#13,838
Just under a year ago, in Netherlands Reports A Reassorted H1N2 Flu Virus, we looked at a single detection of a reassorted H1N2 virus in a hospitalized patient, who had since recovered.
Influenza reassortment - also known as Antigenic Shift - is something we've covered often in the blog, albeit mostly in birds, swine, and other mammals. This reshuffling of influenza genes is the primary force behind the creation of novel or pandemic flu (see NIAID Video: How Influenza Pandemics Occur).
Our biggest concern is of seeing a humanized (seasonal H1N1 or H3N2) influenza virus reassort with a novel flu, like H7N9 or H5N1, potentially producing a highly virulent and easily transmitted hybrid (see EID Journal: Human Co-Infection with Avian and Seasonal Influenza Viruses, China).
While less concerning, reassortments between currently circulating seasonal flu viruses can also occur.
- In November of 2015 in J Clin Virol: Influenza Co-Infection Leading To A Reassortant Virus we looked at just such an occurrence. A co-infection between seasonal H3N2 and H1N1pdm09 in a 3 year old Cambodian boy which led to a new, reassortant H3N2 virus.
- In 2011 we saw a similar co-infection in Canada that led to the creation of a unique hybrid reassorted virus (see pH1N1 – H3N2 A Novel Influenza Reassortment) in a 16-month old boy from the Greater Toronto Area.
While a minor player in most regions, H1N2 was the predominant Influenza A(H1) virus reported during the UK's 2001–02 influenza season (cite).These were human-origin H1N2 viruses, not to be confused with the swine-origin variant H1N2 viruses that have circulated in pigs for decades and that we've seen occasionally jump to humans over the past decade.
Yesterday the CDC published the following summary and risk assessment of another reassorted H1N2 virus, detected this time in Sweden.
Influenza A (H1N2) Reassortant Infection in Sweden
Background:
On Friday, January 25, 2019, Sweden reported a human infection with an influenza A(H1N2) virus. The virus likely resulted from a reassortment event between circulating human seasonal influenza A(H1N1)pdm09 and influenza A(H3N2) viruses. The World Health Organization (WHO) first reported the case on its regional surveillance site FluNewsEurope.
Influenza Virus Reassortment:
Reassortment happens when two or more influenza viruses infect a single host and exchange gene segments. Genetic sequencing showed that the A(H1N2) virus in Sweden was a reassortant containing a similar H1 hemagglutinin gene as circulating, seasonal A(H1N1)pdm09 viruses and an N2 neuraminidase gene similar to circulating, seasonal A(H3N2) viruses.
Human infections with reassortant A(H1N2) viruses have occurred rarely in the past, but these were reassortants of the human, seasonal A(H1N1) virus that circulated prior to emergence of the 2009 A(H1N1)pdm09 virus that triggered a pandemic in 2009. This is the second reassortant of seasonal A(H1N1)pdm09 and seasonal A(H3N2) viruses reported.
In 2018, a human infection caused by a reassortant A(H1N2) virus was reported in the Netherlands. Laboratory experiments with previous A(H1N1) reassortants in ferret models suggested that these viruses had limited capacity for transmission, however human-to-human spread is still possible.
Risk Assessment:
This A(H1N2) reassortant virus is thought to pose a health risk similar to other seasonal influenza viruses. The virus has not been detected beyond this one person and current seasonal influenza vaccines would likely offer protection against this virus. Additionally, this virus does not have markers associated with resistance to the neuraminidase inhibitor class of antiviral drugs and, thus, should be susceptible to treatment with the currently recommended drugs oseltamivir, zanamivir and peramivir.
While these hybrid reassortments of seasonal flu are rare, as any virologist will tell you; shift happens.
