AUSTRALIAN researchers have revealed why receiving a booster vaccine in the same arm as the first dose can generate a more effective immune response more quickly.
The study, led by the Garvan Institute of Medical Research and the Kirby Institute at UNSW, and published in Cell, offers new insight that could help improve future vaccination strategies.
Until only recently, it was thought that when giving booster shots it did not matter which arm was used - that is, whether it was the same arm as the initial shot or the opposite arm.
However, German research published in 2023 found that when using the same arm for the booster, the immune response was greater than when given in the other arm.
The authors of that study speculated that the differences in immunogenicity could be due to action in the nearby lymph nodes, with limited involvement of lymph nodes on the other side.
That theory was borne out by the Australian researchers, who found that when a vaccine is administered, specialised immune cells called macrophages became 'primed' inside lymph nodes.
These macrophages then direct the positioning of memory B cells - immune cells that have a "memory" of specific antigens they encountered during a previous infection or vaccination - to more effectively respond to the booster when given in the same arm.
The findings, made in mice and validated in human participants, provide evidence to refine vaccination approaches and offer a promising new approach for enhancing vaccine effectiveness.
"This is a fundamental discovery in how the immune system organises itself to respond better to external threats - nature has come up with this brilliant system and we're just now beginning to understand it," said Professor Tri Phan, Director of the Precision Immunology Program at Garvan and co-senior author.
The researchers conducted a clinical study with 30 volunteers receiving the Pfizer-BioNTech COVID vaccine.
Twenty participants received their booster dose in the same arm as their first dose, while 10 had their second shot in the opposite arm.
Those who received both doses in the same arm produced neutralising antibodies against COVID significantly faster - within the first week after the second dose.
The antibodies from the same arm group were also more effective against COVID variants like Delta and Omicron.
"By four weeks, both groups had similar antibody levels, but that early protection could be crucial during an outbreak," said Dr Mee Ling Munier, co-senior author from the Kirby Institute, adding that when viruses are rapidly mutating, those first few weeks of protection "can make an important difference at a population level".
Read the paper HERE. KB
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