Antibodies against covid 19 is not synonymous with protection against the disease.
Antibodies are different types and different kinds.
There can be Ig E, Ig G, Ig M and Ig A type antibodies. Some of them are neutralising ( kill the virus) and some other can be enhancing ( damage our lungs on behalf of the virus).
Take the example of Dengue. An antibody in the first attack of Dengue increases the severity of second attack. Therefore second attack of dengue usually becomes more severe than the earlier one. This is called enhancement. We still don’t know whether the antibodies against Covid will do same thing or not. But we certainly know that all the lung damages that occurs following a Covid attacks are immune mediated. The virus per se is not fatal. It is the over reaction of our own antibody system that kills us. Therefore while most of the covid attacks are symptomless, yet few young healthy victims unexpectedly go into respiratory failure. We still don’t have a marker for them. We know that their antibodies are responsible for these damages.
Antibodies stay for variable periods in our body.
We believe that 3 months after an attack of Covid, the antibodies vanish in the serum of the victim. We don’t know whether this indicates loss of protection or not. We also don’t know how long the antibody would stay after two doses of vaccine.
” The fact that antibody levels are falling doesn’t mean we haven’t got a memory response.”
—Sheena Cruickshank, University of Mancheste
Our body’s defence against virus is not limited to antibodies alone.
There are two types of defence cells in our body: B cell and T cell. B cells take a photograph of the virus on the first encounter. They design antibodies against the pictured virus. On subsequent encounter they pour out these antibodies. That is their job. We have developed tests to measure these antibody level in our body.
But nature’s defence is much more complicated than our imagination. We know that T cells play a major role against virus attacks. We have T helper cells, T killer cells and so on. We still don’t have wide access to quantify them. We do not know what is the role of these T cells in a corona infection and whether mere absence of antibody leaves us unprotected.
Summary–
Mere presence or absence of antibody against Corona Virus does not spell immunity or lack of it against the disease.
Vaccination should not be linked to measuring antibody level. We are not clear about its significance in our body’s defence. At least the present teaching is that mere presence of antibody should not bar one from vaccination.
Our defence is better linked to the gap between last infection. An infection within 4-8 weeks from today strongly suggests that probably you are protected. So vaccination can be safely deferred. This is again an assumption.
Dr Ramakanta's Ideas 