Real-world data on vaccine-elicited neutralising antibody responses for two-dose AZD1222 in African populations are limited. We assessed baseline SARS-CoV-2 seroprevalence and levels of protective neutralizing antibodies prior to vaccination rollout using binding antibodies analysis coupled with pseudotyped virus neutralisation assays in two cohorts from West Africa: Nigerian healthcare workers (n = 140) and a Ghanaian community cohort (n = 527) pre and post vaccination. We found 44 and 28% of pre-vaccination participants showed IgG anti-N positivity, increasing to 59 and 39% respectively with anti-receptor binding domain (RBD) IgG-specific antibodies. Previous IgG anti-N positivity significantly increased post two-dose neutralizing antibody titres in both populations. Serological evidence of breakthrough infection was observed in 8/49 (16%). Neutralising antibodies were observed to wane in both populations, especially in anti-N negative participants with an observed waning rate of 20% highlighting the need for a combination of additional markers to characterise previous infection. We conclude that AZD1222 is immunogenic in two independent West African cohorts with high background seroprevalence and incidence of breakthrough infection in 2021. Waning titres post second dose indicates the need for booster dosing after AZD1222 in the African setting despite hybrid immunity from previous infection.

This work presents prediction and optimisation of controllable parameters of drilling and blasting currently used at the Fobinso Pit of Perseus Mining Ghana Limited (PMGL). The mine faces challenges with blast particle sizes produced after primary blasting. The presence of boulders requires secondary fragmentation to further reduce the broken materials to the acceptable sizes, thereby increasing the cost of production. The mechanical properties of the rocks were determined using Protodyakonov Rock Strength Index. The drill and blast parameters were estimated using the Konya and Walter (1990), Principle of Proportionality, and Instituto Geologo Minero de España (IGME) model developed in 1987. The Modified Kuz-Ram model was used to predict and analyse the results of blasting based on the parameters such as spacing, burden, drillhole diameter, charge density, charge per hole, charge length, and powder factor. A comparative analysis of the predicted size distributions of the various models using diameters of 65 mm and 110 mm revealed no significant differences between the size fractions. The Principle of Proportionality produced the best technical and economic indices for blasting. Keywords: Fragmentation, Drilling Parameters, Primary Blasting, Models, Secondary Blasting

Powder factor can be defined as the quantity of explosives (kg) required to break a unit volume or tonne (t) of rock. The prospect of excavating rocks by blasting is characterized by a specific consumption of explosives. In the past decades, researchers have come up with several precise approaches to predict powder factor or specific charge in blast operations other than through trial blast. Research in this area has focused on the relationship between rock mass properties, blasting material and blasting geometry to establish the powder factor. Also, the interaction between specific energy and particle size embodied in the theory of comminution that is less dependent on local conditions has been studied. In this paper, the various methods for powder factor estimation based on empirical and comminution theory modelling as well as machine learning approaches in both surface bench blasting and underground tunnel operations have been reviewed. The influence of intact rock properties on powder factor selection and the influence of powder factor selection on post-blast conditions have also been discussed. Finally, the common challenges that have been encountered in powder factor estimations have been pointed out in this regard.

There is a paucity of real-world data on vaccine elicited neutralising antibody responses for AZD1222, in African populations following vaccination scale up. Here, we first measured baseline SARS-CoV-2 seroprevalence and levels of protective neutralizing antibodies prior to vaccination rollout using both flow cytometric based analysis of binding antibodies coupled with pseudotyped virus neutralisation assays in two study cohorts from West Africa: Nigerian healthcare workers; (n = 140) and a Ghanaian general community cohort (n = 527). We found that 44% and 28% of pre-vaccination participants showed IgG anti-N positivity, increasing to 59% and 42% respectively with anti-receptor binding dominan (RBD) IgG specific antibodies. The increased prevalence of prior exposure using anti RBD antibodies was corroborated by Pseudotyped virus (PV) neutralizing antibody assays, indicating that overall, 50% of prior infections were missed by N antibody testing. PV titres (serum dilution required to inhibit 50% of infection, ID50) against wild type following 2-dose vaccination regimen were [145 (4.5) to 2579 (4.2) vs 57 (3.0) to 1049 (6.7)] (GMT ± s.d), delta [75 (3.0) to 549 (3.7) vs 37 (2.4) to 453 (7.4)] (GMT ± s.d) and omicron variants [37 (2.4) to 453 (7.4) vs 29 (1.8) to 95 (5.3)] (GMT ± s.d) in the Nigerian (1 month) vs Ghanaian participants (2 months) post vaccination (total n = 94). Previous IgG anti-N was associated with significantly higher neutralizing antibody levels with an observed 3.5-fold [1423 (3.9) vs 4674 (3.4)] (GMT ± s.d) and 2.7-fold [779 (7.1) vs 2128 (4.8) (GMT ± s.d) difference between N positive and negative participants in the Nigerian and Ghanaian cohorts respectively. We also observed serological evidence from N, S and RBD antibodies of breakthrough infection in 8/49 (16%) of Nigerian vaccinees over only 2 months, with neutralisation profiles suggesting delta variant infection consistent with the sampling period when this variant was known to dominate. Importantly, neutralising antibodies waned at 3 months after second dose vs 1 month post second-dose 1695 (4.3)] vs 2579 (4.2) in the Nigerian population who were N negative throughout. IgG anti-N was also observed to wane below cut-off in a total 19/94 (20%) of subjects highlighting the need for a combination of additional markers to characterise previous infection. We conclude that AZD1222 is immunogenic in two independent real world West African cohorts with high background seroprevalence and incidence of breakthrough infection in 2021. Waning titres at 6 months post second dose indicates the need for booster dosing after AZD1222 in the African setting despite hybrid immunity from previous infection.

The West Wall of Nkran Pit Mine is vulnerable to slope instability, mostly due to mining activities.Detailed failure analysis of the discontinuity data of the selected slope was performed using the Dips (6.0) software. The study has shown the likelihood of planar failure, wedge failure, flexural toppling failure and direct toppling failure occurring per the slope angle design of 70°. When the slope angle was increased by 5° and 10°, there were percentage increases in planar, wedge, flexural toppling and direct toppling failure of (1.86 and 7.45)%, (1.23 and 2.81)%, (0.62 and 0.62)% and (0.60 and 1.70)% respectively. It has been recommended that flattening or reducing slope angle could be done as it reduces the weight of material which in turn improves the stability of the slope and also controlled blasting should be employed to minimise excessive damage to the walls.