In two of these vaccines the viral particles used are not live.

At around 8 hours the cell is effectively dead and lyses to release the viral particles.

Instead, it has to trick the cell into providing the materials for making new viral particles.

Now there are millions of new viral particles that can go out and attack new cells.

It takes your immune system about 7-10 days to round up all the viral particles and get rid of them.

Eventual release of the viral particles is cytolytic and results in cell death.

"It thus reduces the viral particles considerably in the bloodstream," he said.

T4 has a burst size of approximately 100-150 viral particles per infected host.

It's thought to be caused by a viral particle called a prion.

Each green (positive) cell was counted as one viral particle.