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What are the Delta, Gamma, Beta and Alpha Covid variants?

An outbreak of cases of SLOTXO the Delta variant of Covid is causing concern in China.

More than 300 cases have been spotted in 10 days - leading to increased testing and travel restrictions.

What is the Delta variant?

There are thousands of different types - or variants - of Covid circulating across the world. One of them, known as Delta or B.1.617.2, appears to be spreading quickly in many countries including the UK, where it has become the dominant variant.

The UK classes Delta as a "variant of concern" - these are kept under the closest watch by health officials.

Other current variants of concern also include:

• Alpha (B.1.1.7), first identified in the UK but which spread to more than 50 countries
• Beta (B.1.351), first identified in South Africa but which has been detected in at least 20 other countries, including the UK
• Gamma (P.1), first identified in Brazil but which has spread to more than 10 other countries, including the UK

Viruses mutate all the time and most changes are inconsequential. Some even harm the virus. But others can make the disease more infectious or threatening - and these mutations tend to dominate.

Is Delta more dangerous?

There is no evidence that Delta - or any of the other variants - cause more serious illness for the vast majority of people.

As with the original version, the risk remains highest for people who are elderly or have significant underlying health conditions.

But even so, if a variant is more infectious it will lead to more deaths in an unvaccinated population.

Vaccines offer high protection against severe illness with Covid-19, including infections caused by variants of concern. The shots also reduce the risk of infection. But they are not perfect and do not completely eliminate all risk.

It is unclear how many people in China are fully vaccinated, although authorities say more than 1.6 billion doses have been administered so far.

The advice to avoid infection remains the same for all strains: wash your hands, keep your distance, wear a face covering and be vigilant about ventilation.