New study shows H1N1 similar to seasonal H3N2

While the strange spring emergence and summer activity of the 2009 novel H1N1 virus raised suspicions that the virus’ transmission might differ from typical strains, a new research study has shown that it was similar to seasonal H3N2 viruses.

Virologist Dr. Peter Palese, as part of a group from Mount Sinai School of Medicine in New  York Cit, compared the transmission patterns of 2009 H1N1 and seasonal H3N2 viruses in guinea pigs, CIDRAP News reports. The findings appeared Wednesday in the Journal of Virology early online edition, according to.

The group ran several aerosol transmission experiments using multiple different environmental conditions to compare to their 2007 study that showed aerosol H3N2 transmission depended on cold and dry conditions.

In each series of the test, experimentally infected guinea pigs were placed with uninfected animals in the same environmental chamber, according to CIDRAP News.

Both viruses were found to transmit well at 65 percent relative humidity and 68 degrees. When the relative humidity was increased to 80 percent, there was no transmission of the 2009 H1N1 virus and only one of the four exposed guinea pigs contracted the H3N2 virus. Dry conditions with warmer temperatures also led to low levels of viral transmission. Neither virus transmitted when conditions were warm and humid.

Since the sensitivity of the 2009 H1N1 virus to humidity and temperature was similar to the H3N2 virus, researchers have attributed the unusual seasonality during early-fall and summer of the 2009 H1N1 virus to the population’s lack of pre-existing immunity, CIDRAP News reports. The researchers noted that spring flu waves have occurred before in previous pandemics and that availability of susceptible hosts is a key driver in transmission.

“Thus, perhaps in the absence of widespread immunity, the humidity and temperature requirements needed to achieve sustained transmission of influenza virus became less stringent,” the researchers wrote in their report, according to CIDRAP News.