A new study from the Garvan and Kirby Institutes in Sydney has looked at whether it makes a difference which arm gets your booster shot i.e. subsequent vaccinations to the first one.
It turns out the immune response is much more effective if the second shot is given into the same arm.
The researchers studied mice then verified their findings in humans and published in the prestigious journal Cell.
What appears to happen is that after the first immunisation, macrophages (see How safe are tattoos – really? story) gather in the local lymph nodes carrying the history of the vaccine with them and pass on the immune message to special memory cells which line up at the surface of that node. When the second immunisation is given, the macrophages are ready for action – primed to respond to the vaccine from the previous dose. They then pass on the message to the memory white blood cells which then throw the switch to producing the antibodies to whatever virus the vaccine is designed to combat.
The trial in humans was done using the COVID-19 vaccine. The main difference was the speed of antibody production. In the end it didn’t matter which arm was injected because eventually the antibody levels were the same. However, the response was much faster in the same arm group. This matters when there’s a lot of viruses around as is the case with both COVID and flu or if you’re in the middle of an outbreak.
It’s usually not too difficult to remember which arm you were jabbed in last. Most of us have vaccinations in our non-dominant arm (left arm for right handers and vice versa).
