The Guardian view on long Covid: an unknown enemy | Editorial

At least 2 million people in the UK are struggling with symptoms months or years after falling ill. They need support as well as treatment

How do you tackle a problem when you don't know what it is? Covid-19 was an unknown enemy, but was quickly identified. Long Covid, its equally unwelcome offspring, is a lesser threat, but is proving harder to pin down. Doctors are clear that it is widespread - yet are not sure how common it is, or how to respond.

This is in part because it is an umbrella term for a wide range of symptoms; the World Health Organization says that up to 200 have been recorded, with shortness of breath, brain fog and fatigue the most common, while others range from loss of smell and tinnitus to stomach aches and depression. It may be that five or six separate syndromes are involved. Most of the symptoms have numerous potential non-Covid causes, making it still harder to isolate which are related to the infection.