Influenza A(H1N2)v Virus in Humans

On 15 December 2020, the Brazil Ministry of Health reported the second confirmed human infection with influenza A(H1N2) variant virus, shortened to A(H1N2)v, in Brazil in 2020.

The case was a 4 year-old female who lives on a farm which also functions as a swine slaughter in Irati municipality, Paraná state. On 16 November 2020, the patient had an illness onset with a fever, cough, coryza, headache and dyspnea, and was provided ambulatory care on the same day at Darcy Vargas Hospital. She was treated with medication for fever and headache and has since recovered. No symptomatic contacts were found among the case’s family.

On 18 and 19 November, respiratory samples were collected for testing. The Parana State Laboratory detected an unsubtypeable influenza A virus and the samples were sent to the the National Influenza Centre (NIC) in Rio de Janeiro for complete viral genome sequencing, where influenza A(H1N2)v virus was confirmed on 14 December 2020.

This case is actually the third human infection of influenza A(H1N2)v virus reported in Brazil. The first case was detected in 2015[1] and the second, 22-year-old female, in April 2020. These two confirmed cases lived in rural areas with pig farming and one case worked in a pig slaughterhouse.

The A(H1N2)v virus is genetically different from other variant viruses previously detected in humans in Brazil in 2015 and in April 2020, based on preliminary genetic analysis. The preliminary analysis shows that all genes are most similar to those from currently circulating influenza A(H1N1)pdm09 viruses, except for neuraminidase which is most similar to those from influenza A(H3N2) viruses.

This novel virus is the result of a reassortment of three different Influenza viruses: H1N2 (hemagglutinin), H3N2 (neuraminidase), and H1N1 (remaining genes). At the moment the Influenza A(H1N2)v virus appears not to be very contagious and does not result in serious illness. But all that can change rapidly.

[1] Resende et al: Whole-Genome Characterization of a Novel Human Influenza A(H1N2) Virus Variant, Brazil in Emerging Infectious Diseases - 2017. See here.