrices yielded a maximum modulus of elasticity of 43.9 +/- 6.1 MPa.

CONCLUSION

We speculate that adhesive resin has a protective function for demineralized collagen in well-infiltrated hybrid layers. We propose that both the collagen and resin contribute to load sharing during stress application until the final moment of rupture. On the other hand, collagen fibrils in poorly infiltrated hybrid layers, being unsupported by resin, undergo various degrees of irreversible mechanical disruption depending on how the stress is dissipated. The collagen fibril network has a much lower modulus of elasticity compared to those of resin-infiltrated fibrils or the demineralized dentin.

A pilot study of the marginal adaptation and surface morphology of glass-cermet cements

This study investigated changes in the marginal adaptation and surface morphology of Ketac-Silver and Chelon-Silver glass-current cements over time. Dispersalloy amalgam was used as a control. Contralateral pairs of carious primary molars were restored with the test materials and amalgam. Clinical evaluations were scheduled at 12, 18, and 24 months after placement. Gold-plated replicas of the restorations were observed with scanning electron microscopy. Fractures and cracks in the surface of the Dispersalloy and Chelon-Silver increased the surface roughness; however, the damage was superficial and self-limiting in the Dispersalloy restorations, while in Chelon-Silver the fractures caused the material to break down in layers. A substantial quantity of pores, usually smaller than 50 microns in diameter, were observed throughout the surface of the Chelon-Silver restorations. The pores in the surface of Ketac-Silver were fewer and smaller. The incidence of cavomarginal breakdown increased with time. Chelon-Silver restorations had a higher rate of cavomarginal breakdown than did Ketac-Silver and Dispersalloy restorations up to 18 months. However, there was no statistically significant difference in the marginal adaptation of the three groups at 24 months.

Mouthrinses: recent clinical findings and implications for use

Fluoride mouthrinses have been used extensively for the past 15 years to prevent dental caries in children. It has been demonstrated to reduce the incidence of dental caries in children by an average of 30 per cent. For individual patients, dentists should continue to recommend fluoride mouthrinsing at home, based upon the individual's caries activity or risk. This is true whether or not the patient is also receiving the benefits of community water fluoridation. School-based fluoride mouthrinsing programmes are recommended only in fluoride-deficient communities. Its effectiveness will be determined by the caries activity of the participants and the cost to reduce the disease level to an anticipated 30 per cent. Among all the topical fluoride agents, fluoride mouthrinses remain a safe and effective means of controlling dental decay in children and adolescents.

Clinical efficacy of dentifrices in the control of calculus, plaque, and gingivitis

Several dentifrices are available in the market for the control of calculus, plaque, and gingivitis. The anticalculus activity of the pyrophosphate dentifrice formulation has been convincingly demonstrated. Recently, dentifrices containing 0.3% triclosan and 2.0% Gantrez have been shown to possess some anticalculus activity, in addition to their antiplaque and antigingivitis properties. Similarly, sequential application of sanguinarine-containing dentifrice with a brush, followed by a rinse of 30 to 60 seconds, also provides sustained antiplaque and antigingivitis effects. However, other dentifrices have had much less convincing clinical results. It is therefore important for dentists to interpret the therapeutic claims of various antiplaque and antigingivitis dentifrices cautiously before recommending these products to patients.

Evaluation of the use of topical fluoride gel

Professionally applied topical fluoride should be used judiciously and is indicated only in patients with moderate or high caries activity. While the anti-caries effectiveness of acidulated phosphate fluoride gels has been clinically documented, the 2% neutral NaF gel has not been adequately tested, and further clinical verification is needed. Daily use of a self-applied fluoride gel is recommended for patients undergoing orthodontic treatment or to those affected with xerostomia as a result of disease or head and neck radiation therapy. The dental profession and the public should be well informed on the proper use of clinically proven products to achieve optimum effectiveness and minimize the risk of fluoride ingestion.

Effect of protraction headgear on Class III malocclusion

Ten patients with skeletal Class III malocclusion in the early mixed dentition who were treated with maxillary expansion appliance and protraction headgear were compared with reasonably matched controls. Significant orthopedic effects were found after as little as 6 months of treatment. Cephalometric analysis revealed that the correction of Class III malocclusion was primarily a result of forward and downward movement of the maxilla and backward rotation of the mandible. The clinical result of one patient treated with this appliance is used to demonstrate the importance of force magnitudes and directions, as well as the design of the appliance, to the success of the treatment.

Management of rampant caries in children

Because research has resulted in a better understanding of the etiology of dental caries as well as the introduction of new techniques and materials in the practice of dentistry, approaches toward the management of rampant caries should be reevaluated. The development of the acid-etching technique and the improvements in the physical properties and clinical performance of composite resins and glass-ionomer cements have completely changed the concepts of prevention, conservative dentistry, and dental esthetics. Several methods for the treatment of rampant caries are described and management of two cases is documented.