Convalescent Plasma Treatment Reduced Mortality by 50% in Patients with Severe Swine Flu

Treatment using the convalescent plasma from donors who recovered from the swine flu can reduce the mortality rate from severe cases, researchers from the Infectious Diseases and Microbiology team, headed by Professor YUEN Kwok-yung, Henry Fok Professor in Infectious Diseases, Head of the Department of Microbiology and Dr. Ivan HUNG Fan-ngai, Clinical Assistant Professor of the Department of Medicine, The University of Hong Kong Li Ka Shing Faculty of Medicine have found. Results of this project will appear in the forthcoming issue of the journal Clinical Infectious Diseases.

During April to December 2009, more than 30,000 patients were laboratory-confirmed to have contracted the human swine influenza (swine flu, or pandemic H1N1 2009) in Hong Kong. Among them, 1% had severe presentation and required hospitalization and respiratory support. 85 patients eventually died due to this novel infection. In 2009, the large-scale human swine flu vaccination programme targeting the high-risk population was launched by the Department of Health in Hong Kong. However, the vaccination uptake rate was low due to the early report of a case who developed Guillain-Barre syndrome following vaccination. Besides, a significant proportion of the patients presented with severe diseases were healthy young patients with no risk factor, and therefore not candidate for vaccination. Many of these severe cases were late presenters and failed to receive treatment within the optimal 48-hour treatment period for antiviral agents like Tamiflu.

In order to treat these severe cases, especially those young late presenters, the team took experience from treating patients with Spanish influenza. These small-scale studies suggested that convalescent plasma therapy might be beneficial. A prospective cohort study was conducted by recruiting adult patients with severe pandemic H1N1 2009 infection requiring intensive care and offering treatment with convalescent plasma with a neutralizing antibody titer of ≥ 1:160, harvested by plasmapheresis from the Red Cross Transfusion Service, from donors who recovered from the pandemic H1N1 2009 infection. The patients were divided into treatment and control (non-treatment) groups which were matched by age, sex, and disease severity scores (20 patients vs. 73 patients). Mortality in the treatment group was significantly lower than in the control group (20.0% vs. 54.8%; P<0.01). The study also demonstrated that plasma treatment significantly lowered the day 3-7 respiratory tract viral load and cytokine level when compared with the control group (P<0.05)

In conclusion, this study has demonstrated that convalescent plasma treatment is crucial for patients with severe H1N1 2009 infection. The treatment effectively reduced the viral load and dampened the cytokine response with reduced mortality. It also overcomes the problems of emergence of resistant strains and late presenters. A double-blind randomized controlled trial with hyperimmune intravenous immunoglobulin on patients with severe influenza infection is warranted in the future.