What does herd immunity mean?

Herd immunity is defined as a proportion of a population that is immune to a pathogen. If we can get this proportion to be high enough, the pathogen cannot get a foothold within a population, and people that are prone to infections will be protected. At least 60% of the population would need to be immune to SARS-CoV-2 for each society to reach herd immunity. With 7.8 billion humans, that would mean 5 billion people would need to be immune to SARS-CoV-2. However, considering that SARS-CoV-2 is a novel virus, it is unclear what severity of case produces immunity to SARS-CoV-2 and how long this immunity lasts. As a result, it is unclear how long herd immunity would last even if we were able to achieve that 60-70% herd immunity to SARS-CoV-2. 

Consider the concept of life-long immunity, which is the idea that a single vaccine dose or infection is sufficient to protect you from further exposures to that same virus. Immunity responses to measles and mumps are very stable. So much so that it can last a lifetime. However, infections with the milder forms of SARS-CoV-2 don’t provide lifelong immunity. From previous research on other types of coronaviruses, it has been determined that coronaviruses infect humans in a 2 to 3-year cycle and don’t tend to induce long-lasting immunity. When 14 volunteers were infected with a form of these viruses, 1 year after their first exposure, 6 individuals became infected again and were able to shed the virus. These individuals did not get a cold, and their shedding of the virus was shorter with the second exposure, but this study and others highlights how coronaviruses do not seem to mount lasting immunity. Whether this is the case with SARS-CoV-2 remains to be determined. However, the ability of vaccines to provide lasting protection depends on these findings. 

Let’s look at scenarios for how vaccination levels can play out:

Situation 1: No one is vaccinated

Image explaining herd immunity. The shown scenario is when no immunized individuals are present

Situation 2: Some of the population is vaccinated

Image explaining herd immunity. The shown scenario is when a small number of immunized individuals are present

Situation 3: Most of the population is vaccinated

The immune system is very effective:

Although we may not know all the details around the immune response to SARS-CoV-2, we know that the virus can over stimulate the immune system, causing negative effects on our health and ultimately our immune response wins in most individuals. 

Our immune system is capable of protecting most of us from sickness and death associated with SARS-CoV-2. But let’s help out our immune systems by reducing exposure to the virus and giving ourselves the best chance against winning!

As the province starts to open up, it is up to each and every one of us to get vaccinated and protect ourselves, our friends and families and our community from getting infected. Do your part in getting vaccinated. Guildview pharmacy offers Moderna vaccines. Give us a call at 416-283-5388 to book your first or second dose appointment today.

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