What’s wrong?Do the math: “herd immunity” is not an ethical option without the COVID vaccine-Entertainment and Life-MetroWest Daily News, Framingham, Massachusetts

Q: Can I get things back to normal and get herd immunity?

A: Herd immunity occurs when a large part of the community (flock) is immune to the disease. When this happens, the disease cannot spread significantly in terms of the number of newly infected people, as it “encounters” a sufficient number of people who are already immune (although the limited outbreak of cases remains. It can occur). Expansion.

Think of this as a raging forest fire. Firefighters try to get over it by setting fire and burning out certain parts of the forest. , Already burned the fuel in a fire, or was “immunized” by a firefighter intentionally igniting it. In the case of a rapidly rampaging fire, this strategy may not work because the fire can spread in different directions in the “non-immune” area. Or you could even “jump” a firebreak created by a firefighter. Therefore, the strength and speed of fire spread, in this analogy similar to the infectivity of the disease being dealt with, determines how much forest a firefighter needs to burn to control it.

It is estimated that 70% of the population must be immune to COVID-19 to reach herd immunity. For comparison, measles is even more contagious than the SAR-Cov-2 virus, and it is estimated that 94% of the population must be immune to obtain herd immunity from the disease. ..

So how can we get a threshold ratio for the population that is not affected by SARS-Cov-2? There are two methods, vaccination and infection.

Since we don’t have the vaccine yet-we hope to get an effective and safe vaccine soon-why don’t we allow people to get infected? Let’s do math.

There are 330 million people in the United States. The threshold rate is 330 million times higher, so if you take 70%, 70% is equivalent to 231 million people who need to be immunized by being infected. Overall, about 2% to 3% of people infected with SAR-COV-2 die (mortality is higher in the elderly and lower in the young), and 2% of the 231 million people are 4.5 million. More than one person has died. Hope we all agree, but it’s not a good approach!

However, the mortality rate of COVID-19 is higher in the elderly and those with comorbidities, so what if everyone over the age of 45 remains isolated? (Of the population of 330 million, about 170 million are under 44 and 160 million over 45.) Isolate 170 million and 160 million. What if you want to revive as usual?

Unfortunately, the virus spreads to people under the age of 45, so it definitely “jumps” to many people over the age of 45. But for now, let’s ignore this and do the math.

Make all the very optimistic assumptions. Let’s say an infected person under the age of 20 does not die (the mortality rate of this population is low, but unfortunately it is not zero). This leaves 108 million people between the ages of 20 and 44, 70% of whom, or 75.6 million, need to be infected. For these people, let’s say the mortality rate is 0.1% (that is, 99.9% recover from the disease, which isn’t really that high, but we’re optimistic here!). 75.6 million x 0.1% is equivalent to 75,600 people.

Calculations show that group immunity is achieved if you are willing to sacrifice more than 75,000 neighbors and friends under the age of 45 and keep out 170 million people over the age of 45 (although ” Flock “only) People under 44 years old).

Does this seem like a really rational option for an ethical and caring person? Are 75,000 healthy people under the age of 45 dying and keeping 170 million over the age of 45 out? I hope not to do so. However, as mentioned above, infecting everyone in the country alone would kill at least 4.5 million people.

It should also be noted that the above discussion assumes that immunity to SAR-COV-2 lasts long enough to reach and maintain a threshold ratio.

So how can we achieve herd immunity in an ethical and rational way? The answer is vaccination. If you have a vaccine that works 70% (optimistic goal) and you want to vaccinate basically everyone in the country (which is a very important point), you will reach that! However, we know that too many people refuse the vaccine. Even knowing that doing so puts the lives of many friends and neighbors at risk.

I hope that seeing the math people will give us a better understanding of what we are dealing with and the complexity of the problem. And we hope this encourages more responsible behavior from people, including vaccination when safe and effective vaccines are available!

Jeff Hersh, Ph.D., MD can contact Dr Hersh @ juno.com.