***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Overdispersion is a common feature of models of biological data , but research ers often fail to model the excess variation driving the overdispersion , result ing in biased parameter estimates and st and ard errors . Quantifying and modeling overdispersion when it is present is therefore critical for robust biological inference . One means to account for overdispersion is to add an observation-level r and om effect ( OLRE ) to a model , where each data point receives a unique level of a r and om effect that can absorb the extra-parametric variation in the data . Although some studies have investigated the utility of OLRE to model overdispersion in Poisson count data , studies doing so for Binomial proportion data are scarce . Here I use a simulation approach to investigate the ability of both OLRE models and Beta-Binomial models to recover unbiased parameter estimates in mixed effects models of Binomial data under various degrees of overdispersion . In addition , as ecologists often fit r and om intercept terms to models when the r and om effect sample size is low ( < 5 levels ) , I investigate the performance of both model types under a range of r and om effect sample sizes when overdispersion is present . Simulation results revealed that the efficacy of OLRE depends on the process that generated the overdispersion ; OLRE failed to cope with overdispersion generated from a Beta-Binomial mixture model , leading to biased slope and intercept estimates , but performed well for overdispersion generated by adding r and om noise to the linear predictor . Comparison of parameter estimates from an OLRE model with those from its corresponding Beta-Binomial model readily identified when OLRE were performing poorly due to disagreement between effect sizes , and this strategy should be employed whenever OLRE are used for Binomial data to assess their reliability . Beta-Binomial models performed well across all context s , but showed a tendency to underestimate effect sizes when modelling non-Beta-Binomial data . Finally , both OLRE and Beta-Binomial models performed poorly when models contained < 5 levels of the r and om intercept term , especially for estimating variance components , and this effect appeared independent of total sample size . These results suggest that OLRE are a useful tool for modelling overdispersion in Binomial data , but that they do not perform well in all circumstances and research ers should take care to verify the robustness of parameter estimates of OLRE models ABSTRACT The serogroup A meningococcal conjugate vaccine MenAfriVac has the potential to confer herd immunity by reducing carriage prevalence of epidemic strains . To better underst and this phenomenon , we initiated a meningococcal carriage study to determine the baseline carriage rate and serogroup distribution before vaccine introduction in the 1- to 29-year old population in Burkina Faso , the group chosen for the first introduction of the vaccine . A multiple cross-sectional carriage study was conducted in one urban and two rural districts in Burkina Faso in 2009 . Every 3 months , oropharyngeal sample s were collected from > 5,000 r and omly selected individuals within a 4-week period . Isolation and identification of the meningococci from 20,326 sample s were performed by national laboratories in Burkina Faso . Confirmation and further strain characterization , including genogrouping , multilocus sequence typing , and porA-fetA sequencing , were performed in Norway . The overall carriage prevalence for meningococci was 3.98 % ; the highest prevalence was among the 15- to 19-year-olds for males and among the 10- to 14-year-olds for females . Serogroup Y dominated ( 2.28 % ) , followed by serogroups X ( 0.44 % ) , A ( 0.39 % ) , and W135 ( 0.34 % ) . Carriage prevalence was the highest in the rural districts and in the dry season , but serogroup distribution also varied by district . A total of 29 sequence types ( STs ) and 51 porA-fetA combinations were identified . The dominant clone was serogroup Y , ST-4375 , P1.5 - 1,2 - 2/F5 - 8 , belonging to the ST-23 complex ( 47 % ) . All serogroup A isolates were ST-2859 of the ST-5 complex with P1.20,9/F3 - 1 . This study forms a solid basis for evaluating the impact of MenAfriVac introduction on serogroup A carriage A prospect i ve carriage and serological study was conducted in Burkina Faso during the 2003 meningitis season , which was characterized by hyperendemic Neisseria meningitidis serogroup W135 ( NmW135 ) and serogroup A ( NmA ) disease . Participants were evaluated five times at monthly intervals . In the presence of moderate NmW135 carriage , we found a low prevalence of putatively protective levels of specific immunoglobulin G ( IgG ) and serum bactericidal antibody ( SBA ) against NmW135 . Specific IgG concentrations and SBA titers against NmA were relatively high in this recently vaccinated population , while no NmA carriage was detected . NmW135 carriage infrequently induced protective immunity against reference or homologous strains , while natural immunity against NmW135 was frequently lost . A vaccine that is effective against W135 will be beneficial for sub-Saharan Africa Summary In a study of carriage of Neisseria meningitidis in family contacts of patients with group A meningococcal meningitis in the African meningitis belt an overall carrier rate of 17 per cent was observed . The rate was higher in the younger age groups ( 5–19 years ) .  No overall sex difference was observed . The carrier rate was significantly higher in the contacts who had been sleeping in the same room as the patient . Rifampicin  reduced the carrier rate from 20 per cent to five per cent within two weeks of treatment and a further drop of 2·5 per cent was observed four weeks later . The corresponding results for sulphadimidine were 14 , 14 and 10 per cent . More than 90 per cent of the strains isolated were resistant to 50 μg/ml of  sulphadiazine  in vitro . All of the strains initially isolated were sensitive to rifampicin  , but of the 11 strains isolated after treatment with this drug four were partially resistant A combined group A and group C meningococcal polysaccharide vaccine was given to 438 Nigerian schoolboys shortly before an outbreak of group A meningococcal disease occurred in their school . Four months after vaccination the carriage rate of group A meningococci among vaccinated subjects ( 11 % ) was no different from that found among the controls ( 12 % ) , although a good antibody response to both components of the vaccine was observed . One case of group A meningococcal disease was recorded amongst 438 vaccinated subjects while five cases occurred among 874 controls 
    Output:
    
This is consistent with contact studies in Africa , which show that children 10–14 years have the highest frequency of contacts .
Targeting older children in Africa for conjugate vaccination may be effective in reducing meningococcal transmission