When 100 passengers on a flight from Dubai to New York in September 2018 fell ill with respiratory symptoms, health officials were concerned that they might be carrying a serious respiratory illness called MERS-CoV (Middle East respiratory syndrome coronavirus) and quarantined the plane until further health checks could be completed.
Influenza may not always be thought of by most people as a serious illness – the symptoms of headaches, runny nose, cough and muscle pain can make people confuse it with a heavy cold. Yet seasonal influenza kills up to 650,000 people every year. That is why influenza vaccinations are so important, especially to protect young children, older people, pregnant women, or people who have vulnerable immune systems.
What most of us think of as 'the flu' is seasonal influenza, so called because it comes around in the coldest season twice a year in temperate zones of the world, and circulates year-round in the tropics and subtropics.
The influenza virus is constantly mutating – essentially putting on ever-changing disguises – to evade our immune systems. When a new virus emerges that can easily infect people and be spread between people, and to which most people have no immunity, it can turn into a pandemic. "Another pandemic caused by a new influenza virus is a certainty. But we do not know when it will happen, what virus strain it will be and how severe the disease will be,” said Dr Wenqing Zhang, the manager of World Health Organisation's Global Influenza Programme.