Thursday, May 30, 2019

Denmark Reports Novel H1N2 Flu Infection


Today, for the third time in just over a year we've a report of a novel H1N2 infection - a reassortment of A/H1N1 and A/H3N2 - from a patient residing in a northern European (see 2019 Swedish report and 2018 Netherlands case) country.
Influenza reassortment - also known as Antigenic Shift - can occur when a host (human, avian, porcine, etc.) is co-infected with two flu viruses, and they swap gene segments. Reassortment is the primary force behind the creation of novel or pandemic flu viruses (see NIAID Video: How Influenza Pandemics Occur).
Luckily, a reassortment of seasonal H1N1 and H3N2 is far less of a concern than a hybrid of seasonal flu and a novel flu virus. Last February the CDC issued the following risk assessment:
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.
Several weeks later, in Eurosurveillance: Novel influenza A(H1N2) Seasonal Reassortant - Sweden, January 2019, we saw the following assessment.
In conclusion, our results support the observation that the currently co-circulating viruses of A(H1N1)pdm09 and seasonal A(H3N2) viruses have the potential to reassort and form new strains that can spread globally causing epidemics. Reassortment between seasonal and zoonotic influenza might lead to novel pandemic strains and therefore molecular surveillance of circulating influenza strains is of high importance.
While human H1N2 infection has only rarely been reported in recent years, we've seen sporadic outbreaks in the past.  These larger outbreaks were reassortments of the old H1N1 virus, not the 2009 H1N1 virus.

In 1988-1989 in China (see Human influenza A (H1N2) viruses isolated from China), and again between 2000 and 2003 in the Northern Hemisphere, we saw the brief appearance of a human H1N2 virus - a reassortment between the old (pre-2009) seasonal H1N1 and H3N2.
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 H1N2v (variant) viruses that have circulated in pigs for decades and that last year was responsible for 14 of the 17 swine variant infections reported to the CDC.

Today's translated report, which was published yesterday on,  comes from information provided by the EU's EWRS: Early Warning and Response System.

A case of influenza due to an unusual virus A (H1N2) in a patient in Denmark 

Published May 29 2019 at 12:01
Author: Claude Hengy
The Danish health authorities have notified May 26, 2019 via EWRS , a case of human influenza A (H1N2) reassortant.

The sample was collected April 11, 2019 in the Danish capital and sent to the Statens Serum Institut institution (SSI) as a sample without special notification of routine surveillance.

The sample was taken in a woman aged 74, not vaccinated against influenza, which had traveled by plane to Croatia before crossing the country, and Bosnia and Herzegovina and Montenegro, between 29 March and 5 April 2019. the patient developed symptoms of respiratory tract infection after returning April 7 and was hospitalized on 11 April. She left the hospital on 13 April.

It is not known if the patient was infected during her trip to Croatia, Bosnia and Herzegovina, Montenegro or during the trip back to Denmark. No other contact or subjects tourists present on the bus in Croatia has developed symptoms.

The levy nasopharyngeal helped highlight an influenza virus A. The whole genome sequencing showed a hemagglutinin gene from the A (H1N1) and a gene pdm09 neuraminidase from the A (H3N2), of the 2018/2019 seasonal influenza. No mixed infection A (H1N1) pdm09 and A (H3N2) has been demonstrated. The virus was named A / Denmark / 3176/2019 (see here more information about the influenza vaccine nomenclature ).

The Statens Serum Institute estimates that the subsequent risk of transmission of this virus is weak.
(Continue . . . )

Sources: European Center for Disease Prevention and Control; World Health Organization ; Flu News Europe website.

While the current paucity of case detections suggests these hybrid H1N2 viruses don't transmit very well, it is worth noting this patient doesn't appear to have been co-infected with H1N1 and H3N2 at the time the samples were taken.
These H1N2 cases are worth our notice, but a far greater concern would be 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).
I would imagine we'll see more updates and analysis from the CDC and the ECDC on this latest case in the days to come.