Right Arm or Left Arm? How Does the Efficacy of Vaccines Depend on Which Arm It Was Injected In?

What is the first thing you think about when you go in for an injection? Apart from regretting their actions that landed them in this place, people usually think about whether the needles are clean or not, whether the professional who is going to violate you knows what they are doing, and similar thoughts.

But have you ever, in your sweet life, thought which hand is better for you to get injected? I bet not! Not unless one of your hands is injured. But why so? Well, if that’s the question you’ve been plagued by today, then you’re in luck!

Well, it isn’t complicated. You visit the doctor, who pulls up your sleeve and vaccinates you on any arm of their choosing. Right? Well, it isn’t so simple.

Researchers from Germany believe that the side matters when it comes to vaccinations and boosters. Their evidence also suggests that for the COVID-19 vaccine, you need to pick the same arm where the initial dose was administered.

For many people, this is subjective and is decided way before they reach the doctor’s clinic. Most of the time, they choose the same side because they have to use their non-dominant arm. The German study might be trying to teach us something - that the inclination might have benefits that transcend protecting the dominant hand.

One study shows that the same arm vaccination is better than a different arm vaccination. What difference does it make? None, to be honest.

To sum up, is there any evidence to choose one method of vaccination over the other? So let us instead dive into how our bodies combat germs, the roles our arms play and whether it is prudent to extend the same one every time the doctor gets a needle ready. But before we proceed, we must learn a little something about immunisation.

Immunisation means making a person resistant to a particular disease, usually through the administration of a vaccine. It involves stimulating the body’s immune response to come up with antibodies that safeguard against future infections or diseases.

Because of this, the individual receiving the vaccine gets safeguarded, yes, but it also results in something more important - community-wide protection, also known as herd immunity. When a major part of the population gets immunised, the spread of contagion gets contained, so as to speak.

Indirect protection is also extended to people who haven’t gotten vaccinated, like infants or people with compromised immune systems. There ain’t nothing safer than a modern vaccine, one of the most powerful tools in public health.

High immunisation rates make sure that societies can prevent outbreaks, bring down healthcare burdens and keep future generations safe, from once-devastating outbreaks.

When the first dose of a vaccine, also known as the primary dose, enters your body, it initiates the process of building immunity against a particular germ or disease.

What it does is, introduce your immune system to a harmless version of the germ - inactivated or weakened, so the body can recognise it and fight it. The primary dose is quintessential for triggering this immune response. However, the protection it provides is scant.

That’s when the booster dose comes in. You see, as time goes by the initial immune response might weaken as antibody levels decrease. The booster dose doesn’t allow that to happen.

The deltoid is the preferred destination for vaccines because muscles are good at absorbing antigens. There’s more blood here, so it's better for the vaccine itself.

Probably. There’s very little data suggesting otherwise. One small, recent study of COVID vaccines in adults found that both the same-arm and different-arm vaccines elicited a strong immune response. The same arm group gave rise to robust antibodies as well as higher levels of the specialised immune cells that destroy infected cells. One study was all for the same arm vaxxing. There’s no evidence to bolster a recommendation.

Okay - there are a lot of folks who have been long since exposed to the SARS-CoV-2 virus, a number of times, either through vaccination or infection or both.

While recent studies shed light on vaccination against COVID-19, researchers claim that they expect the improved immune response to be constant for other multi-dose vaccines.

Further research is the norm - to find out whether contralateral vaxxing boosts immune response for other vaccines and also among children.

Till they decide, however, whether the right arm is better or the left one is, do extend the arm of your choice whenever your doctor asks, unless they themselves tell you otherwise.

To sum up, there’s no hard and fast rule about which arm you should get inoculated in. According to recent research, sticking to the same arm for follow-up doses, especially for vaccines like COVID-19, would slightly increase your immune response by stimulating the same group of lymph nodes.

For most people, however, the choice boils down to comfort and convenience. If you’re right-handed, you might want to get poked in the left arm to avoid post-shooting soreness messing with your daily tasks. Whichever arm you choose, what matters is getting the damn vaccine so you stay protected, as does your community.

Q. Does it matter which arm I am getting a vaccine in?

A. There’s no rule as such. Having said that, stick to your same arm for follow up doses, that could increase your immune response by stimulating the same group of lymph nodes. To sum up, choose whatever you’re comfortable with. It doesn’t matter.

Q. Can I get the vaccine in my behind?

A. You aren’t a child, so no getting vaccines in the bum. Stick to the arm, and don’t embarrass yourself or your doctor.

Q. Can I get the booster dose in the other arm?

A. It is better to extend the same arm where you got your initial dose for your booster dose.

Q. Will switching arms between doses affect how sore I feel afterwards ?

A. Yes, potentially. Some people report soreness or discomfort at the injection site that can last for a day or two. If you're worried about pain affecting your dominant arm, opt for the non-dominant arm.

Q. Why does the immune response change depending on the arm used?

A. The immune system responds locally at first—lymph nodes near the injection site are the first to react. Reusing the same arm may re-engage the same group of lymph nodes, potentially leading to better immunity.