Why do some vaccines last longer than others? - (10/26/2021)

By Dr. Ron Gasbarro 

Jake was in the pharmacy scouting for bargains when he said to the pharmacist, "Lots of talk about vaccines lately." The pharmacist peered over his glasses and nodded, hoping he would not get another anti-vaccine rant. "As a dad who has taken 3 kids to the doctor's office for dozens of vaccines over the years, I have to ask," said Jake. "Why do some vaccines last longer than others?"

The pharmacist explained that the object of vaccination is to instruct the immune system to recognize and protect the cells from infection, usually by a type of virus or bacteria. Once your cells can recognize the invading infectious agent, they form antibodies that act as suits of armor to shield the agent from attacking them. Hence, the cells have been immunized. In fact, the word immunization comes from the Latin word immunes, meaning "a group of soldiers who, once they fought and survived a battle, never had to fight again." Thus, immunity has come to mean freedom from anything troublesome. In the case of vaccines, our bodies are the hosts; infectious germs are the enemy; the vaccines are the soldiers, and the freedom gained is from disease.

And it is true, some vaccines are typically "one and done." That's because some infectious agents are genetically stable, which means that they do not change their shape or other characteristics throughout a person's life. Examples would be the measles and the chickenpox viruses, both very contagious agents. Measles provokes a highly robust immune response in the body. This response is so strong that one study revealed that a single exposure could produce antibodies for over 200 years. Chickenpox, caused by the varicella-zoster virus, regains its ability to infect the body after approximately 50 years. Consequently, a second case of chickenpox in an individual is rare. However, the body's immune response to this pox – that is, its ability to remember that this virus is the enemy – is not as vigorous as it is to measles. The poxvirus may lie dormant in our cells until we are older as our immune system weakens. At this point, it can reactivate with a vengeance called shingles (herpes zoster). One might regard the shingles vaccine as a booster for one's waning chickenpox immunity. 

The pharmacist told Jake that "Even though the immune system has a memory, its ability to recognize some invaders memory is not always perfect." He explained that some pathogens can mutate into slightly different shapes – or strains – which the immune system no longer recognizes. That is why booster shots are given. They can "reset" the immune system, replacing old memory cells with those directed solely at the agent's newer strain. 

Finally, as Jake knows very well, infants need a slew of shots in their first years. While a child inherits its mother's immunity to various diseases, that protection wanes after a few months. And the child's immune system has not yet developed sufficiently enough to ward off many, often life-threatening illnesses. The point is to keep immunizing children before they are exposed to these diseases, which they can catch anywhere from daycare to department stores. 

As for the COVID-19 vaccines, years may go by before we know how to tame that virus. It may be through boosters or via a new technology that will deliver complete, permanent immunity. "In the meantime," said the pharmacist, "Pay attention to those ‘wash-your-hands’ reminders and get whichever COVID vaccine you can. I've read that Canadians and Australians are more likely than Americans to value what benefits the greater good over what benefits individual rights. Getting vaccinated always benefits the greater good. The virus is blind to personal rights." 

Ron Gasbarro, PharmD, is a recovering pharmacist and writer-in-residence at Rx-Press.


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