The US Centers for Disease Control and Prevention (CDC) have made a startling announcement this week. Two children previously vaccinated for the H1N1 influenza virus have contracted a new strain named H3N2 in what is being called a virus “reassortment.” The good news is both have been treated successfully, but what’s next?

The viruses are similar but not identical to each other, but they are different from eight other H3N2 infections identified in people over the past two years because they both contain the so-called matrix gene from the pandemic H1N1 influenza strain.

The new identified variant contains genes of the H3N2 swine influenza that has been circulating in North American pigs since 1998 as well as the gene from the pandemic virus H1N1, making it a kind of hybrid.

The infected boy had no direct contact with pigs, but his symptoms which included fever, cough, shortness of breath, diarrhea, and sore throat, began two days after he was cared for by someone who’d had direct contact with asymptomatic animals in the preceding weeks.

The girl, on the other hand, had been to an agricultural fair where she had direct exposure to swine. Four days later, she was taken to the hospital with fever, nonproductive cough, and lethargy.

The CDC report states:

“Although reassortment between swine influenza and 2009 influenza H1N1 viruses has been reported in pigs in the United States, this particular genetic combination of swine influenza virus segments is unique and has not been reported previously in either swine or humans, based on a review of influenza genomic sequences publicly available in GenBank. Analysis of data submitted to GenBank via the U.S. Department of Agriculture (USDA) Swine Influenza Virus Surveillance Program subsequent to this case identified two additional influenza H3N2 isolates from swine containing the M gene from the 2009 influenza H1N1 virus. Genome sequencing is underway to completely characterize the genetic composition of these two swine influenza isolates.”

The viruses in these two patients are resistant to amantadine and rimantadine, but are susceptible to the neuraminidase inhibitor drugs oseltamivir and zanamivir. Because these viruses carry a unique combination of genes, no information currently is available regarding the capacity of this virus to transmit efficiently in swine, humans, or between swine and humans.

To detect human infections with animal influenza viruses more effectively, CDC and state and local health departments have strengthened laboratory and epidemiologic procedures to promptly detect sporadic cases such as these.

The CDC concludes:

“The lack of known direct exposure to pigs in one of the two cases described in this report suggests the possibility that limited human-to-human transmission of this influenza virus occurred. Likely transmission of swine-origin influenza H3N2 virus from close contact with an infected person has been observed in past investigations of human infections with swine-origin influenza H3N2 virus, but has not resulted in sustained human-to-human transmission. Preliminary evidence from the investigation of the Indiana case shows no ongoing transmission. No influenza illness has been identified, but if additional chains of transmission are identified rapid intervention is warranted try to prevent further spread of the virus.”

Written by Sy Kraft