Imma Perfetto
Cosmos science journalist
Choosing to receive a vaccine’s first dose and booster in the same arm, rather than in separate ones, generates more effective immune response more quickly, Australian scientists have found.
Experiments in mice revealed the key to this lies in the lymph node closest to the vaccination site, where the vaccine response is generated.
A clinical study in 30 volunteers who received the Pfizer-BioNTech COVID-19 mRNA vaccine confirmed that the animal results also apply to humans.
“Those who received both doses in the same arm produced neutralising antibodies against SARS-CoV-2 significantly faster – within the first week after the second dose,” says Alexandra Carey-Hoppé, PhD student from the Kirby Institute in Sydney, and co-first author of the new Cell study.
Dr Mee Ling Munier, study co-senior author and Vaccine Immunogenomics group leader at the Kirby Institute, adds that the antibodies from the same arm group were also more effective against variants like Delta and Omicron.
“By 4 weeks, both groups had similar antibody levels, but that early protection could be crucial during an outbreak,” says Munier.
But if you’ve had your COVID jabs in different arms, Munier assures there’s no need to worry.
“Our research shows that over time the difference in protection diminishes,” she says.
“But during a pandemic, those first weeks of protection could make an enormous difference at a population level. The same-arm strategy could help achieve herd immunity faster – particularly important for rapidly mutating viruses where speed of response matters.”
The researchers had previously discovered that memory B cells, which are crucial for generating antibody responses when infections return, linger in the lymph node closest to the injection site.
Through experiments in mice, they have now shown that specialised immune cells called macrophages also become “primed” in the lymph node following vaccination.
“Macrophages are known to gobble up pathogens and clear away dead cells, but our research suggests the ones in the lymph nodes closest to the injection site also play a central role in orchestrating an effective vaccine response the next time around,” says Dr Rama Dhenni, the study’s co-first author who undertook the research as part of his PhD research at the Garvan Institute of Medical Research, in Sydney.
When a booster was given in the same location, these primed macrophages were already on red alert to efficiently capture the vaccine antigen and activate memory B cells to make high quality antibodies.
The new insights could help to improve future vaccination strategies and offer a promising new direction for research to enhance the effectiveness of vaccines.
“If we can understand how to replicate or enhance the interactions between memory B cells and these macrophages, we may be able to design next-generation vaccines that require fewer boosters,” says Professor Tri Phan, Director of the Precision Immunology Program at the Garvan Institute of Medical Research and study co-senior author.
