CDC confirms fourth human case of infection with 50 percent mortality rate as fears rise over new pandemic

As with the previous cases, the patient is a dairy farm worker who came into contact with cows that tested positive for the H5N1 strain of bird flu, or avian influenza.

The person reported eye symptoms only, received oseltamivir - an anti-viral treatment - and has recovered, the CDC reports.

Asleep at the wheel?

The latest confirmed infection has not prompted the CDC to change its current H5N1 bird flu human health risk assessment for the US general public, which the agency considers to be low.

Others are less sanguine. Since the first mammal-to-human spread of the virus was confirmed back in April, health officials have raised concerns that the world is hurtling towards a pandemic far worse than Covid.

This fear was crystallised in June after it was confirmed that a 59-year-old man in Mexico died with a strain of the bird flu - H5N2. This was the first ever recorded death linked to this type of bird flu but history sets some worrying precedents.

Between January 2003 and March 28, 2024, WHO reported 888 human cases of bird flu infection, and 52 pecent were fatal, according to the organization’s latest report.

Thankfully, there have been no confirmed cases of human-to-human transmission.

But most infectious diseases are caused by viruses circulating in animals at first, and when these cross over into humans – a process known as zoonosis – they can cause disease outbreaks, epidemics and pandemics such as Ebola, flu or Covid-19.

According to the CDC, the spread of the virus among cows is a sign that it could mutate in them, potentially making it easier for the virus to spread to other animals and make the leap to humans.

Should it make the jump to humans, the death rate could be far higher than that seen during the height of the Covid pandemic.

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Robert Redfield, the former director of the US Centers for Disease Control and Prevention (CDC), puts the mortality rate from bird flu, at “somewhere between 25 and 50 percent".

In contrast, Covid-19 had a mortality rate of 0.6 percent.

Redfield's prediction may be an overestimate, reckons Yale Medicine infectious diseases specialist Scott Roberts, adding that there may be cases where people have no symptoms, are only mildly symptomatic, or haven’t sought care for their symptoms.

He also noted that if the virus did spread in humans, the percentage might be significantly lower if preventive approaches, including a vaccine, and treatments were made widely available.