Health Alert: Influenza A(H1N2) Variant Virus Infection In UK

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Influenza A(H1N2) Variant Virus Infection In UK

Influenza A(H1N2) Variant Virus Infection In UK – On 25 November 2023, the International Health Regulations National Focal Point (IHR NFP) of the United Kingdom of Great Britain and Northern Ireland (United Kingdom) notified the World Health Organization (WHO) of a human case of swine-origin influenza A(H1N2) virus infection.

This is the first swine influenza A(H1N2)v case reported in the United Kingdom. Human infections with swine-origin influenza viruses have been sporadically detected in the past in countries in the Americas, Asia, Australia and Europe. When a human is infected with a swine-origin influenza virus, the virus is referred to as a variant (or “v”) virus.

Most human cases result from exposure to swine influenza viruses through direct contact with infected swine or contaminated environments. Current evidence suggests that these swine-origin influenza viruses have limited ability for sustained transmission among humans. This case was identified as part of routine surveillance of respiratory illnesses.

The source of infection for this case is under investigation and contact tracing is in process. To date, no other confirmed cases associated with this event have been reported. WHO is in communication with national authorities to monitor the situation closely. Ongoing investigations are in place to identify the source of the infection and to characterize the risks of this influenza variant virus.

WHO assesses the risk of spread of swine-origin influenza viruses through humans and/or community-level spread among humans as low. However, because these viruses continue to be detected in swine populations worldwide, further human cases following direct or indirect contact with infected swine can be expected.

Current evidence suggests that these viruses have not acquired the ability to sustain transmission among humans. 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.

WHO Advice

People with any respiratory symptoms should continue to follow the existing guidance, seek healthcare and avoid contact with other people while symptoms persist, particularly if the people they are coming into contact with are elderly or have existing medical conditions.

Surveillance: 

  • This case does not change the current WHO recommendations on public health measures and seasonal influenza surveillance.
  • WHO does not advise special traveler screening at points of entry or restrictions concerning the current situation of influenza viruses at the human-animal interface.
  • 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.

Notification and investigation:  

  • All human infections caused by a novel influenza subtype are notifiable under the IHR (2005) and State Parties 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.
  • In the 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 a history of exposure to animals, travel, and contact tracing should be conducted. The epidemiologic investigation should include early identification of unusual respiratory events that could signal person-to-person transmission of the novel virus. Clinical samples collected from the time and place of the case should be tested and sent to a WHO Collaboration Centre for further characterization.

Prevention measures: 

  • General hygiene measures, such as regular hand washing before and after touching animals and avoiding contact with sick animals, should be adhered to.
  • 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. Influenza viruses that infect pigs are different from human influenza viruses. There is no vaccine for zoonotic influenza infection licensed for use in humans. However, some partners have developed candidate vaccine viruses for novel zoonotic influenza viruses with pandemic potential as part of pandemic preparedness activities.
  • Usually, influenza vaccines against human influenza viruses are generally not expected to protect people from influenza viruses that normally circulate in pigs. Although the seasonal influenza vaccine does not protect against swine viruses, WHO recommends seasonal influenza vaccination to avoid severe disease.
  • In health-care settings, syndromic screening of health and care workers, patients, and visitors for symptoms of respiratory infections is recommended, accompanied with capacity and resources to implement transmission-based precautions to reduce the risk of health care-associated infections. If a case of a novel acute respiratory infection is suspected, please refer to advice in the WHO guideline for infection prevention and control of epidemic-and pandemic prone acute respiratory infections in health care.

WHO does not recommend any travel and/or trade restrictions for the United Kingdom based on the currently available information.