Dr Dan Layton, CSIRO immunologist said:
"Not all immune responses are created equal. Particularly, as we age we see a decline in our ability to mount a strong and lasting immune response. Given COVID-19 disproportionately impacts the elderly, it is critical that during our winter months they have the best protection possible.
"Boosting the immunity of those most at risk as we head into winter in the southern hemisphere will support immune responses to be at their peak, not in decline. This will reduce the disease burden in these populations should we see another spike in cases.
"For people with severe immunodeficiency, the ability for their immune system to generate a protective response to a vaccine is diminished. This can be due to several reasons including medical treatments such as those given for cancer, genetic immune disorders and prolonged illness.
"They are particularly vulnerable both because of low immune response to vaccines as well as a reduced ability to fight the virus naturally. Giving additional boosts in this instance will ensure the best chance of reduced disease."