UK’s premier health agency has raised the high probability of a pandemic-level bird flu outbreak after the virus jumped to cows and then humans, citing the level to four. The UK Health Security Agency (UKHSA) says: "There is high uncertainty regarding the trajectory of the outbreak and there is no apparent reduction in transmission in response to the biosecurity measures that have been introduced to date."

Officials say they are monitoring the spread and risk of the H1N1 flu virus in humans after four dairy workers in the US tested positive for the condition in a scary advancement that saw the virus jump from birds to cows, spread between them, and end up in humans.

According to experts, a virus needs to be able to infect humans easily and spread at a large scale – causing infections and fatalities to become a pandemic. However, till now there has been no evidence that bird flu can be transmitted among humans.

UKHSA however, says that the scale of the spread of bird flu in the US means that it could find more ways to mutate, which could enable H5N1 to transmit between humans. "The recent outbreak in US dairy cattle demonstrates that influenza A (H5N1) continues to infect new mammals and spread between them," Dr. Susan Hopkins, the UKHSA chief medical advisor, told The Sun.

“While the current risk to the UK population from influenza A(H5N1) virus remains very low, an outbreak of this kind can increase the opportunities the virus has to evolve to spread between people at some point in the future,” she added.

Bird flu's level four risk means the disease has experienced "sustained multiple multispecies outbreaks" and "increasing human zoonotic cases or limited person-to-person exposure", according to a report by the health ministry.

To reach level five, the virus would have to cause "human outbreaks (larger or without identified zoonotic links)" meaning it spreads between humans. And then, for level six, there will have to be a sustained transmission between humans.

Dr. Susan said the UKHSA would "continue to monitor the situation closely". “UKHSA has established preparations in place for detections of human cases of avian flu and stands ready to initiate an appropriate public health response should it be needed," said Dr. Susan.

According to the guidelines issued by authorities, people have been advised to stay at least two meters away from wild birds and snap all contact with pigeons, swans, and seagulls.

Since the rise in the number of infections in humans in the US, news reports say many countries are now working towards creating vaccination programmes for their citizens, as a measure of precaution.

Last year, health officials told The Sun that the UK was drawing up plans to stockpile vaccines in case of a bird flu pandemic in humans. Earlier this year, the World Health Organisation initiated a review of available influenza vaccines and confirmed that they would work against the H5N1 virus circulating in cattle.

In the US scientists have announced a universal vaccine that protects against every form of flu – including bird flu – to be available within the next five years.