Vaccine efficacy didn’t appear to decrease over time. In addition to one breakthrough an infection that was seen in a vaccinated participant through the initial study, six more breakthrough infections occurred in vaccinated individuals through the extended follow-up research. The immune responses to the vaccine in individuals with breakthrough attacks are unknown, which makes it impossible to determine the level of antibody protection. In a previous research where we assessed the association between antibody level and the risk of subclinical hepatitis E disease,9 we estimated a marginal antibody level may prevent infection in 74 percent of persons subjected to HEV.If any of these covariates are correlated with age, for example, there might be a confounding of the consequences of age on the risk of transmission. Censoring of the data is another limitation. Inside our study, the length of home follow-up was only seven days. Although our estimation procedure accounts for this censoring, it does so by assuming an operating form for the serial interval distribution, which determines the probability associated with the tail of the distribution. Our estimates of the serial interval should be interpreted in this light. Such a scholarly study would require large numbers of households to attain sufficient power for inference. Another limitation of our research is that secondary situations weren’t confirmed by laboratory tests. It is therefore likely that a few of the secondary instances were not cases of 2009 H1N1 influenza.