Herd Immunity

Sun, 04/05/2020 - 10:00am

Like many, I have been listening nonstop to the radio and reading about the Covid-19 pandemic. It’s hard to avoid. What’s even harder is assimilating it all in a way that does not make one feel helpless and vulnerable.

I am not a doctor, an immunologist, or a statistician. I’m just a lay person in my seventies trying to put it all together. And I certainly have not put it all together. But this morning a few things became clearer to me. And my insight was facilitated by understanding one term. Herd Immunity.

Herd immunity is a Darwinian concept. An infectious disease moves through a herd of animals, or people. The older, debilitated (immune compromised) and sometimes the very young often die from the disease. The younger healthy animals, or people, usually survive, but not always. The infectious pathogen (virus or bacteria) is passed from host to host. The hosts’ immune systems see the invading pathogen and say “you don’t belong here”, and muster an army of soldiers called antibodies to destroy the pathogen. Some invading pathogens like Covid -19 are very infectious and virulent, that is to say able to attack and weaken the victim quickly. The immune system of the old, infirm and very young may not be able to summon enough antibodies quickly enough to destroy the invading pathogen. They become very sick and may die. In the healthy younger host, the antibodies kill the pathogens and the host becomes sick but usually lives. I say usually, because there is a growing number of seemingly healthy young Covid-19 victims who are dying of the disease. Importantly, the surviving host keeps its antibody army in reserve. So if that pathogen or even one very similar to it ever invades that host again, the army is ready to quickly destroy its enemy. Once the disease has moved through the herd leaving only the healthy immunized young in its path, the pathogen cannot find new hosts who are not protected by antibodies. Once between 80 and 90 % of the herd’s members are protected by antibodies, the pathogen begins to die out and will often become extinct. At that point we have herd immunity. For many thousands of years before antibiotics, vaccines, anti-virals and social distancing that was the normal course of an epidemic or a pandemic.

Another way to achieve herd immunity is to vaccinate. A vaccine is usually a protein or portion of a protein which appears to the host’s immune system to be the pathogen against which we are trying to protect ourselves. Again the host says “you don’t belong here” and musters an army of antibodies. So if the real pathogen ever invades that vaccinated host, the reserve army is standing ready to attack the invader and protect the host. But here again, to reach herd immunity, we need to vaccinate 80 to 90% of the herd. And of course to do that you need an effective vaccine.

A stop gap measure is to treat infectious diseases with anti-infective drugs. There are many antibiotics which are effective in treating bacterial infections. But they are not effective in treating viral infections, like Covid-19.

Likewise there are several effective antiviral drugs approved for use in viral infections. But they are effective against only a select number of viruses usually when used early on. It is not yet known whether any of these anti-viral drugs or even other approved drugs for non infectious diseases will be effective in treating Covid-19.

For a drug to be used to treat disease or for a vaccine to be used to prevent disease requires rigorous well controlled clinical trials in thousands of patients comparing the experimental drug to existing therapies or placebo. Both private industry and government agencies around the world are working day and night to develop new compounds and vaccines and to conduct trials with every potential candidate drug or vaccine. Under the very best of circumstances, those trials will take more time than we have. And without such trials, we run the risk of doing far more harm than good.

So there seem to be three options.

1. Darwinian herd immunity which would cost millions of lives in the United States alone.

2. We develop a new or existing therapeutic and fast track it through clinical trials.

3. We develop a new vaccine on a similar fast track schedule.

Number one is happening whether we like it or not. And numbers two and three are also happening. But no matter what you hear, two and three are one to two year scenarios at best. And by then you have default Darwinian herd immunity.

So what can we do? Well, there is actually a third way to achieve herd immunity. If you cannot vaccinate in time, and you reject Darwinian selection, you isolate the virus.

You say that’s what we are doing?

No. I’m sorry my friends. We are not. We are not even close. People right here in our town are walking in packs on hiking trails, gathering next to each other outside closed coffee shops, going to post offices and touching public surfaces, and wandering around grocery stores and pharmacies without masks. People are standing in lines outside grocery stores next to each other. People from out of state hot spots are coming to our towns. And parents are letting teenagers out to meet with their friends! Bottom line is that a substantial part of the population is not taking this seriously enough to get us to herd immunity. All we are doing is bending the slope of the curve down a bit to slow, but not stop, the spread. That will leave the virus viable in pockets all over the country from which it will emerge in subsequent waves the way the Spanish flu did two more times in 1919 and 1920.

Personally, I hate big or little government in my life. But for the safety of the public at large, it’s time government did the right thing and not just close schools and public facing businesses. Everybody who is not volunteering or deployed helping those sickened with the virus should be quarantined for a minimum of two weeks. I mean quarantined in the sense of police (or National Guard) enforced law. It’s one of those rare cases like yelling fire in a movie theater when the need for public safety surpasses the individual’s rights.

Raymond Egan is a resident of Boothbay.