Influenza A(H1N2) variant virus – Brazil

Disease Outbreak News
4 January 2021

On 15 December 2020, the Brazil Ministry of Health reported the second confirmed human infection with influenza A(H1N2) variant virus [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, Paran? state. On 16 November 2020, the case had illness onset with a fever, cough, coryza, headache and dyspnea, and was provided ambulatory care on the same day at Darcy Vargas Hospital. He was treated with medication for fever and headache and has 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 Oswaldo Cruz Institute (Fiocruz), 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.

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 conducted by Fiocruz NIC. 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. Further characterization of the virus is underway. All influenza type A viruses detected by sentinel surveillance and viruses submitted from non-sentinel sites (hospital and peripheral laboratories) in Brazil are subtyped by properties of hemagglutinin (H) and neuraminidase (N) surface proteins. To date, no other human infections with variant viruses have been reported in Brazil.

This case is the third human infection of influenza A(H1N2)v virus reported in Parana state and in Brazil. The first case was detected in 2015 and the second in April 2020. These two confirmed cases lived in rural areas with pig farming and one case worked in a pig slaughterhouse.
Public health response

Local authorities carried out epidemiological and veterinary investigations to obtain more information about possible exposure, potential suspected cases, clinical features and evolution of the case among other epidemiological, virological and clinical information. While investigations are ongoing, local authorities enhanced laboratory surveillance and subtyping of influenza samples in Irati municipality where the case was reported.
WHO risk assessment

There has been some limited, non-sustained human-to-human transmission of variant influenza viruses, although ongoing community transmission has not been identified. Current evidence suggests that these viruses have not acquired the ability of sustained transmission among humans. The risk assessment will be reviewed if needed should further epidemiological or virological information become available.

Swine influenza viruses circulate in swine populations in many regions of the world. Depending on the geographic location, genetic characteristics of these viruses vary. When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a “variant influenza virus”. Most human cases are the result of exposure to swine influenza viruses through contact with infected swine or in some cases, contaminated environments. Further human cases can be expected because these viruses continue to be detected in swine populations around the world.

Influenza viruses which infect swine may be different from human influenza viruses. Thus, influenza vaccines against human influenza viruses are generally not expected to protect people from influenza viruses that normally circulate in pigs. In addition, pigs are susceptible to avian, human and swine influenza viruses; they potentially may be infected with influenza viruses from different species at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new virus. This type of major change in the influenza A viruses is known as antigenic shift. If this new virus causes illness in people and can be transmitted easily from person-to-person, an influenza pandemic can occur.

Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses that may affect human or animal health and timely virus sharing for risk assessment.

All human infections caused by a novel influenza subtype are notifiable under the International Health Regulations [IHR (2005)] and State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic. Evidence of illness is not required for this report.
WHO advice

This case does not change the current WHO recommendations on public health measures and surveillance of seasonal influenza.

WHO does not advise special traveler screening at points of entry or restrictions with regard to the current situation of influenza viruses at the human-animal interface.

Travelers to countries with known outbreaks of animal influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered or contact with any surfaces that appear to be contaminated with animal feces. Travelers should also wash their hands often with soap and water. Travelers should follow good food safety and good food hygiene practices. Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.

In case of a confirmed or suspected human infection caused by a novel influenza virus with pandemic potential, including a variant virus, a thorough epidemiologic investigation of history of exposure to animals, of travel, and contact tracing should be conducted, even while awaiting the confirmatory laboratory results. Epidemiologic investigations should include early identification of unusual respiratory events that could signal human-to-human transmission. Clinical samples collected from the time and place that the case occurred should be tested and sent to a WHO Collaboration Center for influenza for further characterization.

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