A new strain of swine flu with "pandemic potential" has been identified by scientists in China, according to a newly-released study.
Researchers from the China Agricultural University, the Chinese Centre for Disease Control and Prevention and the University of Nottingham, in the UK, revealed that influenza virus surveillance on pigs between 2011 and 2018 has led to the discovery of a new H1N1 strain they have named G4.
"G4 viruses have all the essential hallmarks of a candidate pandemic virus," the study, released on Monday in the PNAS journal, states.
"Of concern is that swine workers show elevated seroprevalence for G4 virus. Controlling the prevailing G4 EA H1N1 viruses in pigs and close monitoring in human populations, especially the workers in swine industry, should be urgently implemented," it adds.
The virus is for now transmitted from pigs to humans with little evidence of human to human transmission but researchers stressed that the virus has "acquired increased human infectivity".
Serological surveillance carried out on 338 swine workers found that 10.4 per cent were positive to the G4 EA H1N1 virus. The rate increased to 20.5 per cent in participants between the ages of 18 to 35.
"Such infectivity greatly enhances the opportunity for virus adaptation in humans and raises concerns for the possible generation of pandemic viruses," researchers said.
They also found that human influenza vaccine strains do not provide immunity against G4 viruses.
The 2009 outbreak of a new strain of swine flu killed between 157,000 and 575,000 people worldwide, according to the US Centers for Disease Control and Prevention (CDC).
Eighty per cent of the fatalities were estimated to have occurred in people younger than 65 years of age. Nearly one-third of people over the age of 60 had antibodies against the virus, "likely from exposure to an older H1N1 virus earlier in their lives," the CDC said.
A vaccine was quickly developed and the pandemic was declared over by the World Health Organization in August 2010.