The 2009 Pandemic Influenza Virus: Where Did It Come from, Where Is It Now, and Where Is It Going?

Abstract

Around 2008 or 2009, an influenza A virus that had been circulating undetected in swine entered human population. Unlike most swine influenza infections of humans, this virus established sustained human-to-human transmission, leading to a global pandemic. The virus responsible, 2009 pandemic H1N1 (H1N1pdm), is the result of multiple reassortment events that brought together genomic segments from classical H1N1 swine influenza virus, human seasonal H3N2 influenza virus, North American avian influenza virus, and Eurasian avian-origin swine influenza viruses. Genetically, H1N1pdm possesses a number of unusual features, although the genomic characteristics that permitted sustained human-to-human transmission are yet unclear. Human infection with H1N1pdm has generally resulted in low mortality, although certain subgroups (including pregnant women, people with some chronic medical conditions, morbidly obese individuals, and immunosuppressed people) have significantly higher risk of severe disease. As H1N1pdm has spread throughout the human population it continued to evolve. It has also reentered the swine population as a circulating pathogen, and has been transiently identified in other species such as turkeys, cats, and domestic ferrets. Most genetic changes in H1N1pdm to date have not been clearly linked to changes in antigenicity, disease severity, antiviral drug resistance, or transmission efficiency. However, the rapid evolution rate characteristic of influenza viruses suggests that changes in antigenicity are inevitable in future years. Experience with this first pandemic of twenty-first century reemphasizes the importance of influenza surveillance in animals as well as humans, and offers lessons to develop and enhance our ability to identify potentially pandemic influenza viruses in the future.

Laboratory Investigation and Molecular Epidemiology of H1N1pdm Virus 2012-2013 from India

“…This study clearly indicates that the cosmopolitan clade VII viruses are continuously circulating in India. This molecular epidemiology information will facilitate better pandemic planning and response capacity for future epidemiological surveillance in Indian subcontinent and abroad [22][23][24][25][26][27][28][29].…”

Exploiting virus-like particles as innovative vaccines against emerging viral infections

“…Moreover, there has been potential zoonotic transmission from domestic or wild animals, some of which serves as mixing vessels for the generation of novel influenza. In fact, the 2009 pandemic H1N1 influenza turned out to be a genetic reassortment among four different viral species of avian, swine, and human origin (Shapshak et al, 2011;York and Donis, 2013). Although direct human-to-human transmission is not officially announced, the highly pathogenic avian influenza (HPAI) H5N1 virus remains on the watch list, especially when considering extremely high mortality among humans.…”

Multiple amino acid mutations in viral RNA polymerase may synergistically enhance the transmissibility and/or virulence of the 2009 pandemic influenza (H1N1) virus

“…When challenged by the host immune system, such changes provide the candidate strains with new characteristics for natural selection. The evolutionary history of the H1N1 influenza A virus suggests that the 2009 pandemic virus had undergone a long period of evolution in animals and humans, including changes in antigenicity, long before reaching the level of transmissibility and virulence required to cause the pandemic in 2009 (York and Donis, 2012). It was reported that the avian influenza virus with E627K substitution in PB2 could infect human cells (Hatta et al, 2007;Subbarao et al, 1993).…”