HERD IMMUNITY

Happy Easter to everyone.

Someone asked my about herd immunity and the concept of “flattening the curve”.

I’ll work on the latter issue but for now, here is an explanation about herd immunity and why we should not assume it will happen.

HERD IMMUNITY

The term “herd immunity” refers to the phenomenon of a disease disappearing from a population once enough members of that population have been exposed to, or have been immunized against, a particular microbe. Once you have antibodies to a particular bug, your body has a better chance of identifying and destroying the microbe the next time you are exposed to it. Once enough people have antibodies, the micobe can’t reproduce and spread from individual to individual as readily. The term obviously came from the animal agricultural industry where, because of overcrowding along with unhygienic and unhealthy conditions, diseases can run rampant. As an example, Bovine Leukemia Virus (BLV) is present in 100% of cattle herds in operations with more than 500 animals. In smaller operations, the rates vary but tend to be in the 70-90% range. As an fyi, the largest cattle operation in North America has more than 940,000 cattle! BLV IS transmitted to humans and has been linked with breast cancer. There actually is a vaccine for this disease and it has been used successfully in other parts of the world, all but eradicating BLV, but it costs money to immunize all those cattle and unfortunately, public safety is often trumped by financial considerations in the US.

Herd immunity can happen in two ways:
1) Many people contract the disease and in time build up an immune response to it (natural immunity).
2) Many people are vaccinated against the disease to achieve immunity.

The percentage of people that must have immunity to safely slow or stop an infectious disease is called the “herd immunity threshold.” For some diseases, particularly ones which have a slower mechanism of spread, herd immunity can go into effect when as few as 40% of people in a population become immune to the disease. But in most cases, 80-95% of the population must be immune to the disease to stop its spread.

Measles is a good example of an infectious disease which needs ~95% of people to be immunized, or have contracted the disease thus generating antibodies, for there to be herd immunity in a population. The recent trend of parents electing not to immunize their children is responsible for the re-emergence of not only this disease, but also Mumps and Rubella. Usually all three are combined into one vaccination, MMR. I’ve posted many times about my feelings about immunization and won’t get into it here (BTW, I’m for it!).

Not every illness that has a vaccine can be stopped by herd immunity. For example, tetanus is contracted from bacteria in your environment. Tetanus does not pass from person to person, so herd immunity doesn’t work for this infection. Getting the vaccine is the only protection. The same is true for Hepatitis B.

There are several reasons why herd immunity isn’t a realistic answer to stopping the spread of the new coronavirus, SARS-CoV-19:
1) There isn’t yet a vaccine for SARS-CoV-2. Vaccinations are the safest way to practice herd immunity in a population but this is still months, if not more than a year away.
2) The research for antivirals and other medications to treat COVID-19 is ongoing and is also not likely to be available in the near future.
3) We don’t know if you can contract SARS-CoV-2 and develop COVID-19 more than once, i.e. develop innate immunity like you do for chicken pox or mono.
4) Doctors don’t yet know exactly why some people who contract SARS-CoV-2 develop severe COVID-19, while others do not. We just don’t understand the mechanisms yet. Although initially it was thought to mostly affect the elderly and those with chronic diseaes, there is a significant number of youger, healthy people who are getting really sick and dying.
5) Hospitals and healthcare systems may be overburdened if many people develop COVID-19 at the same time. We are starting to see the rate of infection starting to slow but if restrictions on movement are loosened too soon, the disease will likely blossom again.
6) Since this has been an overwhelming disease with lethal consequences, simply waiting for herd immunity to develop is not practical. Many more people will die in the meantime.

Herd immunity can help stop the spread of illness, such as swine flu (H1N1), and other pandemics within an entire country. But it can change spontaneously, as is the case with the yearly regular flu, and it doesn’t always guarantee protection against any disease.

For most healthy people, assuming herd immunity will occur isn’t a good alternative to getting vaccinated but that is still to be developed. In the meantime, the best practice is the standard fare:

• isolation
• social distancing
• frequent handwashing and hand sanitizing if you must go out.
• doing all you can to stay healthy by eating well, exercising, managing stress and being as positive as possible.

Stay safe and be well.

AC 😎✌️🌱❤🐖🏃🏻🧘🏻‍♂️🌎