Comparison of the pandemic H1N1 2009 experience in the Southern Hemisphere with pandemic expectations

Systematic review of influenza A(H1N1)pdm09 virus shedding: duration is affected by severity, but not age

Duration of viral shedding following infection is an important determinant of disease transmission, informing both control policies and disease modelling. We undertook a systematic literature review of the duration of influenza A(H1N1)pdm09 virus shedding to examine the effects of age, severity of illness and receipt of antiviral treatment. Studies were identified by searching the PubMed database using the keywords ‘H1N1’, ‘pandemic’, ‘pandemics’, ‘shed’ and ‘shedding’. Any study of humans with an outcome measure of viral shedding was eligible for inclusion in the review. Comparisons by age, degree of severity and antiviral treatment were made with forest plots. The search returned 214 articles of which 22 were eligible for the review. Significant statistical heterogeneity between studies precluded meta-analysis. The mean duration of viral shedding generally increased with severity of clinical presentation, but we found no evidence of longer shedding duration of influenza A(H1N1)pdm09 among children compared with adults. Shorter viral shedding duration was observed when oseltamivir treatment was administered within 48 hours of illness onset. Considerable differences in the design and analysis of viral shedding studies limit their comparison and highlight the need for a standardised approach. These insights have implications not only for pandemic planning, but also for informing responses and study of seasonal influenza now that the A(H1N1)pdm09 virus has become established as the seasonal H1N1 influenza virus.

The pandemic H1N1 influenza experience

The pandemic H1N1 influenza that began in Mexico in the spring of 2009 spread rapidly to southern California within days and around the world within a few months. Because the genetic make-up of the new virus was novel, several months of lead-in time were required before a suitable vaccine for human use could be produced and distributed. The effort to confront the virus on the part of the World Health Organization which included almost every nation on earth and a vast array of scientists and public health officials was extensive and timely. However, it was the moderate severity of the virus itself that saved global public health from catastrophe. Because of the extensive publicity and research that occurred during the H1N1 pandemic, many lessons were learned that will be useful in confronting future influenza pandemics. A "One Health" approach to prevent, detect, and combat future pandemics is essential.