Read Part One here.

Imagine a world where parents were free to decide whether to vaccinate their children without consequence. Some might still choose vaccination, but many would not—whether from misinformation, fear of side effects, religious beliefs or simple neglect.

The first consequence would be a decline in herd immunity. Viruses thrive in gaps. If measles vaccination rates dropped below 95 percent, outbreaks would spread like wildfire. If polio immunization rates fall below the 85 percent herd-immunity threshold, poliovirus could return to America from regions where it still exists.  A disease once nearly eradicated could again cripple children and adults within weeks.  The three polioviruses could mutate (change), leaving those already immunized for polio vulnerable once again.  The percentage of paralysis rates could be sky high. 

The second consequence would be greater vulnerability of those who cannot choose. Infants too young for vaccines would be left exposed in a world where contagion lurks. Cancer patients undergoing chemotherapy, organ transplant recipients and people with immune disorders would live in constant danger. The very people society has a moral obligation to protect would be sacrificed to misplaced notions of “personal freedom.”

Learn from history

The dangers of optional vaccination are not hypothetical. They have played out repeatedly in history.

Measles in Europe: In the 2010s, declining vaccination rates in parts of Europe led to tens of thousands of measles cases, with dozens of deaths. The outbreaks spread rapidly among unvaccinated communities, then spilled into the broader population.

Pertussis in the U.S.: The resurgence of whooping cough in states with high exemption rates demonstrates the direct link between lax vaccination policies and disease return. Infants, too young for full immunization, suffered the worst outcomes.

Polio in Nigeria: In the early 2000s, rumors about the safety of the polio vaccine led to boycotts in northern Nigeria. The virus surged, paralyzing thousands of children and spreading to other countries that had been polio-free for years.

These examples underscore a sobering truth: When immunization falters, disease roars back.

Vaccination, trust and public responsibility

Opponents of mandatory vaccination often frame the issue as one of personal liberty. Shouldn’t parents have the right to decide what goes into their children’s bodies? While individual rights are important, public health requires balancing personal freedom with collective safety. Society accepts countless restrictions for the common good—traffic laws, food safety regulations, seat belt requirements. Vaccination mandates fall squarely within this tradition.

Trust in scientific institutions like the Centers for Disease Control and Prevention is essential. These organizations monitor vaccine safety, track adverse reactions and adjust recommendations based on evidence. While no medical intervention is risk-free, the dangers of disease vastly outweigh the rare side effects of vaccines. The measles vaccine, for example, prevents millions of deaths worldwide each year. The risk of a serious adverse event is less than one in a million. By contrast, measles kills one in every thousand infected children.

Public health is not sustained by fear but by trust: trust that vaccines are safe, trust that neighbors will also vaccinate, and trust that government agencies act in the best interest of the population. When that trust is eroded by misinformation or political polarization, the consequences extend far beyond individual families. They endanger the fabric of community life.

The potential devastation of widespread outbreaks

Beyond the human toll, the economic and social costs would be staggering. Outbreaks strain health care systems, disrupt education, and slow economies. The COVID-19 pandemic offered a painful reminder of how infectious diseases can bring modern life to a halt. Now imagine that scenario repeating, not with a novel virus, but with old foes we had already defeated.

Part Three will print in the next issue of the River Reporter.

Michael Kossove is professor emeritus and an adjunct professor of microbiology at Touro University’s School of Health Sciences.