Herd Immunity Op-Ed

There has been much debate around the concept of herd immunity since the early stages of the COVID-19 pandemic. As a public health term, the idea of herd immunity is that if enough people are protected against an infection because they have been exposed and developed antibodies, transmission of the infection slows and ultimately new outbreaks are halted because much of the population is no longer susceptible. Some people suggest that COVID-19 can best be controlled by allowing the virus to run its course and achieve enough numbers of infected persons to reach herd immunity. We suggest that there is some confusion about the use of this term and that there are strong reasons for not pursuing that approach.

In modern times, herd immunity has never been achieved by allowing a disease to run through the population unfettered. It has only been achieved by mass vaccination programs. Measles, rubella, diphtheria, mumps, pertussis, polio, chickenpox have all been controlled through vaccination, and herd immunity to these diseases has been achieved in many places in the world. The devastating smallpox virus was eradicated by achieving worldwide herd immunity through vaccination.

Without a vaccine, current knowledge suggests that about 70% of our residents would need to be infected before we reach herd immunity. A recent UCI/Orange County Health Care Agency study found that about 11-12% of our population has already been infected. If we allowed everyone to become infected until we reached the herd immunity “threshold” of 70%, about 2,240,000 Orange County residents would need to become infected. Given an estimated infection fatality rate of between 0.25% and 0.35%, between 5600 and 7,840 of them would die. Another 1,344,000 would get sick with COVID-19 symptoms, and 4%, or 89,600 people, would need hospitalization. Additionally, there is accumulating evidence that there are significant post-viral syndromes which may occur in some people even after the virus has passed. A “run its course” strategy will significantly affect the entire health care system not only for COVID patients but for all patients, creating shortages, putting stress on resources, and limiting access to health providers and staff. If we allowed the virus to spread, unimpeded, we would add thousands more deaths, overflow our hospitals, lose millions of work-days, and expose thousands of people to the long- term chronic conditions that affect many survivors of severe COVID-19, before we ever achieve herd immunity.

The best approach to taking control of COVID-19 is to build immunity through vaccination. Recent, promising results have indicated that the first vaccines to be approved are approximately 95% effective. The roll out will likely occur in limited supply, by the end of the year. Next year in winter/early spring 2021, as the supply of vaccine increases, eventually everyone will be able to be vaccinated.

If we learned anything from the previous reopening in late May, it is that we need to be cautious and maintain social distancing, limited group activities, and wearing face coverings as much as possible, so we don’t return to the soaring number of cases we experienced before. If a vaccine is available by the end of the year or soon after, herd immunity can be achieved relatively painlessly so long as a sufficient proportion of our fellow citizens avail themselves of it. This is vastly preferable to a gigantic increase in the number of our fellow citizens dying and completely overwhelming our healthcare system.


Bernadette Boden-Ablala, MPH, DrPH

Director and Founding Dean, Program in Public Health

Professor, Department of Population Health and Disease Prevention and Department of Epidemiology

Susan and Henry Samueli College of Health Sciences

University of California, Irvine


Dan M. Cooper MD

Associate Vice Chancellor for Clinical and Translational Science

Principal Investigator, UC Irvine CTSA

Professor of Pediatrics

Chair, University of California BRAID


Clayton Chau, MD, PhD

Agency Director

County Health Officer

OC Health Care Agency


Casey Dorman, PhD

AOC Health Care Agency