Why vaccine doses differ for babies, children, teens, and adults – immunologist explains how your immune system changes as you get older

(The conversation) – Human beings are born quite helpless, with a lot of development to do. And just like you need to learn to walk, your immune system needs to learn to defend itself against infections. Over time, your immune system matures through different stages, much the same way you went from crawling to standing, walking and running.

This process is one of the reasons why scientists are studying the immune response to a vaccine in different age groups, and why, for example, COVID-19 vaccines need to be tested separately in children aged 5 to 11. and those aged 12 to 16. Doctors want to use the dose of vaccine that offers the best protection with the fewest side effects. And that will depend on how the immune system works as it develops – something you can’t really tell from the outside.

I am an immunologist, and here’s how I teach my pediatric and adult patients how vaccines work in people of all ages.

Two halves of the immune system

The immune maturation process begins shortly after birth.

At birth, your main immune protection comes from the antibodies your mother shared through the placenta and breast milk. They provide what is called passive immunity. Adaptive immune system of the newborn – the part of your immune system that will make your own antibodies – is not yet fully operational. The process starts right away, but it can take years for the adaptive immune system to fully mature.

Fortunately, you were also born with what is called the innate immune system – and it lasts your whole life. It doesn’t need to be learned to fight infections and promote health like the adaptive immune system does. Without the innate immune system, people would get sick much faster and more often.

The innate immune system begins with your skin and mucous membranes. If germs cross these physical barriers, it contains enzymes that are just waiting to break down foreign organisms. Beyond that, there are specialized cells looking for anything other than you in order to kill intruders, while other cells called phagocytes gobble up invaders.

The innate immune system is therefore your body’s first responder. It saves you a little time. Then your adaptive immune system kicks in and joins the fight.

When you are immune to a vaccine or infection, your adaptive immune system actively begins to make your own antibodies. These are proteins that act like suction cups and adhere to viruses or bacteria to help the body get rid of germs faster and prevent infection from spreading. Antibodies are specialized in recognizing and eliminating a particular intruder.

The adaptive immune system may learn about a new infection or remember an infection it has not seen for a long time.

Vaccines help immune development

In the same way that an infant will learn to walk even if you don’t secure the stairs and swimming pools for it, your immune system can learn to crush an invading virus without a vaccine – but the risk of injury is much greater.

Vaccines work by triggering the creation of antibodies that will recognize a specific germ and work to fight it more safely than getting the infection for the first time without it. The effectiveness of a vaccine is a combination of the number of antibodies you make in response, their effectiveness, and the safety of the vaccine.

When researchers work to refine the dosage of a vaccine for different age groups, they need to know which parts of the immune system are in-line and which parts are not fully active in people at each stage of development. This is part of the reason why some vaccines – as for COVID-19 – be tested and approved at different times for adults, adolescents, children and babies.

A number of vaccines for infants are given in series, which means that they are given the same type of vaccine several times over the course of a few months. A baby’s adaptive immune system tends to forget or not listen at this age, much like a baby falters when trying to stand and walk. With every exposure, every aspect of the immune system get stronger and better to defend against potential infection.

After 4 years and during younger adult life, your immune system tends to be more responsive and less prone to forgetfulness. It is no coincidence that this is when people tend to gain most of their allergies. For Pfizer’s COVID-19 vaccine, researchers found that children aged 5 to 11 had an immune and safety response similar to one third of the dose used for ages 12 and up.

Scientists tend to start with patients between the ages of 18 and 55 when studying vaccines. Their adult immune systems have matured and can be relied upon to reliably report any side effects. Seeing what is happening in the adult age group also helps doctors predict what might happen when a vaccine is given to others and be on the lookout for these side effects in age groups. younger.

Around age 55, the adaptive immune system starts to get weaker and forgetful, in some ways closer to the developing infant system. Fortunately, vaccine boosters can provide a quick reminder for these older patients, such as helping them protect them from accidental falls after a lifetime of mastering walking and running.

Ultimately, vaccines provide the safest environment for the immune system to learn, and adjusting dosages for different age groups helps ensure that each patient gets exactly what is needed to do the job.