One simple change could dramatically boost the impact of COVID-19 vaccines: ScienceAlert
Sometimes, the simplest solutions get lost in the chaos of scientific progress.
Since the advent of vaccines more than two centuries ago, researchers have studied all sorts of ways in which vaccination with weakened pathogens (or parts of them) can prepare the immune system for a full-blown attack — exploring different doses, vaccine agents, and forms. administration.
In all this time, very few experts have investigated the question: Does it matter which arm is vaccinated?
Researchers at Oregon Health & Science University (OHSU) suspect this may be the case.
It all started in the early days of the COVID-19 pandemic. Health care workers involved in studies on the immune response to new COVID-19 vaccines have been asking experts at Ohio State University whether they should switch arms between the first and second dose.
The team wasn’t sure what advice to give. Until then, most scientists assumed it didn’t matter.
“This question has not been widely studied, so we decided to investigate it,” says infectious disease specialist Marcel Kerlin.
When Kerlin and his colleagues combed the scientific literature, they could find only four papers on the topic. The results were mixed.
One randomized controlled trial among infants found that influenza vaccines given at 2, 3, and 4 months in different arms resulted in higher antibody levels than when given in the same arm.
However, a more recent study conducted in 2023 found higher immune responses after COVID-19 vaccines were given in the same arm rather than different arms.
To get a clearer picture, researchers at Ohio University tested the antibody levels of 947 participants who received two doses of a COVID-19 vaccine.
Half of the group was randomized to receive the second dose in the same arm as the first dose, while the other half received overlapping doses in different arms. Four weeks after the second dose, serum antibodies to SARS-CoV-2 were 1.4 times higher in those who received the vaccine in different arms.
A subgroup of 108 people were matched into 54 pairs based on their sex, age and time of vaccinations, and their blood work was compared.
Serum samples collected in the weeks and months following vaccination showed clear differences between the two groups. Four weeks after the second dose, those who received doses in both arms had up to a four-fold increase in SARS-CoV-2-specific serum antibodies compared with those who received doses in only one arm.
What’s more, this improved immune response lasted more than a year after the booster dose was given.
“This turns out to be one of the most important things we’ve discovered, and it’s probably not just for Covid vaccines,” Kerlin posits.
“We may be seeing an important immune function.”
Kerlin and his colleagues aren’t sure yet what this special function is, or how it works, but they have an idea.
When the vaccine is administered into the muscle, the antigens in the drug are recognized by immune cells, which “cuff” the invaders and take them to the lymph nodes for further interrogation. This then primes the immune system against that particular antigen by sending the required signals to the invaders.
The truth is that different sides of the body flow to different lymph nodes, so by stimulating the immune response on both sides, the body may be more careful.
“By switching the arms, the memory is formed in two locations instead of one,” Kerlin explains.
This is the opposite of what the 2023 study found. It suggested that vaccinations in the same arm better prepare the immune system for COVID-19. The reason for the difference in results may be due to the timing of blood tests.
A 2023 study tested blood serum just two weeks after vaccinations were given.
However, immune cells that retain antigen properties continue to grow and mature for several months after vaccination.
After just three weeks, researchers at Ohio University noticed that injections in both arms began to show better results than in the same arm, and these benefits gradually improved, reaching their peak in the fourth week and continuing for several months after that.
While more research is needed to understand the pros and cons of vaccinating different arms, Kerlin says he wouldn’t hesitate to switch it up with his next booster vaccine.
The study was published in Journal of Clinical Investigation.