Hello, I'm Ros Atkins. Each week on the BBC World Service, I look in depth at one of the biggest issues in the news.

This time, it's the Oxford AstraZeneca vaccine. This is the sound of the piazza San Marco in Venice in February last year.

Three weeks before Italy became the first country in the world to announce a nationwide lockdown and this is how the

square sounded on Wednesday night.

Completely empty.

It's third lockdown has begun and the pandemic is far from over.

This week I'm going to look at one of the great puzzles of how the virus is being

tackled. It has been called the game changer in the fight against coronavirus and is a major hope for

a return to a more normal way of life by spring.

The Oxford AstraZeneca vaccine was hailed as a game changer,

easy to use, easy to transport and cheap a vaccine for the whole world, not just the wealthiest

parts of it.

So why are we hearing headlines like this?

Tonight to 10, the EU's biggest nations have now joined the list of countries

suspending use of the Oxford AstraZeneca vaccine.

A small number of people out of the

number of people out of the millions who've had the vaccine have suffered blood clots.

These suspensions were announced despite the World Health Organization

insisting the vaccine can still be used.

And Sabine Strauss from the European Medicine's agency reiterated this on Thursday

after taking another look at the issue.

This vaccine is safe and effective in preventing COVID-19

...