Observational methods in epidemiologic assessment of vaccine effectiveness.

National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead, NSW.
Communicable diseases intelligence 02/2002; 26(3):451-7.
Source: PubMed


Observational methods are important in the measurement of vaccine effectiveness (VE) as experimental designs cannot be used for measurement of vaccines already on the vaccination schedule. Furthermore, efficacy measured in clinical trials under ideal conditions may differ to effectiveness in the field under non-ideal conditions and in different populations. In addition to post-licensure surveillance, observational VE studies are particularly important when disease incidence does not predictably decrease with increased vaccine coverage, when high proportions of vaccine failure among reported cases suggest a problem with the vaccine or when issues arise that were not predicted in pre-licensure evaluations. Commonly used study types for evaluating VE include cohort studies, household contact studies, case-control studies, the screening method and case-cohort studies. There are many potential biases in all observational VE studies which should be considered in the study design and analysis stage. Of the five observational study types reviewed, cohort studies undertaken during an outbreak investigation offer the simplest means of VE estimation and is the preferred study design where the situation permits. Where this is not possible the screening method is the most economical and rapid method. It is essential that the effectiveness of all vaccination programs be evaluated. As new vaccines are introduced to the schedule, booster doses are added and the timing of doses changed, the role of observational methods in the evaluation of VE will become even more important. To date, few observational VE studies have been undertaken in Australia, suggesting the under-utilisation of these methods.

Download full-text


Available from: Siranda Torvaldsen, Oct 05, 2015
58 Reads
  • Source
    • "These studies implied that immunization with J-5 bacterin reduced the severity of local and systemic signs of clinical mastitis following intramammary challenge. Efficacy of vaccination against Staphylococcus aureus and CNS is a very different concept than efficacy of vaccination against E. coli (Torvaldsen and McIntyre, 2002). Whereas with E. coli the vaccine is mostly expected to reduce severity of infection, with Staph. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to evaluate vaccine efficacy of a commercial vaccine (Startvac, Hipra Spain) aimed at reducing intramammary infections (IMI) with Staphylococcus aureus and coagulase-negative staphylococci under field conditions. During the 21-mo duration of the study, 1,156 lactations from 809 cows were enrolled in 2 herds. During the first phase of the trial, all cows that were due to calve were vaccinated until approximately 50% of cows in the milking herd were vaccinated (at ∼6 mo). At that point, when 50% vaccination coverage was reached, cows that were due to calve were randomly assigned to be vaccinated or left as negative controls. Cure rate, rate of new infection, prevalence, and duration of infections were analyzed. Vaccination resulted in a moderate reduction in incidence of new staphylococcal IMI and a more pronounced reduction in duration of IMI associated with reduction of the basic reproduction ratio of Staph. aureus by approximately 45% and of coagulase-negative staphylococci by approximately 35%. The utilization of vaccine in combination with other infection-control procedures, such as excellent milking procedures, treatment, segregation, and culling of known infected cattle, will result in an important reduction in incidence and duration of intramammary staphylococcal infections.
    Journal of Dairy Science 05/2014; 97(8). DOI:10.3168/jds.2014-8008 · 2.57 Impact Factor
  • Source
    • "Vaccine effectiveness (VE) is the risk reduction attributed to vaccination estimated from observational studies from measurements of the incidence of disease in vaccinated and unvaccinated individuals.13 In a case-control study, the VE for the prevention of AMI is estimated from the Odds Ratio (OR) using the formula: (1- OR)×100.14 We used the adjusted OR of the association between influenza vaccination and AMI, obtained from the final logistic regression model. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Abundant, indirect epidemiological evidence indicates that influenza contributes to all-cause mortality and cardiovascular hospitalisations with studies showing increases in acute myocardial infarction (AMI) and death during the influenza season. To investigate whether influenza is a significant and unrecognised underlying precipitant of AMI. Case-control study. Tertiary referral hospital in Sydney, Australia, during 2008 to 2010. Cases were inpatients with AMI and controls were outpatients without AMI at a hospital in Sydney, Australia. Primary outcome was laboratory evidence of influenza. Secondary outcome was baseline self-reported acute respiratory tract infection. Of 559 participants, 34/275 (12.4%) cases and 19/284 (6.7%) controls had influenza (OR 1.97, 95% CI 1.09 to 3.54); half were vaccinated. None were recognised as having influenza during their clinical encounter. After adjustment, influenza infection was no longer a significant predictor of recent AMI. However, influenza vaccination was significantly protective (OR 0.55, 95% CI 0.35 to 0.85), with a vaccine effectiveness of 45% (95% CI 15% to 65%). Recent influenza infection was an unrecognised comorbidity in almost 10% of hospital patients. Influenza did not predict AMI, but vaccination was significantly protective but underused. The potential population health impact of influenza vaccination, particularly in the age group 50-64 years, who are at risk for AMI but not targeted for vaccination, should be further explored. Our data should inform vaccination policy and cardiologists should be aware of missed opportunities to vaccinate individuals with ischaemic heart disease against influenza.
    Heart (British Cardiac Society) 08/2013; 99(24). DOI:10.1136/heartjnl-2013-304320 · 5.60 Impact Factor
  • Source
    The Lancet 06/2005; 365(9477):2086; author reply 2087. DOI:10.1016/S0140-6736(05)66725-6 · 45.22 Impact Factor
Show more