 Serologic testing, that is a detection of presence of antibodies in serum of people, helps us to determine how much percentage of population had been infected with the coronavirus, because there might have been some very mild cases or cases with no symptoms known as asymptomatic cases. So these cases might not have got RT-PCR tests done and we would not know the actual number of people who got the infection. So checking for antibody response helps us detect actual percentage of people who got infected, since all of them would develop an antibody response. These antibodies appear in blood few weeks after infection. So this serological testing actually tells about past infection. But these days the question is arising that whether we should get an antibody test after vaccination, because everybody is in fear and wants to know that whether their antibody response is adequate after vaccination. In this video we will address this question that should you get an antibody test after vaccination, if not then why not and if yes then which test you should get done and why. Now just like after infection antibodies appear in blood after approximately two weeks of first dose of vaccination and approximately after first week of second dose of vaccination. Now remember that all vaccines against COVID target the synthesis or delivery of spike proteins in the body and the antibody response after vaccination is against these spike proteins present on the coat of the coronavirus. But you see when someone gets infected body produces antibodies against various proteins present on the coat which includes obviously spike proteins but other proteins also like nucleocapsid protein. So if you plan to get an antibody test after vaccination you have to be very careful which tests you are getting done. See after vaccination if you get a test done which detects antibodies against nucleocapsid proteins the test will be negative since after vaccination the antibodies are produced only against spike proteins. So you may panic that oh my god that even after vaccination my body has not produced any antibodies which is wrong. Since you are not aware that which test you got done and you don't know that this test will be positive only after infection and not vaccination. So you won't understand what's happening. Also if such a test is positive that doesn't mean that you are protected since these nucleocapsid proteins are present bit inside and despite the presence of these antibodies the virus may be able to enter the cells since it is the antibodies against spike proteins which prevent virus entry into the cells. Anyways now suppose you get the proper test done that is the the test which detects antibodies against the spike proteins and you get a positive test but you don't get a good antibody titer. Titer is basically a value which is used to measure how much antibodies are produced so the unit for this is international units per ml. So suppose the antibody titer is less than 10 international units per ml. This 10 international unit is generally considered as the cutoff. Now is it justified to start panicking or saying that vaccine is ineffective because my antibody titer is less than 10 international unit per ml? Well no because there are three things. First even if your antibody response is low that doesn't mean that body is incapable of fighting with the virus. If you have seen my video on how Covishield works you will understand that it's not only the antibodies which fight with the virus but there are certain cells known as killer T cells too. If the virus manages to enter into cells these killer T cells kill the infected cell itself. Secondly nobody in the world actually knows what is a good antibody titer that means that if you have antibody titer above this particular value then we can say that okay for sure you are protected it's not like that we don't have that data yet. Moreover even if you have good antibody titer say suppose defined by the cutoff remember that there are mutant circulating against which antibodies may not be protective but your cell mediated immunity that is killer T cells will be and finally remember that antibody response varies from person to person depends on a number of factors even the time duration of response varies. So should you get the antibody test and after vaccination? My answer is there is no need since we don't know what is good antibody response and even if you have less number of antibodies that doesn't mean that your body is incapable of fighting with the virus. So good and bad response both don't mean anything. Fundamentally in one line if I say antibody tests are not recommended to assess the presence of immunity against covid following vaccination but if you are hell bent for taking the test make sure you get tested for spike protein antibody after vaccination and do remember everything which I told you in order to interpret the results properly otherwise you may go either into pseudo satisfaction and may become careless in following the precautionary measures or you may unnecessarily panic. Well hopefully this video helped you in understanding the antibody testing after vaccination. If it helped do press the like button share the video with others to help spread the knowledge and subscribe to the channel Physiology Open for more such updates. Thank you.