Using vaccines to boost immunity against disease is lawful, for it is a means of warding off something evil before it afflicts people. It is a duty of Muslims to do their
best to ward off harm of all kinds, either before or after it comes. There is a juristic rule in this regard: Harm is to be warded off as much as possible.
as for the question in point, things are originally pure, and they become impure due to something accidental. As to whether the polio vaccine causes infertility, this is something that up to scientists to decide upon.
In fact, scientists say that the polio vaccine contains neither harmful elements nor impure ones and that it does not cause infertility at all. This refutes the arguments of those who have claimed that the vaccine is harmful and thus unlawful.
The eminent Muslim scholar Sheikh Yusuf Al-Qaradawi states the following: In fact, I was completely astonished at knowing the attitude of our fellow scholars of Kano towards polio vaccine. I disapprove of their opinion, for the lawfulness of such vaccine in the point of view of Islam is as clear as sun light. I may understand their motives and good will behind this attitude, and I beseech Almighty Allah to reward them for their good will and to forgive them what they erred in that regard.

I, together with some trustworthy scholars in the Islamic Fiqh Council held in Muscat lately, have stated and asserted the importance of the following:
First, it is a duty upon every Muslim to ward off harm as much as he can. He must not do something that may cause him harm or lead to his death. One’s self is a trust from Almighty Allah in one’s hand, and thus it is not lawful for one to cause it harm. Allah Almighty says: (And spend of your substance in the cause of Allah, and make not your own hands contribute to (your) destruction; but do good; for Allah loveth those who do good) (Al-Baqarah 2:195).
he Almighty also says: (O ye who believe! Eat not up your property among yourselves in vanities: But let there be amongst you traffic and trade by mutual good-will: Nor kill (or destroy) yourselves: for verily Allah hath been to you Most Merciful!) (An-Nisaa’ 4:29).
It was also reported that `Amr Ibn Al-`Aas (may Allah be pleased with him) performed dry ablution and led his companions in Prayer in one of the battles, though he had been in a state of major impurity and should have taken a bath for that. His companions criticized him for this and told the Prophet (peace and blessings be upon him) about it. `Amr justified his doing so to the Prophet (peace and blessings be upon him) saying: “O Allah’s Messenger! It was a very cold night and I remembered Allah’s words: (…Nor kill (or destroy) yourselves: for verily Allah hath been to you Most Merciful!) (An-Nisaa’ 4:29). Hearing that, the Prophet (peace and blessings be upon him) smiled and did not say a thing, which means he (peace and blessings be upon him) did approve of what `Amr did.
there is a juristic ruling that says: Harm is to be warded off as much as possible. This ruling is derived from the Prophetic hadith: “There should be neither harm nor reciprocating harm” (Ibn Majah, Ad-Darqutni, and Al-Hakim).
there is another relative juristic ruling in that regard: Warding off harm is to be prior to bringing about benefit.
Second, parents are responsible for providing their children as much as they can with all means of protection and immunity against harm and diseases in order to save them long-life suffering.
there is no doubt that children inflicted with poliovirus suffer a great deal and need special care, let alone the psychological and social effects they suffer from.
If there is a certain vaccine that can prevent such a disease altogether, parents are to seek to give it to their children to prevent them from being inflicted with it. If parents neglected their duty in that regard, they would incur upon themselves the sin of causing their children long-life ill health. Parents who do so would enter the category about whom the Prophet (peace and blessings be upon him) said: “It is a sufficient sin for one to neglect (those) whom he is responsible for” (Imam Ahmad, Abu Dawud, Al-Hakim, Al-Baihaqi on the authority of Abdullah Ibn `Amr).
the Prophet (peace and blessings be upon him) is also reported to have said: “[On the Day of Judgment] Allah Almighty will ask everyone in position of responsibility about those under his responsibility: Has he fulfilled his duties towards them or neglected these duties?” (Ibn Hiban on the authority of Anas).
Third, people in authority in every country are to enact laws and take actions, by means of which the health of people in general, and children in particular, is to be protected against diseases. This does not only include providing treatments for diseases, but also affording means of prevention against them. People would say that a tiny amount of prevention is better than a great deal of treatment.
Besides, it was reported in an agreed-upon hadith on the authority of Ibn `Umar (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: “All of you are guardians and responsible for your wards and the things under your care. The imam (ruler) is the guardian of his subjects and is responsible for them, and a man is the guardian of his family and is responsible for them. A woman is the guardian of her husband’s house and is responsible for it. A servant is the guardian of his master’s belongings and is responsible for them.”
During his caliphate, `Umar ibn Al-Khattab (may Allah be pleased with him) would say, “I am afraid I may be brought to account before Almighty Allah on the Day of Judgment for a goat that stumbled on the bank of the Euphrates: Why did I not pave the way so that it might not have stumbled?”
If such is the point of view of Islam regarding preventing evil and harm that may afflict even an animal, how would it be the case with preventing diseases that may cause children great suffering?
If people in authority order that a certain vaccine be given to children all over the country, people are to abide by this, for it is a duty upon them to obey rulers so long as this is done in the framework of following what is right.
Fourth, things are primarily in a state of purity. Almighty Allah says: (It is He Who hath created for you all things that are on earth) (Al-Baqarah 2:29) and (Do ye not see that Allah has subjected to your (use) all things in the heavens and on earth, and has made his bounties flow to you in exceeding measure, (both) seen and unseen?)</ b> (Luqman 31:20).
these verses indicate by implication that all things created by Allah Almighty are pure (except the few things that Almighty Allah has referred to elsewhere as impure.
hence, we are not to refer to something as impure unless there is clear evidence of this. Likewise, we are not to give a ruling to the effect that something is unlawful unless there is a certain proof in that regard.
As for the polio vaccine, there is no sign that it includes impure elements or causes infertility, and hence, it could not be described as unlawful to use.
Besides, we are to consult expert specialists in the field of medicine regarding whether this vaccine has side effects or includes impure elements. Experts are the ones who know for sure what is under the domain of their specialization. Allah Almighty says: (None can inform you like Him Who is Aware) (Fatir 35:14)
experts in the field in question, i.e., the polio vaccine, are the World Health Organization (WHO). We asked its branch in Egypt, whose staff is trustworthy and knowledgeable. They said that the polio vaccine is not harmful in any way, nor does it include impure elements or cause infertility. On the contrary, it is proved by experiment—thank Almighty Allah—to be highly effective in protecting against polio.
Fifth, polio vaccine has been used for a long all over the world, including more than fifty Muslim countries, and has proved to be highly effective in eradicating the disease. No outstanding scholar, whether from Al-Azhar University, Al-Qarawyeen University, or in the Sacred Shrines, has been reported to have objected to the use of such vaccine.< br />

Would the harm of the polio vaccine be hidden from all the eminent Muslim scholars all over the world and discovered only by our fellow scholars of Kano?
May Allah forgive those scholars of Kano and reform them. In fact, if they insist on their attitude regarding polio vaccine, they will incur upon themselves the sin of exposing the Muslim children to great harm and suffering, and hinder the effective world-wide campaign to eradicate the disease.
Furthermore, by adopting such an attitude, they distort the image of Islam and make it appear as if it contradicts science and medical progress. Islam is completely innocent of such distorted images. On the contrary, it calls for adopting healthy methods and seeking medical treatment when needed. In fact, the field of medicine has received great care in Islamic civilization.
hence, we call upon our fellow scholars in Kano to review their attitude and recant the fatwa they have given without consulting specialists or even mediating sufficiently. Right is worthy to be followed after all. There is no wrong at all if one gives up an opinion that has proved to be wrong. In this regard, it was reported that `Umar ibn Al-Khattab (may Allah be pleased with him) said to Abu Musa (may Allah be pleased with him), “Do not hesitate to review (and give up) a judgment you gave yesterday (when it appears to you it was wrong), for right is everlasting, and it is better for you to return to right than to persist in wrong.”
Should the scholars of Kano refuse to follow the advice of their fellow scholars in the Muslim ummah—which I doubt they would—I would turn to the people of Kano themselves and call upon them to vaccinate their children against polio according to the fatwa of the majority of Muslim scholars in that regard.