Commentary: Childhood vaccinations are safe and effective

Imagine you are a parent of a healthy and active toddler. About a week ago, your child came down with what seemed to be a mild cold. Not really serious, it seemed. Just a runny nose and a low-grade fever, like the many other colds a small child endures in their first few years. But a few nights ago, your child developed a severe cough. And it has only gotten worse. He is suffering coughing bouts lasting continuously a minute or more, so intense that he cannot breathe. At the end of the bout, he sucks in air with a rattling whooping sound. The terror in his eyes almost kills you. And this is just getting worse. You bring him to the doctor, and he is diagnosed with pertussis, or whooping cough. And there is nothing the doctor can do. Two days later, you are planning a funeral for your darling little boy.

This is a nightmare that many parents endured a century ago. And here in the United States, it is now very rare. This is also true of a bunch of other childhood diseases, like measles, mumps, diptheria and typhoid fever. Diseases that were common and every parent's nightmare not very long ago. But our victory against these scourges is not complete. The pathogens that cause these diseases are still with us. Last year, there were about 60 million cases of whooping cough worldwide, for example. And about one million cases of measles were recorded in 2019, the year before the COVID pandemic. The bugs that cause these diseases are lurking in other countries of the world, waiting for us to lower our guard and give them a chance to roar through our kids once again.

What keeps them in check? Why are these diseases so rare in the United States? The reason is that we have been very good at vaccinating our children overall. The greater the proportion of our population that is immune from an infectious disease, the harder it is for the bug to find a susceptible person to infect. And when you make it harder for the bug to find a susceptible person to infect, it is less successful at jumping from an infected person to infect another. At some point, this becomes so difficult that each infected person ends up infecting less than one new susceptible person.  And the pathogen, when introduced into a population with a large proportion of immune individuals, cannot get a foothold. It just sputters out. This is the point that we know of as herd immunity.

Herd immunity requires a large proportion of your population to be vaccinated against the pathogen for it to work. And the more infectious a pathogen is, the greater the proportion of vaccinated people you need to prevent the bug from getting a foothold and taking off. For example, for measles, over 90% of the population needs to be vaccinated to reach herd immunity. But since we have been requiring childhood vaccinations to attend school, we have been able to keep our vaccination rates high enough to maintain herd immunity in general. But the COVID epidemic disrupted the normal process of childhood vaccinations for many. And the anti-vaccination forces emboldened by the COVID epidemic have made many parents reluctant to have their children vaccinated.

So, if we are pretty close to herd immunity anyway, what is the harm in not getting my child vaccinated, so long as almost everyone else does so? Well, there are two reasons to do so. First, people who decide not to vaccinate their children are not randomly distributed among the population. People who are against vaccinations (for whatever reason) tend to cluster into groups. And it is easy for the overall vaccination rate in such a group to fall below the level needed for herd immunity. Then that group is vulnerable to infections once again. We have seen this recently in measles outbreaks in New York and California. So you can never be sure that your child's peers are vaccinated and your kid is protected. A second reason is that there are children out there that cannot be vaccinated and so remain vulnerable to these infections. These include not only kids with immune deficiencies of one sort or another but also infants, whose immune systems do not develop until after the first few years of life. There have been recent cases of infants dying from whooping cough because they contracted it before they were old enough to get vaccinated. Losing a beloved baby is a tragedy no one wishes to inflict upon another.

So for your own child's health and safety and the health and safety of all those other kids who cannot get vaccinated, please do the right thing and make sure your child's vaccinations are kept current. We all need to work together to keep these scourges at bay. Childhood vaccines are safe and effective and will protect all if we all step and do the right thing.

Thomas Unnasch is a Distinguished University Professor in Global and Planetary Health with the USF Health College of Public Health at USF and an infectious diseases expert.