Last year witnessed several outbreaks that underscore the reality of zoonotic influenza, revealing vulnerabilities across all age groups and highlighting the risks for individuals both with and without comorbidities. These outbreaks also emphasized the various exposures that can lead to swine influenza infection. Of particular interest is the meticulous analysis conducted by scientists, who trace the viruses’ evolutionary paths and categorize them within phylogenetic trees, shedding light on their relationships.
The diversity of zoonotic influenza viruses causing human infections in 2023 raised concerns, with some strains leading to severe disease and exhibiting a high mortality rate. While in 2023 these viruses did not readily transmit from person to person, the potential for future pandemics remains uncertain, necessitating sustained vigilance and preparedness.
The World Health Organization (WHO), in collaboration with its partners, remains dedicated to enhancing surveillance in both animal and human populations. Rigorous investigation of each zoonotic infection is underway, alongside efforts to fortify pandemic preparedness planning and improve readiness for future influenza pandemics.
Here’s a summary of notable swine influenza outbreaks reported to WHO in 2023:
Brazil:
In June 2023, WHO was notified of a fatal laboratory-confirmed human case of infection with a swine-origin influenza A(H1N1) variant virus in Paraná state. The patient, a 42-year-old woman with underlying medical conditions, resided near a swine farm. Although she had no direct contact with pigs, two of her close contacts, who worked at a swine farm, remained unaffected. Sporadic human cases of influenza A(H1N1)v have been previously reported in Brazil.
United States of America:
In August 2023, WHO received notification of a human infection with a novel influenza A(H1N2) variant virus in Michigan. The patient, under 18 years old with no comorbidities, had visited an agricultural fair where swine exposure occurred. This marked the first influenza A(H1N2)v virus infection identified in the United States in 2023.
The Netherlands:
In September 2023, a laboratory-confirmed human case of infection with a swine-origin influenza A(H1N1) variant virus was reported in North Brabant province. The affected adult, with no underlying medical conditions or occupational animal exposure, recovered without complications. This incident represented the first human infection caused by influenza A(H1N1)v virus reported in the Netherlands in 2023.
United Kingdom of Great Britain and Northern Ireland:
In November 2023, a human case of swine-origin influenza A(H1N2) virus infection was reported. The patient experienced mild symptoms and fully recovered without hospitalization. Investigation into the source of infection was ongoing, with proximity to pig farms noted despite no direct exposure reported.
These outbreaks underscore the importance of ongoing surveillance, prompt investigation, and collaboration in addressing the threat of zoonotic influenza.
