Zaid Alsalami, Shaykh Dr Zaid Alsalami is an Iraqi born scholar, raised in Australia. He obtained a BA from Al-Mustafa University, Qom, and an MA from the Islamic College in London. He also obtained a PhD from... Answered 7 months ago

Bismihi ta'ala

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.