Bird flu has spread to cows and is spreading rapidly through herds in the United States, causing scientists to worry. Just four years since the start of Covid, the unprecedented spread of a new strain of H5N1, or bird flu, among US dairy cows is a reminder of our vulnerability to new viral threats. Jeremy Farrar, the World Health Organization's (WHO) chief scientist, said last week that the risk of the new strain being transmitted to humans was a "major concern". Bird flu rarely infects humans, but is often fatal when it does. According to the WHO, the human mortality rate since 2003 is 52 percent. The fact that the virus appeared in mammals such as cows suggests that the virus has mutated and brings it one step closer to infecting humans. For decades, bird flu was considered a pandemic threat, but, as the name suggests, it mostly affected birds. "This news confirms the flu's ability to surprise us," Paul Digard, professor of virology and flu specialist at the University of Edinburgh, told Politico. "Historically, we have considered cows to be at very low risk for influenza A (a subtype of influenza that causes disease in humans and includes the virus that is now spreading to cows). The threat assessment has been raised by one level," Digard added. How widespread is the new strain? It is probably more widespread than previously reported. "I believe the spread of the disease will be far greater than the number of farms that have been reported," said James Wood, head of the department of veterinary medicine at Cambridge. The discovery of viral RNA in milk indicates that the disease is more widespread than previously thought, Wood explained. As of Thursday in the US, about one in five retail milk samples tested positive for virus fragments. Is the milk safe to consume? Viral particles have been detected in commercial milk in the US, but that doesn't necessarily mean it's unsafe to drink. Pasteurization is effective at killing the flu, and US authorities have said there is no evidence that the RNA particles detected in the milk could infect anyone. US federal agencies (USDA, USFDA, CDC) reiterated that "the commercial milk supply is safe." They also add that pasteurization is "likely" to inactivate avian influenza virus in milk and acknowledge that "no study on the effects of pasteurization on highly pathogenic avian influenza viruses such as H5N1 in cow's milk has been completed before." The detection of viral RNA in American milk is probably not a major concern for Europe. US milk imports to the EU are "very close to zero" and "statistically insignificant in terms of trade," an EU official told Politico. What is the risk to humans? So far, the risk to humans is limited, but there's a lot we don't know about the species since it's so new. At least one human case of the new strain has been reported, but there is no evidence of human-to-human transmission, a key indicator of a pandemic threat. The risk is that the virus mutates further and eventually develops the ability to infect humans more easily. The more widespread the virus is among animals, the more opportunity it has to do this. Has a new species been discovered in Europe? At the moment, the EU countries are closely following the developments. "Infections in dairy cows in the US are with the H5N1 strain that has not been detected in Europe. We are closely monitoring the situation and its possible development," a spokesperson for the European Food Safety Agency (EFSA) told Politico. The European Commission spokesman added that it carefully monitors any genetic evolution of the virus, but that the threat to human health is still low for the general public. EFSA advises increased surveillance of mammals, especially those near poultry facilities infected with avian influenza. Do we have a bird flu vaccine? There are vaccines that may work against bird flu, but it's still unclear how effective they would be against a particular strain and how quickly companies can ramp up production. A GSK spokesperson told Politico that the company has a contract with the EU's health emergency preparedness and response body to produce 85 million doses of the pandemic preparedness vaccine, Adjupanrix, if needed. Adjupanrix is ​​a "mock-up" flu vaccine that can be adapted to any type of flu that occurs as a pandemic. A spokesman for the European Commission, meanwhile, confirmed it has a joint contract with GSK and CSL Seqirus to supply personalized flu vaccines if needed in a pandemic. Andrew Fenwick, a spokesman for CSL Seqirus, told Politico that the company's zoonotic flu vaccine is likely to protect against the strain currently circulating in the US.