tetano
Editor, Senior Moderator
Vaccine. 2013 Apr 23. pii: S0264-410X(13)00465-9. doi: 10.1016/j.vaccine.2013.04.026. [Epub ahead of print]
The case test-negative design for studies of the effectiveness of seasonal influenza vaccine.
Foppa IM, Haber M, Ferdinands JM, Shay DK.
Source
Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, United States; Battelle Memorial Institute, Atlanta, GA, United States. Electronic address: vor1@cdc.gov.
Abstract
BACKGROUND:
A modification to the case-control study design has become popular to assess vaccine effectiveness (VE) against viral infections. Subjects with symptomatic illness seeking medical care are tested by a highly specific polymerase chain reaction (PCR) assay for the detection of the infection of interest. Cases are subjects testing positive for the virus; those testing negative represent the comparison group. Influenza and rotavirus VE studies using this design are often termed "test-negative case-control" studies, but this design has not been formally described or evaluated. We explicitly state several assumptions of the design and examine the conditions under which VE estimates derived with it are valid and unbiased.
METHODS:
We derived mathematical expressions for VE estimators obtained using this design and examined their statistical properties. We used simulation methods to test the validity of the estimators and illustrate their performance using an influenza VE study as an example.
RESULTS:
Because the marginal ratio of cases to non-cases is unknown during enrollment, this design is not a traditional case-control study; we suggest the name "case test-negative" design. Under sets of increasingly general assumptions, we found that the case test-negative design can provide unbiased VE estimates. However, if there were differences in health care-seeking behavior among cases and non-cases by vaccine status, with strong viral interference or when the vaccine modifies the probability of symptomatic illness VE estimates may be biased.
CONCLUSIONS:
Vaccine effectiveness estimates derived from case test-negative studies are valid and unbiased under a wide range of assumptions. However, if vaccinated cases are less severely ill and seek care less frequently than unvaccinated cases, then an appropriate adjustment for illness severity is required to avoid bias in effectiveness estimates. Viral interference will lead to a non-trivial bias in the vaccine effectiveness estimate from case test-negative studies only when incidence of influenza is extremely high and when duration of transient non-specific immunity is long.
Copyright ? 2013. Published by Elsevier Ltd.
PMID:
23624093
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/23624093
The case test-negative design for studies of the effectiveness of seasonal influenza vaccine.
Foppa IM, Haber M, Ferdinands JM, Shay DK.
Source
Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, United States; Battelle Memorial Institute, Atlanta, GA, United States. Electronic address: vor1@cdc.gov.
Abstract
BACKGROUND:
A modification to the case-control study design has become popular to assess vaccine effectiveness (VE) against viral infections. Subjects with symptomatic illness seeking medical care are tested by a highly specific polymerase chain reaction (PCR) assay for the detection of the infection of interest. Cases are subjects testing positive for the virus; those testing negative represent the comparison group. Influenza and rotavirus VE studies using this design are often termed "test-negative case-control" studies, but this design has not been formally described or evaluated. We explicitly state several assumptions of the design and examine the conditions under which VE estimates derived with it are valid and unbiased.
METHODS:
We derived mathematical expressions for VE estimators obtained using this design and examined their statistical properties. We used simulation methods to test the validity of the estimators and illustrate their performance using an influenza VE study as an example.
RESULTS:
Because the marginal ratio of cases to non-cases is unknown during enrollment, this design is not a traditional case-control study; we suggest the name "case test-negative" design. Under sets of increasingly general assumptions, we found that the case test-negative design can provide unbiased VE estimates. However, if there were differences in health care-seeking behavior among cases and non-cases by vaccine status, with strong viral interference or when the vaccine modifies the probability of symptomatic illness VE estimates may be biased.
CONCLUSIONS:
Vaccine effectiveness estimates derived from case test-negative studies are valid and unbiased under a wide range of assumptions. However, if vaccinated cases are less severely ill and seek care less frequently than unvaccinated cases, then an appropriate adjustment for illness severity is required to avoid bias in effectiveness estimates. Viral interference will lead to a non-trivial bias in the vaccine effectiveness estimate from case test-negative studies only when incidence of influenza is extremely high and when duration of transient non-specific immunity is long.
Copyright ? 2013. Published by Elsevier Ltd.
PMID:
23624093
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/23624093