Review Article

Abstract

Background The fraction of persons with influenza virus infection who do not report any signs or symptoms throughout the course of infection is referred to as the asymptomatic fraction. Methods We conducted a systematic review and meta-analysis of published estimates of the asymptomatic fraction of influenza virus infections. We found that estimates of the asymptomatic fraction were reported from two different types of studies: first, outbreak investigations with short-term follow-up of potentially exposed persons and virologic confirmation of infections; second, studies conducted across epidemics typically evaluating rates of acute respiratory illness among persons with serologic evidence of infection, in some cases adjusting for background rates of illness from other causes. Results Most point estimates from studies of outbreak investigations fell in the range 4%–28% with low heterogeneity (I2=0%) with a pooled mean of 16% (95% CI: 13%, 19%). Estimates from the studies conducted across epidemics without adjustment were very heterogeneous (point estimates 0%–100%; I2=97%), while estimates from studies that adjusted for background illnesses were more consistent with point estimates in the range 65%–85% and moderate heterogeneity (I2=58%). Variation in estimates could be partially explained by differences in study design and analysis, and inclusion of mild symptomatic illnesses as asymptomatic in some studies. Conclusions Estimates of the asymptomatic fraction are affected by the study design, and the definitions of infection and symptomatic illness. Considerable differences between the asymptomatic fraction of infections confirmed by virologic versus serologic testing may indicate fundamental differences in the interpretation of these two indicators.

Transmissibility of the Influenza Virus during Influenza Outbreaks and Related Asymptomatic Infection in Mainland China, 2005-2013

“…Some studies have shown that the p value of influenza can exceed 75%, and the difference between seasonal and pandemic influenza was not significant [2]. But recently, Leung et al [18] did a systematic review and found that estimates of the p based on outbreak investigations and household transmission studies appeared to provide more homogeneity in estimates of the p , with most point estimates in the range 4%–28% and a pooled mean of 16% (95% CI: 13–19). Our study indicated that the p value of the influenza virus can reach a maximum of 94% and exhibited a mean of 14% (95% CI: 12%–16%) during an outbreak, which was similar to the finding of Leung et al [18]; however, most outbreaks did not include asymptomatic infections.…”

“…But recently, Leung et al [18] did a systematic review and found that estimates of the p based on outbreak investigations and household transmission studies appeared to provide more homogeneity in estimates of the p , with most point estimates in the range 4%–28% and a pooled mean of 16% (95% CI: 13–19). Our study indicated that the p value of the influenza virus can reach a maximum of 94% and exhibited a mean of 14% (95% CI: 12%–16%) during an outbreak, which was similar to the finding of Leung et al [18]; however, most outbreaks did not include asymptomatic infections. Different subtypes appeared to follow similar transmission pattern and this information can be exploited to strategically allocate resources in future prevention and control management.…”

Strong Constraints on Fuzzy Dark Matter from Ultrafaint Dwarf Galaxy Eridanus II

“…The central soliton has some favourable consequences, e.g. its stabilising effect on the cold clump in Ursa Minor [35], a possible explanation for cored density profiles in dSphs [27,[36][37][38] and UFDs [39], help alleviating the "too big to fail" problem [6,40], and an explanation for excess mass in the centre of the MW [41]These observations, as well as other hints from the small-scale structure of DM [6,8,42], point to a preferred FDM mass…”

“…In this range there are no additional constraints from star cluster heating in Eri II. Some authors have argued that m a ∼ O(few)×10 −22 eV is favoured by density profiles of local dSphs [65] and the Milky Way core [66], and may even be favoured by an apparent turn over in the Hubble Frontiers Fields luminosity function [42].…”

Assessing the benefits of early pandemic influenza vaccine availability: a case study for Ontario, Canada

“…After the latent period has elapsed, infected individuals progress to the infectious stage, which can be either symptomatic or asymptomatic. The proportion of asymptomatic infections was set at 25% in the absence of vaccination 24 . The probability of developing symptomatic infection was determined based on the level of individual’s frailty, pre-existing cellular immunity and vaccine-induced protection at the individual level (see Supplementary Information).…”