Herd Immunity means you have reached a level that protects most of us from becoming ill from a virus or other infective agents. Currently, researchers have in the past believed you must achieve immunity levels of 70% for the population to be immune.
More than a dozen scientists are now rethinking this age-old idea. There is a growing belief that Herd Immunity can be achieved at only 50% of the population developing resistance to the infective agent.
In the case of covid19, we must look at the population as a whole. The formula of Herd immunity is calculated from the epidemic’s so-called reproductive number, R0, an indicator of how many people each infected person spreads the virus to.
The truth is that there are real-world variations in immunity, resistance to infection which can be age, and risk dependent. Also, there is a growing belief that many of us may already have cross-immunity from other coronaviruses which allow our bodies to prevent a virus from infecting us and making us ill. Also, some children it is theorized do not have viral receptors and as a result, this virus does not have the ability to bind with them and reproduce itself.
Many affective communities during the so-called first wave may already have immunity from initial exposure and there is growing evidence that a second infection is unlikely, which would help reduce or eliminate a second wave which is merely the first wave that is inexperienced as people begin to get back to normal habits of shopping and gathering.
Right now, there is growing evidence that even light cases of covid19 confer durable immunity, meaning that you have a strong lasting immunity after exposure. With all the talk about a vaccine, it is important to understand that a vaccine is an exposure, but so is being in the proximity of someone who has the virus which causes an active immunity. The CDC offers explanations of the different types here. Once you are vaccinated, the body develops an immunity which is known as immunization.
Are they right? Check out this fascinating article in the NY Times
What if ‘Herd Immunity’ Is Closer Than Scientists Thought?
In what may be the world’s most important math puzzle, researchers are trying to figure out how many people in a community must be immune before the coronavirus fades.
By Apoorva Mandavilli Aug. 17, 2020
We’ve known from the beginning how the end will arrive. Eventually, the coronavirus will be unable to find enough susceptible hosts to survive, fading out wherever it briefly emerges.
To achieve so-called herd immunity — the point at which the virus can no longer spread widely because there are not enough vulnerable humans — scientists have suggested that perhaps 70 percent of a given population must be immune, through vaccination or because they survived the infection.
Now some researchers are wrestling with a hopeful possibility. In interviews with The New York Times, more than a dozen scientists said that the threshold is likely to be much lower: just 50 percent, perhaps even less. If that’s true, then it may be possible to turn back the coronavirus more quickly than once thought.