HAAA is a well documented and diverse variant of clinical syndrome of aplastic anemia, in which an acute attack of hepatitis leads to the marrow failure and pancytopenia that may be acute or chronic. This disorder has been reported in 2-5% cases in West, 4-10% in Far East and high in area of low socioeconomic status. HAAA is not related to age, sex and severity of hepatitis, predominantly it has been found in children, adolesecent boys and in young aged men. A number of hepatitis viruses manifest the disease symptoms. Amongst the hepatitis viruses, HBV, HCV and HGV seropositivity has been mostly commonly observed in reported cases of HAAA. The causative agent of HAAA can be detected using hematological, biochemical, immunological and virological markers. The clinical features relating to HAAA are pallor and multiple skin bleeding, lymphocytopenia, hypogammaglobulin, low number of CD8/T cell ratio and increased number of cytotoxic cells, neutropenia and fever etc. For HAAA, immunosuppressive therapy is more effective after BM transplantation.  Factors Affecting Intention to Receive and Self-Reported Receipt of 2009 Pandemic (H1N1) Vaccine in Hong Kong: A Longitudinal Study BACKGROUND: Vaccination was a core component for mitigating the 2009 influenza pandemic (pH1N1). However, a vaccination program's efficacy largely depends on population compliance. We examined general population decision-making for pH1N1 vaccination using a modified Theory of Planned Behaviour (TBP). METHODOLOGY: We conducted a longitudinal study, collecting data before and after the introduction of pH1N1 vaccine in Hong Kong. Structural equation modeling (SEM) tested if a modified TPB had explanatory utility for vaccine uptake among adults. PRINCIPAL FINDINGS: Among 896 subjects who completed both the baseline and the follow-up surveys, 7% (67/896) reported being “likely/very likely/certain” to be vaccinated (intent) but two months later only 0.8% (7/896) reported having received pH1N1 vaccination. Perception of low risk from pH1N1 (60%) and concerns regarding adverse effects of the vaccine (37%) were primary justifications for avoiding pH1N1 vaccination. Greater perceived vaccine benefits (β = 0.15), less concerns regarding vaccine side-effects (β = −0.20), greater adherence to social norms of vaccination (β = 0.39), anticipated higher regret if not vaccinated (β = 0.47), perceived higher self-efficacy for vaccination (β = 0.12) and history of seasonal influenza vaccination (β = 0.12) were associated with higher intention to receive the pH1N1 vaccine, which in turn predicted self-reported vaccination uptake (β = 0.30). Social norm (β = 0.70), anticipated regret (β = 0.19) and vaccination intention (β = 0.31) were positively associated with, and accounted for 70% of variance in vaccination planning, which, in turn subsequently predicted self-reported vaccination uptake (β = 0.36) accounting for 36% of variance in reported vaccination behaviour. CONCLUSIONS/SIGNIFICANCE: Perceived low risk from pH1N1 and perceived high risk from pH1N1 vaccine inhibited pH1N1 vaccine uptake. Both the TPB and the additional components contributed to intended vaccination uptake but social norms and anticipated regret predominantly associated with vaccination intention and planning. Vaccination planning is a more significant proximal determinant of uptake of pH1N1 vaccine than is intention. Intention alone is an unreliable predictor of future vaccine uptake. Influenza contributes significantly to worldwide morbidity and mortality [1] . Periodically, influenza viruses mutate into antigenically-different strains leading to global pandemics [2] . The 2009 influenza pandemic (pH1N1) was caused by a triple reassortment of human, swine and avian influenza viruses [3] . Vaccination is the most effective intervention for preventing influenza [4] and a core part of national pandemic plans for pandemic mitigation. Lead times of at least 6 months in producing a vaccine against a novel strain means that while vaccines may be unavailable in time to prevent the first wave of a pandemic [5, 6] , effective public uptake of a vaccine may mitigate subsequent waves [7] .