Geometric Mean Index Research Articles

Optimising Stock Market Indices for Emerging Economies: An Empirical Study of the Iraqi Stock Exchange

This research explores the efficiency of different ways to construct a stock market index in the Iraqi Stock Exchange (ISX) context, an emerging market with unique traits. Five methods are considered: Price-Weighted Index (PWI), Equal-Weighted Index (EWI), Geometric Mean Index (GMI), Risk-Weighted Index (RWI) and Volatility-Weighted Index (VWI). The ISX60 index is used as a benchmark against their performance. The study employs 57 stocks listed on the ISX from August 2022 to August 2024, covering two years. We examine each method’s stability, performance, and representativeness through graphical analysis and comparative evaluation when building an index. The results indicate that broader indices with more components show higher stability under all constructions. GMI works well in tracking general trends across the market, while RWI and VWI appear effective at controlling risk and reducing exposure to volatile assets, respectively. It also underscores diversification as critical for constructing indices and tradeoffs between representation versus stability in emerging markets. Such insights enhance understanding of how indices can be created in developing financial systems and have practical implications for investors, policymakers, and financial analysts operating within Iraqi or similar emerging economy settings.

Influences of lithium on soil properties and enzyme activities

Lithium is an emerging environmental contaminant under the current sustainable energy strategy, but little is known about its contamination characteristic in soil. In this study, soil properties and enzyme activities in soils treated with 10–1280 mg kg−1 lithium were measured. The results showed that the content of ammonium nitrogen, total nitrogen, and exchangeable potassium significantly increased by 64.39%–217.73%, 23.06%–131.86%, and 4.76%–16.10%, while electric conductivity and available phosphorus content in lithium treated soils was respectively as 1.10-fold–13.44-fold and 1.27-fold–6.66-fold comparing to CK value. Soil pH and cation exchange capacity slightly declined and increased, respectively, and there was no significant variation in total organic carbon. However, nitrate nitrogen and sulfate content significantly decreased under higher lithium stress. On the other hand, lower lithium treatment level of 10, 20, 40, or 80 mg kg−1 selectively promoted the activities of sucrase, urease, aryl sulfatase, and peroxidase, while the protease, neutral phosphatase, phytase, and lipase were significantly inhibited under all lithium levels, indicating a weaken geochemical cycling of carbon, nitrogen, phosphorus, and sulfur. Then, lithium's 10% and 50% ecological dose (ED10 and ED50) was respectively fitted as 21.18 and 1408.67 mg kg−1 basing on Geometric Mean Index. The influences of lithium on soil were adverse. This study provided important insights into understanding the characteristics of lithium contamination, informing risk assessment and guiding remediation.

Stringency of containment and closures on the growth of SARS-CoV-2 in Canada prior to accelerated vaccine roll-out

BackgroundMany studies have examined the effectiveness of non-pharmaceutical interventions (NPIs) on SARS-CoV-2 transmission worldwide. However, less attention has been devoted to understanding the limits of NPIs across the course of the pandemic and along a continuum of their stringency. In this study, we explore the relationship between the growth of SARS-CoV-2 cases and an NPI stringency index across Canada before the accelerated vaccine roll-out. MethodsWe conducted an ecological time-series study of daily SARS-CoV-2 case growth in Canada from February 2020 to February 2021. Our outcome was a back-projected version of the daily growth ratio in a stringency period (i.e., a 10-point range of the stringency index) relative to the last day of the previous period. We examined the trends in case growth using a linear mixed-effects model accounting for stringency period, province, and mobility in public domains. ResultsCase growth declined rapidly by 20–60% and plateaued within the first month of the first wave, irrespective of the starting values of the stringency index. When stringency periods increased, changes in case growth were not immediate and were faster in the first wave than in the second. In the first wave, the largest decreasing trends from our mixed effects model occurred in both early and late stringency periods, depending on the province, at a geometric mean index value of 30⋅1 out of 100. When compared with the first wave, the stringency periods in the second wave possessed little association with case growth. ConclusionsThe minimal association in the first wave, and the lack thereof in the second, is compatible with the hypothesis that NPIs do not, per se, lead to a decline in case growth. Instead, the correlations we observed might be better explained by a combination of underlying behaviors of the populations in each province and the natural dynamics of SARS-CoV-2. Although there exist alternative explanations for the equivocal relationship between NPIs and case growth, the onus of providing evidence shifts to demonstrating how NPIs can consistently have flat association, despite incrementally high stringency.

Ecotoxicological impact of the antihypertensive valsartan on earthworms, extracellular enzymes and soil bacterial communities.

The use of reclaimed water in agriculture represents a promising alternative to relieve pressure on freshwater supplies, especially in arid or semiarid regions facing water scarcity. However, this implies introducing micropollutants such as pharmaceutical residues into the environment. The fate and the ecotoxicological impact of valsartan, an antihypertensive drug frequently detected in wastewater effluents, were evaluated in soil-earthworm microcosms. Valsartan dissipation in the soil was concomitant with valsartan acid formation. Although both valsartan and valsartan acid accumulated in earthworms, no effect was observed on biomarkers of exposure (acetylcholinesterase, glutathione S-transferase and carboxylesterase activities). The geometric mean index of soil enzyme activity increased in the soils containing earthworms, regardless of the presence of valsartan. Therefore, earthworms increased soil carboxylesterase, dehydrogenase, alkaline phosphatase, β-glucosidase, urease and protease activities. Although bacterial richness significantly decreased following valsartan exposure, this trend was enhanced in the presence of earthworms with a significant impact on both alpha and beta microbial diversity. The operational taxonomic units involved in these changes were related to four (Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes) of the eight most abundant phyla. Their relative abundances significantly increased in the valsartan-treated soils containing earthworms, suggesting the presence of potential valsartan degraders. The ecotoxicological effect of valsartan on microbes was strongly altered in the earthworm-added soils, hence the importance of considering synergistic effects of different soil organisms in the environmental risk assessment of pharmaceutical active compounds.

Ecological improvement of antimony and cadmium contaminated soil by earthworm Eisenia fetida: Soil enzyme and microorganism diversity

Vermiremediation on improvement of antimony (Sb) and cadmium (Cd) contaminated soil was less reported. In this study, earthworm Eisenia fetida was exposed into soil spiked with Sb and Cd and their mixture for 30 days, and then we measured multiple soil enzyme activities and bacteria communities via enzymatic reaction and high-throughput sequencing of 16 S rRNA genes. The results showed that Sb and Cd at high treatment levels inhibited the activities of urease, neutral phosphatase and protease significantly, but earthworm could promote the activities of urease and neutral phosphatase by 17.75%–121.91% and 1.46%–118.97%, respectively. However, earthworms inhibited catalase and had no effect on protease. The Geometric Mean Index suggested that earthworms led to a higher soil biochemistry function. According to a taxonomic analysis, bacterial community structure predominantly consisted of phylum Proteobacteria, Actinobacteria, Firmicutes, etc. and class Gammaproteobacteria, Actinobacteria, Alphaproteobacteria, etc.; furthermore, Pielou index and Shannon index (Alpha diversity in the habitat) indicated that bacteria diversity and evenness increased in the presence of earthworms. The heating map revealed that earthworms made genus Sphingomonas, Flavobacterium, etc. and species Sphingomonas jaspsi, Conexibacter, etc. dominate. Overall, earthworm is a suitable remediation species to improve the ecological function of heavy metal polluted soil. However, the specific mechanism and causal relationship of how earthworm to control enzyme activity and bacteria community remained to be explored.

Weighted geometric mean index: A model to evaluate drought tolerance in post-rainy season sorghum (Sorghum bicolor (L.) Moench)

In India, post-rainy season sorghum, a cereal crop is very crucial for food and fodder security in the drought prone areas. The aim of this study was to provide an improved or better index to identify drought-tolerant genotypes. Stress susceptible index (SSI) is currently the most commonly used index by plant breeders globally to select drought-tolerant genotypes. However, SSI has certain limitations which can be addressed by new index, i.e., weighted geometric mean index (WGMI). In the present study, 42 and 25 genotypes were evaluated under three environments during the post-rainy seasons of 2015–2016 and 2016–2017, respectively, using split plot design. Genotypes were categorized as tolerant, moderately tolerant and susceptible using model WGMI. Significant and negative correlations were observed between WGMI and SSI for grain and stover yield in most of the cases. The best index to identify drought-tolerant genotypes must be highly significantly correlated with traits under stress and non-stress environments. In this context, our proposed index demonstrated higher correlation with grain and stover yield in comparison with SSI and higher coefficient of determination to identify drought-tolerant genotypes. WGMI was found to be more appropriate and reliable indicator, as it gives information regarding higher yield along with drought tolerance. In addition, it was shown to provide information on wide adaptability of genotypes under several environments. The correlation studies suggested that the traits associated with drought tolerance were early flowering, longer peduncle length and higher panicle emergence (percent).

Nutrient cycling and soil-related processes under different land covers of semi-arid rangeland ecosystems in northern Iran

There are contrasting reports about whether and how land covers influence soil organic matter fractions and microbial activities. To the best of the authors’ knowledge, the relationship between above-ground plant cover and the nutrient cycling in semi-arid areas, which are often considered as especially fragile and sensitive ecosystems, are almost unknown. The purpose of this research was to evaluate the influence of different shrub and grasslands located in northern Iran on the fractions of soil particulate and dissolved organic matter, microbial/enzyme activities. In this study, a total of 15 soil samples (30 × 30 × 10 cm) from each vegetation type [i.e. (1) Crataegus microphylla C. Koch., (2) Berberis integerrima Bunge., (3) Ribes Uva – crispa L., (4) Prunus spinosa L., (5) rangeland cover with dominant Lecokia cretica (Lam.) DC., Orchis mascula L., Cardamine bulbifera (L.) Crantz, and (6) rangeland cover with the dominance of Fragaria vesca L.] were transferred to the laboratory. Berberis significantly increased soil particulate organic C (2.26 g kg−1), but the maximum particulate organic N (0.27 g kg−1) was found under the Cratagus plant type. Soil dissolved organic C content was found to be significantly higher under Berberis (38.08 mg kg−1) ≈ Cratagus (34.81 mg kg−1), whereas the soil dissolved organic N was enhanced in Cratagus (22.84 mg kg−1) land cover. Significantly higher values of basal and substrate induced respiration (0.27 and 1.22 mg CO2 g−1 day−1, respectively) were found under Berberis when compared with the other land covers. Soil microbial biomass C and P were found to be significantly higher under Cratagus (259.90 and 61.00 mg kg−1) and Berberis (273.72 and 54.80 mg kg−1), whereas microbial biomass of N was enhanced under Cratagus (36.88 mg kg−1) plant type. Soil urease (18.22 µg NH4+–N g−1 2 h−1), acid phosphatase (305.66 µg PNP g−1 h−1), arylsulfatase (90.60 µg PNP g−1 h−1), invertase (97.53 µg Glucose g−1 3 h−1), geometric mean (4.73) and Shannon's diversity index (0.15) of enzyme activities were significantly increased in the topsoil of Cratagus compared with the other vegetation types. Based on principal component analysis (PCA), Cratagus, Berberis, and Ribes enhanced soil organic matter fractions, microbial and enzyme activities and were related to higher amounts of soil moisture, pH, organic C, total N, available P, fulvic/humic acids, and root biomass. Pasture and Prunus decreased the fractions of organic matter and soil microbial activities and most often affected the stoichiometry of carbon sources. It was concluded that shrubs (especially Cratagus and Berberis) can play a crucial role in nutrient cycling and soil-related processes in semi-arid rangeland ecosystems.

Distribution of soil nutrients and enzyme activities in different aggregates under two sieving methods

AbstractSoil aggregates are the basic units of soil structure. Dry and wet sieving are two conventional methods used for isolating aggregates. However, different methods can cause variation in the distribution of enzymes and nutrients. For better understanding the influence of water on soil aggregate stability and building the relationship between soil nutrients and the enzyme activity of aggregates, three soil samples with different organic matter (OM) content were selected: Qiyang, Hunan (HN); Hailun, Heilongjiang (HLJ); and Changshu, Jiangsu (JS). In this study, we measured the enzyme activity of invertase (INV), urease (URE), phosphatase (PHO), and arylsulfatase (ARY) together the OM, total N (TN), available N (AN), available P, and available K of dry and wet sieved aggregates. The results showed that wet sieving caused 34.0, 66.8, and 35.1% decreases in the soil mean weight diameter for HN, HLJ, and JS, respectively. The TN content of wet sieved aggregates decreased to various degrees (19.9–47.7%) compared with dry sieving. The activity of INV, PHO, and ARY decreased sharply after wet sieving especially for microaggregates (reached 70% in <0.1‐mm particles of JS). Enzyme activities were mainly located in microaggregates under dry isolation but changed to macroaggregates after wet sieving. The geometric mean (GMean) index of <0.1‐mm particles were 1.54, 1.01 and 1.36 times higher than that of >2‐mm aggregates under dry sieving. Furthermore, the GMean index showed a significant positive relationship with soil OM, TN, and AN under both dry and wet sieving methods.

Sustainable development and environmental security in the countries of the circumpolar north

The article presents a comparative analysis of the sustainable development of eight circumpolar countries: Norway, Sweden, Finland, Russia, the USA, Canada, Denmark, and Iceland. Sustainability is understood as the interdependent development of five spheres of human activity: economic, industrial, social, demographic, innovative-technological, and ecological. Each sphere is assessed in terms of endogenous variables that are influenced by exogenous factors. The demographic sphere is evaluated by population; the social – by the human development index (HDI); economic-industrial – GDP per capita (PPP); environmental – extent of exposure of the population to particulate matter in the atmosphere having a diameter of 2.5 μm; innovative-technological – by high-tech exports. The novelty lies in the analysis of the sustainable development of the respective countries using ADL-modelling. Five interdependent econometric equations are presented along with a method for calculating coefficients. The concept of economic, social and environmental sustainability coefficients is introduced. Each country’s sustainability index was calculated as the geometric mean index of economic, social and environmental sustainability. The results of a comparison of the circumpolar countries according to the sustainable development index are presented. The model can predict the development of each sphere of the respective country’s life-sustaining functions and determine the predicted values of the country’s sustainable development index, as well as to compare the development of countries on sustainable development and environmental safety.

Hospital length of stay following admission for traumatic brain injury in a Canadian integrated trauma system: A retrospective multicenter cohort study

BackgroundTraumatic brain injury (TBI) is the leading cause of disability in children and young adults and costs CAD$3 billion annually in Canada. Stakeholders have expressed the urgent need to obtain information on resource use for TBI to improve the quality and efficiency of acute care in this patient population. We aimed to assess the components and determinants of hospital and ICU LOS for TBI admissions. MethodsWe performed a retrospective multicenter cohort study on 11,199 adults admitted for TBI between 2007 and 2012 in an inclusive Canadian trauma system. Our primary outcome measure was index hospital LOS (admission to the hospital with the highest designation level). Index LOS was compared to total LOS (all consecutive admissions related to the injury). Expected LOS was calculated by matching TBI admissions to all-diagnosis hospital admissions by age, gender, and year of admission. LOS determinants were identified using multilevel linear regression. ResultsGeometric mean total LOS was 1day longer than geometric mean index LOS (12.6 versus 11.7 days). Observed index and ICU LOS were respectively 4.2days and 2.5days longer than that expected according to all-diagnosis admissions. The six most important determinants of LOS were discharge destination, severity of concomitant injuries, extracranial complications, GCS, TBI severity, and mechanical ventilation, accounting for 80% of explained variation. ConclusionsResults of this multicenter retrospective cohort study suggest that hospital and ICU LOS for TBI admissions are 56% and 119% longer than expected according to all-diagnosis admissions, respectively. In addition, hospital LOS is underestimated when only the index visit is considered and is largely influenced by discharge destination and extracranial complications, suggesting that improvements could be achieved with better discharge planning and interventions targeting prevention of in-hospital complications. This study highlights the importance of considering TBI patients as a distinct population when allocating resources or planning quality improvement interventions.

Geometric mean quantity index numbers with Benefit-of-the-Doubt weights

Geometric mean index numbers are a multiplicative aggregation of (price or quantity) ratios with their importance exponents/weights derived from one or more observed budget shares. In the specific context of composite indicator construction, we propose to use the budget shares as naturally generated by the linear Benefit-of-the-Doubt model. This approach is directly inspired by the literature on index number theory. Our basic model is easily extended to provide transitive composite indicator orderings in a multilateral setting. Also, a multi-factor decomposition is proposed to explain the intertemporal evolution of a single entity. We illustrate our results with social inclusion data for the EU-countries.

Selection indices to identify maize (Zea mays L.) hybrids adapted under drought-stress and drought-free conditions in a tropical climate

Drought stress is the most important production constraint in maize (Zea mays L.), especially in rainfed agriculture. To improve productivity of rainfed maize, the development of hybrids with tolerance to drought stress is an important objective in maize breeding programs. The present study was undertaken to identify maize hybrids that perform better under drought-stress and drought-free conditions by using various selection indices. These selection indices were calculated on the basis of yield (t ha–1) performance of hybrids measured under drought stress and optimum environments. A set of 38 cultivars was evaluated at 10 environments (representing five each of drought stress and optimum growing conditions). The average reduction in grain yield due to drought stress was 52%. Effects of genotype, environment and their interaction were significant sources of variation in determining grain yield, respectively explaining 5.0–7.4%, 55.0–60.2% and 12.0–15.0% of total variation in yield under drought-stress and drought-free conditions. Of eight selection indices considered for study, three indices such as harmonic mean, geometric mean, and stress tolerance index were identified as suitable for selection of genotypes capable of performing well both under drought-stress and drought-free environments. Drought response index and drought resistance index were found useful in identifying hybrids that performed better under drought stress. Stress susceptibility index was negatively correlated with yield measured under drought stress. Stress susceptibility index could be used as selection index but only in combination with yield performance data under water-deficit conditions in order to identify drought-tolerant hybrids with reasonable productivity. Test weight, shelling percentage, days to maturity, and ear girth were found to be useful traits for improving yield performance across diverse environments. Cultivation of identified drought-tolerant hybrids would be useful to enhance maize productivity in drought-stress environments.

Linking indices for biodiversity monitoring to extinction risk theory.

Biodiversity indices often combine data from different species when used in monitoring programs. Heuristic properties can suggest preferred indices, but we lack objective ways to discriminate between indices with similar heuristics. Biodiversity indices can be evaluated by determining how well they reflect management objectives that a monitoring program aims to support. For example, the Convention on Biological Diversity requires reporting about extinction rates, so simple indices that reflect extinction risk would be valuable. We developed 3 biodiversity indices that are based on simple models of population viability that relate extinction risk to abundance. We based the first index on the geometric mean abundance of species and the second on a more general power mean. In a third index, we integrated the geometric mean abundance and trend. These indices require the same data as previous indices, but they also relate directly to extinction risk. Field data for butterflies and woodland plants and experimental studies of protozoan communities show that the indices correlate with local extinction rates. Applying the index based on the geometric mean to global data on changes in avian abundance suggested that the average extinction probability of birds has increased approximately 1% from 1970 to 2009.Conectando Índices para el Monitoreo de la Biodiversidad con la Teoría de Riesgo de ExtinciónResumenLos índices de biodiversidad combinan frecuentemente los datos de diferentes especies cuando se usan en los programas de monitoreo. Las propiedades heurísticas pueden sugerir índices preferidos, pero carecemos de medios objetivos para discriminar a los índices con propiedades heurísticas similares. Los índices de biodiversidad pueden evaluarse al determinar qué tan bien reflejan los objetivos de manejo que un programa de monitoreo busca apoyar. Por ejemplo, la Convención sobre la Diversidad Biológica requiere reportar las tasas de extinción, así que los índices que reflejan el riesgo de extinción serían valiosos. Desarrollamos 3 índices de biodiversidad que se basan en modelos sencillos de viabilidad de población y que relacionan el riesgo de extinción con la abundancia. Basamos el primer índice en la media geométrica de la abundancia de especies, y el segundo en una media de poder más general. En el tercer índice integramos la media geométrica y la tendencia. Estos índices requieren los mismos datos que índices previos, pero también se relacionan directamente con el riesgo de extinción. La información de campo sobre mariposas y plantas de bosque, y los estudios experimentales de comunidades protozoarias, muestran que los índices se correlacionan con las tasas locales de extinción. Al aplicar el índice basado en la media geométrica sobre los datos globales de los cambios en la abundancia de aves, sugirió que la probabilidad de extinción promedio de aves ha incrementado aproximadamente 1% desde 1970 hasta 2009.Palabras ClaveÍndice de biodiversidad, media geométrica, medida de la biodiversidad, riesgo de extinción

Fine‐tuning the assessment of large‐scale temporal trends in biodiversity using the example ofBritish breeding birds

Bird populations are seen as useful indicators of the health of wildlife and the countryside because they occupy a range of habitats, they tend to be towards the top of the food chain, and data is provided by long‐term surveys. Hence, many countries apply wild bird indicators (WBIs), quantifying trends in biodiversity, to monitor environmental health. TheUK'sWBI, for example, has become one of the government's headline indicators of sustainable development. Understanding the population changes underlying the estimated trends is indispensable if we are to allocate limited resources more effectively. Employing a novel set of measures alongside the traditional geometric mean index, we analyse diversity trends amongBritish breeding birds. It reveals that species that are scarce, but not yet in the focus of conservation action, may be the ‘losers’ in biodiversity action plans. This suggests that additional resources should be devoted to species showing long‐term decline before they reach the low population levels that currently trigger large‐scale species‐specific rescue projects.

A rent index for the private rental sector in Flanders

This paper describes the construction of a rent index for Flanders, Belgium. This annual index, referred to as the huurprijsindex (rent index), is designed to detect changes in rents for the overall stock of rental homes. We use the matched model methodology based upon repeat tenancy agreements, analogous to Case and Shiller’s geometric repeat sales model, to estimate the rent index. We use recoded data on the tenancy agreements of nearly five hundred thousand rental homes; more than 30,000 of these represent repeat agreements between 1990 and 2010. The accuracy of the index is determined using the 95 % confidence interval. Given our target (a geometric mean index value) and the characteristics of the dataset (large but without property characteristics) our repeat tenancy agreements method seems to be adequate for calculating a rent index for Flanders.

Developing a House Price Index for The Netherlands: A Practical Application of Weighted Repeat Sales

This paper describes the development of a house price index that has been introduced in May 2005 in The Netherlands. This monthly index, called Woningwaarde Index Kadaster (House Price Index Kadaster), is designed to detect changes in the price of the overall stock of owner-occupied homes. Fifty-five indices are calculated: one overall index, four regional indices, 12 provincial indices and 38 indices based on combinations of region/province and dwelling type. We used Case and Shiller’s geometric Weighted Repeat Sales Model to calculate monthly house price indices. We used recorded data on the sales of over 500,000 owner-occupied homes in The Netherlands, all representing repeat sales between January 1993 and December 2006. The accuracy of the index was determined using the 95% confidence interval. We observed that accuracy might become a problem in smaller sub samples. Revision volatility was explored by comparing the index values computed from all available data until December 2005 with the index values computed from the data available until December 2006. Our analysis showed that revision volatility does not seem to be a major problem to the index. We also explored heteroskedasticity in the Repeat Sales method but did not find conclusive evidence for the proposed heteroskedasticity. Given our target (a geometric mean index value) and the characteristics of the dataset (very large but without property characteristics) the Repeat Sales Method seems to be adequate for calculating a house price index for The Netherlands.

Direct and indirect time dummy approaches to hedonic price measurement

Quality-adjusted price indexes are frequently obtained by estimating how much of the price difference between a disappearing item and its replacement is due to a quality difference. Hedonic regression has become a popular quality-adjustment method among statistical agencies. The use of the time dummy method is still very limited, though. This paper has two aims. First, it shows how this method fits into the matched-model methodology of agencies applying a geometric mean index formula at the elementary aggregation level. Second, the paper argues that the ordinary or 'direct' time dummy approach cannot cope with systematic price effects of new and disappearing products. Several 'indirect' alternatives are discussed in which the time dummy coefficient serves as a common adjustment factor and in which systematic effects of unmatched products are explicitly taken into account. Special attention is paid to the role of the sampling design, in particular to product sampling proportional to expenditure.

Additive decompositions for Fisher, Törnqvist and geometric mean indexes

Users of a price or quantity index often want to know how much each item in the index contributes to its overall change. Consequently, statistical agencies generally publish items’ contributions to changes in the indexes that they publish. For fixed basket index formulas, calculating contributions to index change that add up to the correct total is straightforward, but for Fisher, Tornqvist and geometric mean index formulas – which statistical agencies are beginning to use – it is not. We use economic and axiomatic approaches to derive additive decompositions of the change in a Fisher index, and we use an axiomatic approach to derive an additive decomposition of the change in a Tornqvist or geometric mean index.

Pertussis antibody levels in infants immunized with an acellular pertussis component vaccine, measured using whole-cell pertussis ELISA.

A commercially available whole-cell pertussis IgG ELISA was used to test the response of 137 2-month-old infants to immunization with a trivalent acellular pertussis vaccine. The pre-immunization geometric mean (GM) IgG index was 6.96 (95% confidence interval (CI) 5.88-8.04) and the postimmunization GM index was 13.16 (95% CI 12. 20-14.11), P < 0.001. Eighty percent of subjects (110/137) had a significant 1.5-fold increase of pertussis IgG index (97/137, 71%) or a postimmunization IgG index > 10 (93/137, 68%). In single antigen ELISA, 83% showed at least a fourfold increase in pertussis toxin-specific IgG (PT-IgG) and 91% showed an increase in IgG specific for filamentous haemagglutinin (FHA-IgG). Four percent had high pre- immunization antibody levels (index > 20), likely to reflect recent maternal exposure to pertussis. This correlated with a smaller increase in pertussis IgG index. A decline in pertussis IgG index postimmunization occurred in 17/24 infants (71%) whose pre-immunization IgG index was > 10. This postimmunization pertussis IgG index was not significantly different to that of infants with a low pre-immunization index. A similar trend was noted with PT-IgG and FHA-IgG results. The whole-cell ELISA can detect a response to acellular pertussis vaccination in most infants if both antibody index and degree of seroconversion are calculated and at least one criterion is satisfied.

Randomised trial of efficacy of SPf66 vaccine against Plasmodium falciparum malaria in children in southern Tanzania

SummaryEffective, safe antimalarial vaccines have proved elusive. The synthetic polypeptide SPf66 vaccine is based on pre-erythrocytic and asexual blood-stage proteins of Plasmodium falciparum. We report here a randomised double-blind placebo-controlled trial of the efficacy of the SPf66 vaccine against clinical P falciparum malaria in Idete, southern Tanzania, an area of intense perennial malaria transmission.586 children aged 1-5 years received three doses of vaccine (n=274) or placebo (n=312). The incidence and density of parasitaemia were assessed through repeated cross-sectional surveys on subgroups of children. Morbidity was monitored over a 1 year period through passive case detection in all children plus active case detection in a subgroup of 191. An episode of clinical malaria was defined as measured fever (≥37·5°C) and parasite density >20 000/μL.No severe side-effects were seen and the frequency of mild side-effects after the third dose was less than 6%. The vaccine was highly immunogenic and after three doses all vaccine recipients had detectable anti-SPf66 antibodies: the geometric mean index of response was 8·3 in the vaccine group and 0·7 in the placebo group. The incidence of parasitaemia was similar in both groups. 123 children had at least one episode of clinical malaria during the follow-up period after the third dose and annual incidence rates were 0·25 in the vaccine group and 0·35 in the placebo group. Estimated vaccine efficacy was 31% (95% confidence interval 0-52%; p=0·046). After the third dose there were 6 deaths among the study cohort (1 vaccine, 5 placebo). This study confirms that SPf66 is safe, immunogenic and reduces the risk of clinical malaria among children exposed to intense P falciparum transmission.