A vaccine is a biological preparation that provides active acquired immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future.
If your parents are anti-vaccination, or against the Covid vaccine specifically, and they do not wish to take the vaccination due to a medical condition, which you also suffer from, and out of fear of you getting worse, then you must consult with a specialist and see what they recommend.
If your parents are against Covid for any other reason, and not due to health difficulties you suffer from, then it would not be a sin if you take the vaccine without their knowledge. However, if they have specifically said to you that they will, for example, disown you if you get it, etc, then I would suggest you try to rationalise with them to avoid problems.
With prayers for your success.
Any injection of vaccination or any other injection of medicine does not harm fasting at all.
Thank you for your question. There is no problem in taking the covid vaccine or other vaccinations in the arm whilst fasting.
May you always be successful
Answers should be given with certain knowledge, and no one here (as far as I know!) has certain knowledge about everything that is happening outside of our experience or eyes.
Also, no one can give certain knowledge about the long-term effects of a new substance or medication, even if there is no ill intent, until time passes and we come to understand the complexity of effects. Certainly there are many substances that were originally thought to be safe and now we know they are dangerous.
So, basically, no one here can give a full answer to "is it safe".
However, if you are unsure about whether or not you should receive a vaccine, I suggest (a) talking to researchers or health professionals about it, (b) considering your situation and people around you (for instance, are you in a high-risk profession or are people in your household particularly vulnerable) and making the best decision, and (c) if that does not work, do istikahra.
Yes, it is not only allowed but but also required to protect yourself and your family and friends. It can become obligatory if it is the only way to avoid a dangerous disease.
It depends on the way of using the vaccine.
If such vaccine is to be taken orally, it will Haraam to consume it.
But if it is not taken orally but injected in the body or dropped in the nose with out letting it go inside the stomach, then it will be allowed.