Estimation of the reproductive number and the serial interval in early phase of the 2009 influenza A/H1N1 pandemic in the USA

Abstract

Background The United States was the second country to have a major outbreak of novel influenza A/H1N1 in what has become a new pandemic. Appropriate public health responses to this pandemic depend in part on early estimates of key epidemiological parameters of the virus in defined populations. Methods We use a likelihood‐based method to estimate the basic reproductive number (R 0) and serial interval using individual level U.S. data from the Centers for Disease Control and Prevention (CDC). We adjust for missing dates of illness and changes in case ascertainment. Using prior estimates for the serial interval we also estimate the reproductive number only. Results Using the raw CDC data, we estimate the reproductive number to be between 2·2 and 2·3 and the mean of the serial interval (μ) between 2·5 and 2·6 days. After adjustment for increased case ascertainment our estimates change to 1·7 to 1·8 for R 0 and 2·2 to 2·3 days for μ. In a sensitivity analysis making use of previous estimates of the mean of the serial interval, both for this epidemic (μ = 1·91 days) and for seasonal influenza (μ = 3·6 days), we estimate the reproductive number at 1·5 to 3·1. Conclusions With adjustments for data imperfections we obtain useful estimates of key epidemiological parameters for the current influenza H1N1 outbreak in the United States. Estimates that adjust for suspected increases in reporting suggest that substantial reductions in the spread of this epidemic may be achievable with aggressive control measures, while sensitivity analyses suggest the possibility that even such measures would have limited effect in reducing total attack rates.

Prevalence of seroprotection against the pandemic (H1N1) virus after the 2009 pandemic

“…Various estimates of R o have been derived for the pandemic (H1N1) virus, ranging up to 3.0 in the setting of a school outbreak, but are generally between 1.5 and 2.0 on average. [16][17][18][19][20] On that basis, community-level protection against the pandemic (H1N1) virus in the range of 33%-50% overall would be enough to prevent an epidemic, assuming random mixing of people of different ages and homogeneous immunity. School-aged children, however, are thought to contribute disproportionately to influenza transmission.…”

The Impact of Demographic Variables on Disease Spread: Influenza in Remote Communities

“…In our model, the level of preexisting immunity reduces the overall susceptibility of the population, and therefore R 0 may be higher than the number of secondary cases generated in simulation scenarios. The base transmission probability b base (in the absence of any pre-existing immunity or limitation to disease spread) was tuned such that the average number of secondary infections over the entire sample of realizations was 1.9 24 .…”

Likely effectiveness of pharmaceutical and non-pharmaceutical interventions for mitigating influenza virus transmission in Mongolia

“…The importation of A(H1N1)pdm09-infected cases into border patches was modelled using the time-courses of the 2009 pandemic in neighbouring countries and the relative frequency of border crossings. The basic reproduction rate (R 0 ) used as the baseline in the model was based on epidemiological observations in other countries, [15][16][17][18][19] but a wide range of values, including more severe scenarios with R 0 varying around 2, was explored. The data were modelled and graphically displayed using Matlab (MathWorks Inc., Natick, USA).…”