Unbeknownst to most there is constant influenza monitoring occurring globally. This allows us to estimate the strains most likely to circulate through human populations, develop vaccines targeted for the three most likely strains and simply prepare for annual influenza seasons. Prior to the culmination of candidate vaccine strains is monitoring animal populations where most, if not all influenza strains originate, mutate and become infectious to humans where additional mutations occur and so on. Some strains never make it into humans but many do.
One such influenza strain is being monitored in swine populations, H3N2 and its variant H3N2v has been infecting humans. Thus far, human infections have been reported in 8 states since July 2011, Hawaii, Illinois, Ohio, Iowa, Maine, Pennsylvania, Utah and West Virginia. All infected have had probable or definite exposure to infected swine however there have been three cases that were deemed as human to human transmitted. Although human-human transmission appears to be very limited, H3N2v does contain the M or matrix gene from the 2009 H1N1 influenza strain which may confer increased transmissibility to and between humans.
Since 90% and more pigs tested have been found to be infected with H3N2, the CDC is recommending that those who are vulnerable to influenza complications such as infants, young children, pregnant women, elderly and immune-compromised people avoid contact with pigs such as farms and fairs.