Question & Answer #5

Do people have to receive two doses and do they have to be the same type of COVID-19 vaccine for it to be effective?

Answer:

Yes, both Comirnaty (Pfizer) and Vaxzevria (AstraZeneca) require two doses to provide the best immunity. It is important you get the same type of COVID-19 vaccine. Evidence from clinical trials shows this is effective and is what is approved for use by the TGA.

When the immune system first encounters a vaccine, it activates 2 important types of white blood cells.

First up are the plasma B cells, which primarily focus on making antibodies against the pathogen (or germ that causes disease).

Unfortunately, this cell type is short-lived. Your body might be swimming in antibodies within just a few weeks. But without the second shot there is usually a rapid decline in antibodies against the pathogen.

Then there are the T cells, each of which identifies a particular pathogen to kill it.

Some of these memory T cells linger in the body for decades until they meet their target. This means immunity from vaccines or infections can sometimes last a lifetime. But you usually won't have many of this cell type until there is a second exposure to that pathogen, which happens through the booster dose. 

On second exposure to the same vaccine, the body can respond by creating a stronger immune response to fight the virus if required.

It is not yet known how long the COVID-19 vaccine protection will last. Clinical trials are currently happening to find out if we will need annual or longer booster doses to ensure long term immunity.

Information from: The Department of Health