Wednesday, December 1, 2021

Why COVID-19 Vaccine Doses Differ by Age

People are born quite helpless and they need to develop a lot. And just like you must learn to walk, your immune system must learn to defend itself against infections. Over time, your immune system matures at different stages, much like you transitioned from crawling to standing, walking and running.

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

I am an immunologist, and this is how I explain to my pediatric and adult patients how vaccines work in people of all ages.

Two halves of the immune system

The maturation process of immunity begins shortly after birth.

When you are born, your main immune defenses are provided by antibodies that your mother passes through the placenta and breast milk. They provide so-called passive immunity. The newborn’s adaptive immune system – the part of your immune system that will make your own antibodies – isn’t working yet. The process begins immediately, but it can take years for the adaptive immune system to reach full maturity.

Fortunately, you were also born with a so-called innate immune system – and it persists throughout your life. You don’t have to study to fight infections and promote health, as the adaptive immune system does. Without an innate immune system, people would get sick much faster and more often.

READ MORE:First children receive COVID-19 vaccine as part of nationwide rollout

The innate immune system starts in your skin and mucous membranes. If any microbes overcome these physical obstacles, they have enzymes just waiting to destroy foreign organisms. In addition, there are specialized cells that seek everything but you to kill intruders, while other cells called phagocytes gobble up the invaders.

So, the innate immune system is your body’s first reaction. This gives you a little time. Then your adaptive immune system goes into action.

When you receive a vaccine through a vaccine or infection, your adaptive immune system begins to actively make its own antibodies. These are proteins that act as suckers and stick to viruses or bacteria to help the body get rid of germs faster and prevent the spread of infection. Antibodies specialize in recognizing and eliminating a specific attacker.

The adaptive immune system can learn about a new infection or remember one that it hasn’t encountered in a long time.

Vaccines affect the development of the immune system

Just like a baby learns to walk, even if you don’t protect stairs and pools for it, your immune system can learn to suppress an invading virus without a vaccine – but the likelihood of injury is much higher.

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Vaccines work by causing the formation of antibodies that recognize a particular microbe and work to counteract it safer than getting infected the first time without it. How well a vaccine works depends on how many antibodies you make in response to it, how effective they are, and how safe the vaccine is.

When researchers work to fine tune the dosage of a vaccine for different age groups, they need to know which parts of the immune system are working and which parts are not fully active in humans at every stage of development. This is one of the reasons why some vaccines – such as COVID-19 – are being tested and approved on different schedules for adults, teens, children and babies.

Some infant vaccines are given in batches, which means they are given the same vaccine multiple times over several months. A child’s adaptive immune system at this age is prone to forgetfulness or inattention – just like a child stumbles while trying to get up and walk. With each exposure, every aspect of the immune system becomes stronger and better protects against potential infection.

Some vaccines need to be given multiple times. CDC National Center for Immunization and Respiratory Diseases, CC BY

After 4 years and throughout your younger adulthood, your immune system becomes more responsive and less prone to forgetting. It is no coincidence that it is during this period that people most often suffer from allergies. Regarding the Pfizer COVID-19 vaccine, the researchers found that children ages 5 to 11 had a similar immune response and safety response at the level of one-third of the dose used for children ages 12 and older.

Scientists usually begin researching vaccines with patients between the ages of 18 and 55. Their adult immune systems have matured and can be relied upon to report any adverse reactions reliably. Watching what happens in the adult age group also helps doctors predict what might happen when the vaccine is given to other people, and monitor for these side effects in younger age groups.

Around the age of 55, the adaptive immune system begins to become weaker and forgetful again, which in some ways is more like the developing system of an infant. Fortunately, vaccine boosters can quickly refresh the health of these elderly patients – for example, help protect them from accidental falls after they have learned to walk and run all their lives.

After all, vaccines provide the safest environment for training the immune system, and adjusting dosages for different age groups helps to ensure that each patient gets exactly what they need to get the job done.

This article is reprinted from The Conversation under a Creative Commons license. Read the original article.

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