New Delhi, Sep 24 : The former chair of the UK Vaccine Taskforce Kate Bingham has in a new book warned of a next pandemic that could come from a million unknown viruses and kill about 50 million people like the Spanish Flu. The excerpt of the book, co-authored with another vaccine boffin Tim Hames, published in the Daily Mail explains how the next pandemic might unfold and calls for pandemic preparedness. "The 1918-19 flu pandemic killed at least 50 million people worldwide, twice as many as were killed in World War I," they said. "Today, we could expect a similar death toll from one of the many viruses that already exist. There are more viruses busily replicating and mutating than all the other life forms on our planet combined. Not all of them pose a threat to humans, of course - but plenty do." According to the experts, thousands of different viruses could evolve to spark a pandemic. There is also a risk that viruses could jump between species and "mutate dramatically". "So far, scientists are aware of 25 virus families, each of them comprising hundreds or thousands of different viruses, any of which could evolve to cause a pandemic," Bingham and Hames said. In May, the World Health Organization (WHO) also warned of the threat of an 'inevitable' next pandemic 'Disease X, raising concerns across the globe. Disease X was first coined in 2018 by the WHO, a year before the Covid-19 pandemic struck the world. It is among the WHO's 'Blue print list priority diseases' that could cause the next deadly pandemic and includes Ebola, SARS and Zika. 'Disease X represents the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease,' the WHO said. The Blueprint list highlights infectious diseases for which we lack medical countermeasures. Some public health experts believe the next Disease X will be zoonotic, meaning it will originate in wild or domestic animals, then spill over to infect humans, as Ebola, HIV/AIDS and Covid-19. Although the Covid-19 pandemic killed some 20 million people globally, the experts contended that the world got somewhat "lucky". "The point is that the vast majority of people infected with the virus managed to recover," the experts said. "Ebola, on the other hand, has a fatality rate of around 67 per cent. Bird flu is not far behind at 60 per cent. Even MERS hit 34 per cent. So we certainly can't bank on the next pandemic being easily contained." /IANS