Chances are you've heard of herd immunity - but like most folks, you don't know how it really works. Fortunately, the experts at the U.S. Government Accounting Office's Science Technology Assessments and Analytics team and the medical journal JAMA have recognized how important it is to look at what we know and don't know about it and get the facts out to you.
Defining herd immunity: The STAA says "A population can establish herd immunity to an infectious disease once a large enough portion of the population - typically 70 percent to 90 percent - develops immunity. Reaching this "herd immunity threshold" limits the likelihood that a non-immune person will be infected. This process slows or stops the spread of the disease." For polio, for example, 80 percent to 86 percent of the population must be immune for the spread to slow or stop. For measles, it is very high — 91 percent to 94 percent.
For COVID-19? It's unknown. That is because we do not yet know:
- The herd immunity threshold (how many folks it takes to achieve herd immunity from infection or vaccination).
- The number of secondary cases typically generated by an infected individual (the typical spread is one to seven, says the JAMA Health Agencies Update).
- The viral mutation rate (because the virus can change enough to escape the effect of antibodies that squelch a previous version of the infection).
- The length of time immunity lasts. Measles and polio typically last a lifetime; immunity to influenza, just a year or so. For COVID-19, it may vary, depending on the intensity of the individual infection.
What attempts at herd immunity for COVID-19 have shown: In Sweden, where the government opted to try to achieve herd immunity, there have been far more deaths than in neighboring Scandinavian countries where measures were taken to stop the spread. Sweden has had 574 deaths per million people in contrast to Denmark's 108 deaths per million, Finland's 61 deaths per million and Norway's 49 deaths per million.
Best guesses at what would give the U.S. herd immunity: Stick with us for this ... we need to go though some preliminary info.
1. The U.S. population is 328,000,000. As of this writing, we have had 8,028,332 COVID-19 cases and 217,918 deaths. That's around a 3.6 percent fatality rate - but most asymptomatic infections probably aren't detected. That's why the Centers for Disease Control and Prevention uses 0.65% as its fatality rate in pandemic planning scenarios. (To really figure the fatality rate we need more data on the rate of asymptomatic infection.)
2. Based on the World Health Organization figure of a 65 percent infection rate for herd immunity (lower than the STAA figure) and the CDC's 0.65 percent fatality rate, 213,000,000 people in the U.S. would need to become infected to achieve herd immunity. That would leave 1,385,800 Americans dead from COVID-19. That could deliver a hospital bill of $80 billion - or even higher.
Vaccinations as a route to herd immunity: Polio, hepatitis B and C, and rubella are just some of the once-devastating diseases that a have been eliminated from the U.S. by the continued use of vaccines. The measles vaccine had delivered that same widespread protection. But last year, there was a spike in cases because of people skipping the vaccine - 1,282 cases in 31 states, the largest number since 1992.
There's no way to know when enough effective COVID-19 vaccines will be available to confer herd immunity on the country - or if one or two vaccinations will provide permanent protection or you'll need an annual shot.
So you heard it here - don't bank on naturally-occurring herd immunity. The price paid in human suffering and medical costs (as indicated above) may be too high. Until an effective vaccine is available to everyone, it is each person's responsibility to limit community spread by wearing a mask - indoors and out - washing hands frequently, maintaining social distancing and limiting gatherings. Let's get back to work but do it wisely and safely.
Mehmet Oz, M.D. is host of "The Dr. Oz Show," and Mike Roizen, M.D. is Chief Wellness Officer Emeritus at Cleveland Clinic. To live your healthiest, tune into "The Dr. Oz Show" or visit www.sharecare.com.
Distributed by King Features Syndicate, Inc.