Electronic Nudges for Influenza Vaccination—Reply

In Reply We appreciate the Letter from Ms Wu and colleagues about our trial. Vaccination behavior is known to be influenced by multiple factors, and we completely agree that invitation timing, geographical accessibility to vaccination sites, and prior vaccination beliefs and experiences may be significant determinants. These factors were not directly incorporated into the interventions in our trial as we primarily focused on testing the delivery method and varying letter content across groups; however, owing to the randomized design, we would expect potential confounders such as geographical location and prior vaccination beliefs and experiences to be evenly distributed across groups. In addition, because all intervention letters in the trial were delivered on the same date (September 24, 2023), further analyses of the effects of differential invitation timing were not possible but should be investigated in future efforts. While Danish registries contain data across numerous domains, they do not contain detailed information about prior vaccination experiences or individual risk perception. We were therefore unable to include these data in our analyses. Interestingly, in another recent trial, offering free round-trip Lyft rides to vaccination sites in an attempt to decrease geographical barriers to vaccination did not result in increased vaccination rates.

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Electronic Nudges for Influenza Vaccination

To the Editor In a recent study, electronically delivered nudges directed at patients with chronic diseases significantly improved influenza vaccination uptake, although the magnitude of improvement was limited. This result may have reflected the selection characteristics of the study population, which included patients with chronic diseases who likely had high baseline awareness of the benefits of influenza vaccination. Consequently, high baseline intent may have attenuated the intervention’s effect. The “repeated letter” group achieved the greatest increase, improving by 13.5%, while other messaging frames, such as “cardiovascular benefits” and “respiratory benefits,” yielded gains of approximately 11.0% to 11.9%. These increases were modest relative to the control group, suggesting a ceiling effect in populations with preexisting intent to be vaccinated.

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Accuracy of individual signs and symptoms and case definitions for the diagnosis of influenza in different age groups: a systematic review with meta-analysis

Objective
The objective of this study is to perform a comprehensive systematic review and meta-analysis of the accuracy of signs, symptoms and case definitions for the diagnosis of influenza.

Design
Systematic review and meta-analysis of diagnostic accuracy.

Setting
Inpatient or outpatient setting.

Participants
Three databases (PubMed, CINAHL and EMBASE) were searched through February 2024 for studies of clinical diagnosis of influenza using prospective data collection and a high-quality reference standard. Data were abstracted by researchers working in parallel and resolving discrepancies by discussion.

Primary and secondary outcome measures
Quality was assessed using QUADAS-2. Summary estimates (or ranges) of sensitivity and specificity, likelihood ratio (LR), the Youden Index and the area under the receiver operating characteristic curve were calculated.

Results
The final meta-analysis included 67 studies, each with between 119 and 155 866 participants. Most were judged to be low risk of bias. The signs and symptoms with the highest overall accuracy for all studies based on the Youden Index were any fever (0.32), overall clinical impression (0.28), coryza (0.25), cough and fever (0.25), and measured fever (0.25). Accuracy varied widely by age group. Only the overall clinical impression had a positive LR greater than 2.0. Cough was the most sensitive finding (0.92) with a negative LR of 0.28 in adults. The absence of any fever also had a low negative LR (0.30). The Centers for Disease Control and Prevention (CDC) definition of influenza-like illness (ILI) had good specificity but poor sensitivity in adults, while in infants, it had good sensitivity but widely varying specificity. The European CDC and WHO case definitions for ILI had modest sensitivity and specificity.

Conclusions
Individual signs and symptoms, their combinations, and ILI case definitions have very limited accuracy for identifying persons with influenza. More accurate surveillance and diagnosis will require the development and validation of accurate risk scores or greater use of point-of-care testing.

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The Limited Role for Antiviral Therapy in Influenza

Influenza is associated with substantial morbidity and mortality. Given this, antiviral therapy is commonly prescribed in an effort to prevent these outcomes. We therefore found it surprising that antivirals seem to make little difference for individuals with influenza in outpatient settings, even in the optimized setting of randomized clinical trials.

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