Immunologist, Liezl Heyman, helps us understand what vaccines are and how they work.
Immunologic memory
We all have something called long-term immunologic memory. This is our ability to have a faster and more effective immune response to something harmful to our health (pathogens), such as viruses, that was encountered in the distant past.
Most infections are cleared by our immune system, sometimes without us even realising it, developing immunologic memory. This means our bodies activate white blood cells (lymphocytes) and antibodies to fight a specific virus should it ever enter our bodies again. When we encounter this virus or pathogen again, these lymphocytes kill it faster and more effectively, making us less ill for a shorter time or even not ill at all.
At birth, we all inherit antibodies from our mothers so we use our mothers’ immunologic memory to survive infections. Around age six to 12 months, our own immune system starts developing and therefore early childhood is fraught with primary infections while our own immunologic memory develops.
This is where vaccines come in. Vaccination substitutes primary infection, by giving us a safer form of the virus, activating memory lymphocytes and antibodies that offer future protection when we encounter the real virus in all its dangerous glory, with very light or no symptoms.
Antibodies and lymphocytes activated by vaccines prevent viruses from binding onto targeted body cells, prevent the actions of toxins released by viruses, and stop viruses from replicating.
Types of vaccines
Live vaccines were discovered first, and are the most effective (vaccines against smallpox and polio). Live vaccines use organisms that are not virulent (replicate in healthy vaccine recipients but don’t cause disease). One way to do this is to use organisms that have evolved to grow in animals, such as the cowpox virus, that was used as a vaccine against smallpox.
Antibodies made by our bodies against live vaccines such as those for measles and mumps remain in our bodies for decades after vaccination. Other live vaccines use weakened human pathogens or viruses that are incapable of causing disease. This is done by growing the organism in special conditions in a laboratory.
Killed organisms are less effective than live vaccines but safer since they don’t replicate in the body. The influenza vaccine is available as a live virus but is more frequently given as a killed virus.
Subunit vaccines are components of pathogens or viruses prepared by destroying the dangerous organisms, purifying the subunit, and inactivating it so it won’t cause the disease. The problem with subunits is that they need what we call adjuvants (boosters) to work effectively. The antibody response subunit vaccines lasts only for a short time compared to live vaccines. For example, the antibody to tetanus only remains in our bodies for about 10 years after vaccination, so a booster is needed.
Vaccine schedules
Vaccine schedules tell us at what age, when and how a vaccine should be given. The rubella vaccine that prevents infections in the womb, causing deformities in unborn children, is given to girls at puberty.
Haemophilus causes severe pneumonia and meningitis in very young infants so vaccines are given at a very early age. HPV vaccines prevent sexual transmission of the strains of HPV causing cervical cancer so they are given to girls at puberty.
Vaccine schedules also vary in different parts of the world. Measles is a major cause of death in infants in the developing world so, the vaccine is given as early as possible. In the developed world, measles is rare and tends to affect school-age children, so the vaccine is given later.
Without vaccines, our world would be a much more dangerous place and we would have very little resistance against those enemies lurking around, too small for us to see with the naked eye. They are there to keep us and our loved ones safe, so come on…go get that booster.
MEET THE EXPERT – Liezl Heyman
Liezl Heyman is the case manager, accounts clerk and research data manager at the Medical Oncology Centre of Rosebank. She has a master’s degree in social work and recently completed her BSc Hons in immunology, making her an immunologist.
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