The EU's drug watchdog on Wednesday approved an updated version of Pfizer and BioNTech's anti-Covid jab to counter an infectious subvariant of the virus as winter approaches.

The World Health Organisation in May said it no longer considered Covid-19 a global health emergency, but the virus is still circulating -- and new variants are being tracked.

The European Medicines Agency said it "has recommended authorising an adapted Comirnaty vaccine targeting the Omicron XBB.1.5 subvariant".

The EMA in June recommended that vaccines be updated to target the XBB strain of the virus which have become dominant in Europe and other parts of the world.

Known as Comirnaty Omicron XBB.1.5, the mRNA vaccine is to be used to prevent Covid-19 in adults and children from six months.

Adults and children over five require a single shot "irrespective of their Covid-19 vaccination history" while younger children may get "one or three doses depending on whether they have completed a primary vaccination course or have had Covid-19" the Amsterdam-based EMA said.

Comirnaty uses messenger RNA technology which carries instructions how to make the spike protein which the virus uses to enter the body's cells.

When a person is given the vaccine, some of their cells will read the mRNA instructions and temporarily produce the spike protein.

If the vaccinated person later comes into contact with the virus, the immune system will recognise the spike protein on its surface and be prepared to attack it.

Comirnaty was first authorised in the EU in September 2020 with versions targeting other Covid-19 subvariants, in September 2022.

"Side effects are typically mild and short-lived," the EMA said, but added "that more serious side effects may rarely occur."

Pharmaceutical firms Moderna and Novavax and others are working on updating their Covid vaccines to target XBB subvariants.

The WHO is currently monitoring upwards of 10 variants and their descent lineages.