Life in the Time of Coronavirus - Brought to you by Dr. MZ
Why Herd Immunity is Not the Answer
As we chafe under the constraints of social distancing and sheltering at home, we long for an answer to release us from cabin fever and return us to our “normal life.” One notion being floated out of desperation is the “wash over” concept: Let’s just let this virus wash over us, producing herd immunity.
Herd immunity is the concept that a virus will not circulate in a human population that is largely immune to that virus. It is not necessary for everyone to be immune, only that each infected person transmits the virus to less than one susceptible person for transmission to ultimately stop. Randomly the virus encounters mostly people who are immune and hence transmission slows and fizzles out. The best example is measles (rubeola) virus which is notoriously contagious. In a susceptible population, one person with measles will infect between 15 and 18 other people (R naught) meaning that measles spreads like wildfire. In order for herd immunity to stop measles transmission, 95% of the population must be immune through wild type immunity (got the actual disease and survived) and through vaccination. Each time our US population falls significantly below 95% immunity due to failure to vaccinate, measles circulates again.
SARS- CoV-2 is not as wildly contagious as measles. The R naught for SARS-Cov-2 in a susceptible population is estimated at 5.7, potentially as low as 3.8 or as high as 8.9. This means that herd immunity for SARS-CoV-2 would require that the population be at least 70% and immune. With no vaccine, this would require that at least 70% of the population be infected with this virus and develop protective immunity. Currently, the case fatality rate (CFR) for COVID-19 in the US stands at 5.9%. That number is squishy so let’s assume that the CFR is closer to 3%. If we allowed this virus to “wash over” us to produce herd immunity (however temporary that might be), nearly 7 million Americans would die (70% X US population of 328 million = 229,600,000, 230 million X 3% = 6, 900,000). To put that number in context, about 675,000 Americans died in the 1918 Influenza Pandemic. More deaths would occur among older adults and those with underlying health conditions but young people do die with COVID-19. Of the total deaths in New York City (as of April 14, 2020) 4.5% were in the 18-44 year age groups, 23.1% were in the 45-64 age groups. Multiply those percentages by 7 million Americans and you get large numbers of dead younger people.
What happens to people who recover from COVID-19? We have hints that all may not be benign. We know little about the short term complications of COVID-19 and next to nothing about the long term sequelae of COVID-19. We do know that COVID-19 is a systemic disease infecting virtually every organ. We know about brain inflammation, Guillain-Barre Syndrome, about renal failure, about abnormal liver enzymes, about blood clots and strokes and COVID toes in younger people. A report that caught my eye was of a pulmonary critical care physician who recovered from COVID-19 only to discover that she was left with a cardiomyopathy. Cardiomyopathy means that your heart muscle doesn’t function well, a condition that leads to heart failure, and is addressed ultimately with heart transplant.
We know from studying other viruses that some viral diseases produce sequelae many years later. Examples include Subacute Sclerosing Panencephalitis (SSPE) presenting 6-10 years after having measles, Post-Polio Syndrome which occurs many years after polio, Encephalitis Lethargica which presented as an neurologic epidemic in the years following 1918 and may have been a consequence of the 1918 Influenza Pandemic, and chicken pox which lingers as a latent infection, only to reappear years later as Herpes zoster (shingles). The long term sequelae of COVID-19 are entirely unknown and won’t be known for some time. The idea of deliberately subjecting 230 million Americans (70% immune) to these unknown questions as a grand experiment is jaw-dropping.
Our only option is to endure varying degrees of shut-down and social distancing while therapeutic and vaccine trials are conducted. Finding therapeutic agents with benefit will lower the fatality rate. Finding a therapeutic agent with prophylactic value, to be administered to exposed people to abort disease, would be extraordinary. The combination of wild type disease and widespread vaccination may ultimately bring us to herd immunity but that time is in the future. In the meantime, discipline, restraint, patience, compassion, public health measures, and help for those in dire straits will keep deaths to as few as possible.
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Dr. Margan Zajdowicz is the Co-Chair of the League of Women Voters-Pasadena Area Healthcare Committee and a retired infectious disease physician who spent many years in clinical practice and emergency preparedness and pandemic planning for the US Navy. She holds a Doctor of Medicine degree from the University of Maryland School Of Medicine and a Master of Public Health degree from Old Dominion University/Eastern Virginia School of Medicine.
