Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Brother, thanks a lot for your question, which shows how far you are interested in keeping yourself abreast of the Islamic affairs and Shari`ah teachings relating to day-to-day issues.
First of all, you are to know that the Prophet (peace and blessings of Allah be upon him) instructed us saying: “Seek medical treatment, for Allah has not created an illness without creating a cure for it.” This Hadith should be taken as encouragement to try to address any disease that seems to be incurable.
Moreover, when the Prophet (peace and blessings be upon him) was ill, he sought medical treatment. He showed us that seeking precaution through a powerful medicine or herb is necessary to help the human body against the attack of germs and viruses. This goes in line with the legal rule “Prevention is better than cure”; the rule is taken from the Hadith; “There should be neither harm nor reciprocating injury.” (Malik)
Responding to the question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Immunization against possible or future occurrences of diseases does not contravene our faith in the Unseen (ghayb) as an exclusive knowledge of Allah. As believers, we are fully convinced that matters of the Unseen are known only by Allah. At the same time, Islam teaches us that we must plan and prepare ourselves for contingencies and presumed harm based on our understanding of being Sunnat-ullah (laws of Allah) in creation.
We know from the Qur’an and the Sunnah that the universe functions according to the law of causation, and as believers we are taught by the Prophet (peace and blessings be upon him) that we should not simply wait for the miracles to happen, rather we should make use of causes to obtain benefits or remove harm. The Prophet (peace and blessings be upon him) was always planning in advance for every move; he was a real strategist as a leader, and this in no small measure stands as the cause of his astounding success in his mission.
Once a nomad came to the Prophet (peace and blessings be upon him) and reported that he had left his camel unleashed in the desert trusting that Allah would take care of it. The Prophet (peace and blessings be upon him) told him he should have rather tied his camel first and then put his trust in Allah.
Therefore, taking all necessary precautions to prevent presumed harm or diseases is perfectly in the permissible limits of the Shari`ah. If one still needs to be convinced, we may refer to the story of Prophet Yusuf (peace and blessings be upon him) who, as an economic planner, prepared in advance for the future by introducing wise and accurate strategy.
There is no reliable jurist who has held such a strange view you referred to in your question. Therefore, our advice to those people who are venturing such fatwa utterances is to fear Allah and not to close the door of mercy and latitude in the Shari`ah.
Allah Almighty knows best.