I don't believe the actual Mark itself will be an vaccine or "medicine", given that these treatments are taken from a supposed self-interest (personal health) perspective. Meanwhile, the Mark of the Beast will be an exterior pledge of allegiance if you will to another being and/or his system.

There is disagreement on the timeline.

St John Eudes and the Early Church Fathers held that the reign of Mary comes after the Anti-Christ unlike the other prophecies that state it comes before.

The Antichrist is a real man. In fact, it is every man who worships himself (or mankind) rather than the Holy Trinity. He thinks that Jesus was a "really good teacher" because he sacrificed himself for other men. We should do the same to overcome all the problems that the world is facing--especially climate change, racism and anti-semitism. He learned this "doctrine of Jesus the man who becomes a god" by attending the Novus Ordo and reading all the magisterial docuмents of "Pope St. John Paul II" and "Pope Francis."

Regarding the "groundwork," please read this post on that subject. And yes, by my definition above, JPII was "the Antichrist" but so are all other men who share his views expressed in the encyclical Redemptor Hominis, which by the way includes all of those believers in the current religion of "woke."

I understand what you are saying. I am disagreeing that "the Antichrist" has not been revealed. The Antichrist is most of the world elite and their enablers, who are persecuting those faithful to the Holy Trinity and the authentic magisterium.
 
All of those people are "the Antichrist" because the governments and corporations are not enabled by a single man in our world. There is no Roman emperor in democratic-socialist societies. The "people" manipulated by the elite and their media propaganda machine enable the entire Antichristian apparatus, the multi-tentacled Leviathan. Those who are on-board with the religion of woke and covidocracy are "the Antichrist" because without their support, the craziness would not be happening.

I know this sounds "out there." So I can understand if you disagree with me. I think it will become clearer as we move forward.

That is the Mystery of Iniquity, we were warned there would be false prophets and false Christs. But there will be a singular man who will embody this spirit, known as the Antichrist. The Fathers and theologians are clear about this.

Is what the Fathers and theologians taught about the Anti-Christ/Mark of the Beast, etc. considered infallible Church teaching?  Or is there room for speculation since it does not appear to be settled doctrine?

Nevertheless it is certain, in fact Suarez holds it as an article of faith, that Antichrist is a definite individual. The words of St. Paul to the Thessalonians leave no room for doubt in this matter. -The Apocalypse of St. John, p. 130; ref. 2 Thess. 2:3-9.

His idea of Antichrist is exactly that of St. Paul, that he is not on impersonal power but a man. “Little children, it is the last hour: and as you have heard that Antichrist cometh, even now there are become many antichrists” (1 Jo. II. 18, 22; IV. 3). St. Paul had expressed the same view: “unless there come a revolt first and the man of sin be revealed . . . etc.” (2 Thess. II.), leaving no doubt of its being a man. -The Book of Destiny, p. 19

The ancient Fathers identify the Beast with Antichrist. Irenaeus says he will establish his capital at Jerusalem (Adv. Haer. V. xxv. 4); Hippolytus in his treatise on Christ and Antichrist identifies him with the fourth beast of Daniel and also with the Beast of the Apocalypse. Hippolytus was a disciple of Irenaeus, who in turn was well acquainted with Polycarp, a disciple of St. John. Their interpretation of the Apocalypse should therefore have some weight. Modern interpreters largely identify the Beast with the Roman Empire or the Emperor. Such an interpretation is untenable and contradicts itself and the text on many points. -Kramer, p. 260

The Beast will be a man, “the man of sin”. He will be known as Antichrist when he has established his empire. And this will be the seventh and last of the godless world-empires that promoted idolatry, emperor-worship, devil-worship and persecution of God’s people. He will be the incarnation or embodiment of the beast which in ancient times engendered every blasphemy. Satan was the soul of those empires, and through them he promoted his world-control. Those empires were the Egyptian, the Assyrian, the Babylonian, the Medo-Persian, the Grecian and the Roman. The ruling dynasties of those empires persecuted the people of God and aimed at destroying the true faith and worship. Hence the character of Antichrist, as it were, pre-existed in those ancient dynasties. When he appears in the world in person, his antichristian character will reach the fullest development of evil man. -Kramer, p. 304

The beast is not the aggregate of infidels, heretics, enemies and persecutors of the people of God but a person. He is Antichrist, who had not yet appeared when St. John wrote his first letter (1 Jo. II. 18). St. Paul speaks of the same person, when he says: “he sits in the temple of God, showing himself as if he were God”. This could not be said of a world-power or organization of any kind but only of a person....The height of iniquity is reached when a man poses as God and demands divine honors for himself. Though this was done by rulers of kingdoms and empires, Antichrist will make the boldest pretensions to the possession of divine prerogatives. -Kramer, pp. 306-7

Antichrist will be a human being, a particular man, not a system, a regime or an ideology. We know this for certain from Scripture, from Patristic writings and also from private revelations, although the latter, alone, would not constitute a definite proof.

• "Christ arose from among the Hebrews, and he (Antichrist) will spring from among the Jews. Christ showed His flesh as a Temple, and raised it up on the third day; and he, too, will raise up again the Temple of stone in Jerusalem." (St. Hippolytus)
• "Antichrist, the son of perdition will be born in Corozain, will be brought up in Bethsaida and shall begin to reign in Capharnaum, according to what Our Lord Jesus said in the Gospel: "Woe to thee Corozain ... woe to thee Bethsaida ... and thou Capharnaum that art exalted up to heaven, thou shalt be thrust down to hell. (Luke, 10:13) Antichrist shall work a thousand prodigies on earth. He will make the blind see, the deaf hear, the lame walk, the dead rise, so that even the Elect, if possible, shall be deceived by his magical arts. Puffed up with pride, Antichrist shall enter in triumph the city of Jerusalem and will sit on a throne in the Temple to be adored as if he were the Son of God. His heart being intoxicated with arrogance, he will forget his being a mere man, and the son of a woman of the tribe of Dan." (St. Zenobius)
• "Antichrist will be born of Jєωιѕн parents, of the tribe of Dan, but his mother will not be a virgin, as many believe. As the Holy Ghost came into the heart of Mary, so will the devil enter into the mother of Antichrist, and his diabolical power will always support him. Babylon will be his birthplace, but he will be reared and instructed in Bethsaida and Corozain. After his education at the hands of malignant spirits he will go to Jerusalem and place his seat in the Temple which he will have restored. He will submit to the rite of circuмcision, claiming that he is the Son of the Omnipotent God. His first converts will be kings and princes. His influence will extend from sea to sea, largely through force and persuasive eloquence. He will perform many signs and great miracles. Those who believe in him will be marked on the forehead with a sign. For three and a half years he will hold sway and, at the end of that period, he will put to death Henoch and Elias, who will have previously opposed him by preaching the true faith. Shortly afterwards, Christ will appear, and Antichrist will be killed by Michael the Archangel." (Adso the Monk, 10th Century)
• "And we beseech you, Brethren, by the coming of Our Lord Jesus Christ and of our gathering together unto Him: that you may not be easily moved from your sense, nor be terrified, neither by spirit, nor by, word, nor by epistle as sent from us as if the day of the Lord were at hand. Let no man deceive you by any means, for unless there come a revolt first and the man of sin be revealed, the son of perdition, who opposeth and is lifted above all that is called God, or that is worshipped, so that he sitteth in the Temple of God, shewing himself as if he were God." (2 Thess., 2:1-4)
• These few passages suffice to show that Antichrist will be indeed a man. They show also by way of implication that he will not be an atheist for his claim of being God and the Son of God is in itself an acknowledgment that God is not a mythical being as the Communists assert. Further, he will gather together the Jєωιѕн people - hardly what the Communists are endeavouring to achieve. That anyone should say, write, and write again in spite of all remonstrances, that Communism is Antichrist leaves one baffled.
• I now propose to present further evidence to show the absurdity of such a contention. In each case I invite the Reader to pause and ask himself if these passages fit Communism.
• "In every respect that Deceiver seeks to make himself appear like the Son of God. Christ is king of things celestial and terrestrial, and Antichrist will be king upon earth. The Saviour sent the Apostles unto all the nations, and he, in like manner will send false apostles. Christ gathered together the dispersed sheep, and he in like manner will gather together the dispersed people of the Hebrews. Christ appeared in the form of man, and he in like manner will come forth in the form of man." (Hippolytus)
• "This impious man ... will give orders that he himself shall be worshipped as God. For he will say he is Christ, though he will be His enemy. That he may be believed he will receive the power of doing wonders, so that fire may descend from heaven, the sun retire from its course and the image which he shall have set up may speak. And by such prodigies he shall entice many to worship him, and to receive his sign on their hands or foreheads. And he who shall not worship him and receive his sign will die with refined tortures. Thus he will destroy nearly two parts, the third will flee into desolate solitudes. But he, frantic and raging with implacable anger, will lead an army and besiege the mountains to which the righteous shall have fled. And when they shall see themselves besieged, they will implore the help of God with a loud voices and God shall hear them, and shall send to them a Deliverer ..." (Lactantius)