Every day, we encounter billions of germs, but they’re not all bad. Intangible but effective, Immunity ensures resistance against harmful microorganisms from entering the body and causing disease.
Humans primarily have two types of immunity — innate and adaptive
It is acquired naturally by the body. Everyone has this basic, general protection. For instance, the skin acts as a barrier to block germs from entering the body. Innate immunity is sub-divided into two types:
- Non-Specific innate immunity, which is general resistance offered to all the infections.
- Specific innate immunity, where a distinct resistance specific to a microorganism is displayed.
It develops gradually through a person’s lifetime. When exposed to a disease or when immunized against it with the vaccine, our body develops adaptive immunity. It can be sub-divided by how the immunity was acquired:
- Active immunity: It is naturally acquired immunity through accidental contact with a disease-causing agent. It can be acquired through the transfer by injection (or infusion) and promises long-term immunity, sometimes life-long. 
- Passive immunity: It is artificially acquired through deliberate actions. It is “borrowed” from another source and lasts for a short period of time.
Passive immunity can occur in a couple of ways:
- Maternal antibodies: Unborn and newly born babies are protected by antibodies from the maternal immune system. These antibodies are shared in two ways: across the placenta and in breast milk.
- Immunoglobulin treatments: In certain situations, antibodies obtained from animals, from other people, or synthesized in a laboratory can be used to treat individuals at risk of infections.
A third category, community or herd immunity, does not involve physical components of the immune system for protection. Yet, it dampers the spread of disease as majority of the population is immune to it. Usually, 50% to 90% of a population needs immunity to achieve herd immunity, depending on how contagious the infection is. Based on early estimates of SARS-CoV-2 infectivity, at least 70% of the population is likely needed to be immune to have herd protection. This prompts reduction and, thus, elimination of the disease.
Tune in to know more about immunity in our coming chapters.