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

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

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.

Other current variants of concern also include:

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.

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.

The variants of concern have all undergone changes to their spike protein - the part of the virus which attaches to human cells.

Delta has some potentially important ones (such as L452R) that might make it spread more easily.

There is no evidence to indicate it causes more severe disease or might make current vaccines less effective, say UK officials.

One mutation, called N501Y, shared by the Alpha, Gamma and Beta, seems to make the virus better at infecting cells and spreading.

Experts have found a small number of cases of Alpha with this change too.

Current vaccines were designed for earlier versions of coronavirus, which means they may not be the ideal match for new variants and so might not work quite as well.

But experts say they are still very effective at protecting lives by cutting the risk of severe illness:

Doctors say it is vital that people get both doses to gain maximum protection against existing and emerging variants.

Experts are confident existing vaccines can be redesigned to better tackle emerging mutations.

Depending on how variants continue to develop, these could potentially be used to offer a booster vaccine to older or clinically vulnerable people later in the year.