I am not a biology student and this question came in my mind out of nowhere.
I read somewhere that the vaccines contain some denatured or almost dead corona viruses and when these are injected in our body , our immune system remembers them and if the actual (killer) corona virus enters our body , our body recognises it and quickly attacks it.
But if we have a corona patient his body has already identified the corona virus and so if the vaccine is given the body will not have much changes to do and simply refuses it .
So is it okay to give the covid vaccines to a covid patient ? Can it make the infection even worse ?
In short, no. It's not harmful but it won't do anything to prevent or mitigate the current infection.
How vaccines work in general is that they train the immune system to respond to an infection so that they are prepared for it. Generally protein component of the virus or an inactivated form of the pathogen is used as a vaccine. The immune system recognises the proteins as 'foreign' and develops anti-bodies to fight them. Then you are immunised to the virus without having to suffer the symptoms of infection. Vaccines work before you are infected as a preventative measure. Then when you are infected, the immune system is prepared and can fight of the virus with the antibodies already developed since the virus has the same "antigen" proteins as you immune cells have already been exposed to from the vaccine.
So what happens when you are vaccinated when you are already infected? Basically nothing.
The benefit of a vaccine is a head-start to train your immune system how to fight it to prepare for the early stages of infection. If you are vaccinated, your immune system will destroy the virus before the it multiplies or gives you symptoms. If you've already been infected then the active virus has already infected many of your cells and multiplied into many copies. Adding inactivated viral particles or spike protein antigen won't help your immune system, it's already been exposed to them by the ongoing infection. Your immune cells are just playing catch up to the infection that's already taken hold. The virus has already stormed the beaches and the immune cells were not prepared. Vaccination now is arguably pointless. They will eventually produce antibodies against the virus already in your system even if you weren't vaccinated.
Lasting immunity after recovering from infection is not guaranteed and a vaccine could give immunity to other strains. For these reasons, it could still be recommended by medical professionals if you've already been infected. However, you need to be vaccinated before exposure to the virus for it to be effective. A vaccine is not a treatment.
Note: the currently available AstraZeneca, Pfizer, Moderna, and Johnson & Johnson vaccines for SARS-CoV-2 do not contain live or inactivated coronavirus. They trick the host system into producing the spike protein from instructions carried by the vaccine.
Citation for clinical application: Jenner, E (1798) An Inquiry into the Causes and Effects of the Variolae Vaccinae.