Health scare for Pope Francis as he is unable to stand at Vatican speech

Fears for the health of Pope Francis have resurfaced after he was unable to stand at an official event, explaining that he was 'not feeling strong.' 
Addressing Vatican officials in a Christmas speech on Monday, Francis said he had the flu. He said:

'Dear brothers and sisters, Forgive me for not standing up as I speak to you, but for some days I've been suffering from flu and I am not feeling very strong. With your permission, I'll speak to you sitting down.'

The pope has been unsteady of his feet at times in recent months, stumbling several times in public. Last week he celebrated his 79th birthday.

In November as walked up the steps in the Basilica of St John Lateran in Rome he seemingly tripped on his robes, forcing nearby priests to grasp his arms and help him up the steps.
The same week he tripped as he walked up some steps in St Peter's Square, this time being brought to his hands and knees.