As we all know, Covid-19 is a new virus for humans, and hence we know very little about this entity.
But, for a virus that has been a menace for only 4 months, we have learned an immense amount, through the aggressive research by the various academicians around the world.
Let’s try to understand some basic immunology of Covid-19.
*** This is VERY difficult to explain in “simple terms” ***
What is Covid-19?
- Covid-19 = Corona Virus Disease identified in 2019
- Covid-19 is an RNA virus (which is different from DNA, but a genetic material nonetheless)
- Under magnification, the Covid-19 virus appears to have a “crown”
- “Coronam” is the Latin term for “crown” ==> hence the name “Corona”
How long does the Covid-19 infection last?
- If you have a “normal” immune system, your body will attack the virus and kill it over a period of 1-14 days
- Your immune system and the immune response will determine the exact duration of infection
- Since it can survive in your body for upto 14 days, you remain infectious for that duration
- Hence, the rationale for a 14 day quarantine
How long can it survive OUTSIDE of your body?
- It can survive on ANY surface for upto a “few days”
- The exact duration is not 100% known
- But, based on other viruses, it is assumed it can survive for a few hours on any surface
- If Covid-19 behaves like other such viruses, heat and humidity will kill the virus much more rapidly
- Hence, the whisper that the virus will “die off” once summer arrives
Currently Available Test – Covid-19 Genetic Test
- The “genetic code” for this virus was identified and sequenced fairly quickly by a Chinese scientist
- Once the “genetic code” was sequenced, scientists very quickly developed a diagnostic test to identify segments of this genetic code
- This is the test that is currently being used in the US
- As long as you have the virus in your throat or upper respiratory tract, a cotton swab of your throat can be tested for the genetic code
- But, as soon as your infection is cleared, and the virus is no longer found in your throat, the genetic test will turn “normal”
- Hence, as of March 23, 2020, the genetic test will ONLY tell us if you have a CURRENT, ACTIVE INFECTION
- It does NOT tell us if you previously had an infection
- The way our body fights any infection is through the “immune system”.
- One of the components of the immune system is called an “antibody” (abbreviated “Ab”)
- There are various “types” of antibodies
- 2 important antibody types for fighting such infections are IgM and IgG
- Normally, a new infection will trigger the natural creation of IgM Ab
- After a certain amount of time, IgG Ab are created
- Depending on the type of infection, the time it takes to develop IgM or IgG Ab will vary.
- IgM Ab will typically disappear after the infection is treated
- IgG Ab will linger for many months to years after the infection is cleared
- Since the Covid-19 science is still emerging, we do NOT know how long it takes for any individual to develop IgM or IgG Ab
- Typically, we CANNOT get re-infected with the same virus AFTER our body has created IgG
- IgG will fight off any re-infection by the same virus
- So, theoretically, we should only get this infection once
New Tests on the Horizon – Covid-19 Antibody Tests
- As recent as earlier today (March 23, 2020), various Pharma companies have submitted requests to approve a new ANTIBODY test
- These new tests do NOT test for the genetic material
- Rather, they test for the Ab
- Some of the new tests will detect IgM, while others will detect IgG
Summary of Immunology
- After an infection, your body creates IgM and IgG Ab
- IgM Ab can be detected EARLY in an infection
- IgG can be detected LATE in the infection cycle
- If you are able to detect IgM Ab with lab testing, that will indicate a new or recent infection
- If you are able to detect IgG Ab with lab testing, that will indicate an OLD infection
- But, IgG does not tell you WHEN the infection occurred — whether the infection occurred a few months ago or a few years ago
How will these different tests (Genetic and Antibody) be used?
- Over the next few weeks, we will probably see a multi-prong testing approach
- We will probably use the genetic test to look for ACTIVE infection
- We will also use the IgG Ab test to see if an individual HAS PREVIOUSLY had the infection
- This is important, because if we develop IgG Ab from a previous infection, our immune system can now fight off any new infection, and most likely, we will not get the infection again
- Hopefully, if you have IgG Ab, you can resume your normal life, without fear of getting the infection again
How does a vaccine work?
- When we are given a vaccine, we are given part of the viral genetic code
- This partial genetic code allows our body to self-create IgM and IgG Ab, without getting the actual infection
- A successful vaccine induces our bodies to create IgG Ab, which is used to fight off any new infection
Stay Safe !
- Sudhir S. Athni, MD