Lessons Learnt from (HIN1)2009 Influenza Pandemic for Preparedness Against Future Pandemics

Pandemic (H1N1) 2009 was relatively mild with less severe disease burdens and social impact. Pandemic (H1N1)pdm09 virus itself was low pathogenic, similar to seasonal flu viruses and different from H5N1 highly pathogenic avian influenza viruses. Most people had acquired immunity to Spanish flu or former seasonal H1N1 flu viruses, which was cross-protective, in part, against H1N1pdm09 virus. The pandemic started in the North America, where US CDC detected and identified the causative virus rapidly, sharing information with WHO to take immediate responses. Most countries had been prepared, more or less, against a possible pandemic by H5N1. H1N1pdm09 virus hardly underwent antigenic drift and the pandemic vaccine remained matched and effective. The virus was susceptible to neuraminidase inhibitors and drug-resistant viruses did not spread, unlike former seasonal H1N1 virus during 2007-2009. The pandemic virus did not increase the pathogenicity, unlike Spanish flu in 1918/19. Finally, disease burdens and social impact remained far below previous assumptions against a possible H5N1 pandemic. On the other hand, pandemic vaccine production and supply were delayed and insufficient and much confusion occurred due to misleading by health authorities and media. It appeared clear that implementation of pandemic preparedness plans had been suboptimal in many settings.

During the pandemic (H1N1)2009, H5N1 highly pathogenic avian influenza continued to spread in several areas causing human infections. WHO is keeping its pandemic alert level Phase 3. Both H1N1pdm09 and H5N1 viruses were shown to infect pigs in China and Indonesia and therefore, gene reassortment between the viruses may occur in pigs or humans. Risk of an H5 pandemic still remains or is increasing, which will cause extremely heavy disease burdens and social disruptions.

We should also learn much from the devastating earthquakes and tsunami and the resultant nuclear power plant accident, which occurred at much severer levels far beyond the government’s “optimistic assumptions”, bases for the suboptimal preparedness. The worst thing we can do is not prepare for a worst case scenario and think it will not happen. We must be prepared against a worst-case scenario of pandemic influenza caused by a highly pathogenic virus.