Research Highlight

Pandemic H1N1 deadlier than seasonal cousin

doi:10.1038/nindia.2011.48 Published online 31 March 2011

The inability to induce a strong immune response makes the pandemic H1N1 (pH1N1) virus deadlier, more transmissible and pathogenic than its seasonal cousin H1N1, researchers say.

The novel pH1N1 influenza virus – a triple reassortant comprising genes derived from avian, human, and swine viruses – caused havoc across the world during 2009 and 2010. The virus, antigenically different from the seasonal H1N1 strains, continues to affect some countries.

To better understand the risk posed by the pH1N1, the researchers studied the host gene expression response to the Indian isolate of pH1N1 infection and compared it with seasonal H1N1 infection. The response was studied at four different time points after infection.

They found that pH1N1 induced immune response earlier than seasonal H1N1 viruses, but at the later stages of infection there was a suppression of host immune responses.

The infection with pH1N1 resulted in considerable decrease in the expression of cytokine and other immune genes namely IL8, STAT1, B2M and IL4 compared to seasonal H1N1.

The researchers attribute the high transmissibility of pH1N1 virus in the year 2009-2010 to its better subversion of host immune responses compared to the seasonal influenza viruses. Lack of earlier immunity to pH1N1 virus also made it more pathogenic than seasonal H1N1, they suggest.


  1. Mukherjee, S. et al. Pandemic (H1N1) 2009 influenza virus induces weaker host immune responses in vitro: a possible mechanism of high transmissibility. Virol. J. doi: 10.1186/1743-422X-8-140 (2011)