We live in a godless society and there are countless evils around us. For example, in some places, for some diseases (like chickenpox), one can only obtain vaccines whose manufacturers used cell lines from murdered babies, as disease cultures for manufacturing the vaccine.1
The conciliar church is lax and liberal and approves receiving vaccines which come from the cell lines of murdered babies, unless there is an alternative vaccine which does not use murder. But there are three reasons it is wrong to accept these vaccines manufactured using the cell lines of murdered babies:
  1. Using those vaccines promotes future murders.
  2. Using those vaccines rewards persons connected with the murders.
  3. We incur guilt for those murders, by our consent.
Below, we discuss each of these reasons.

1. Using those vaccines promotes future murders.

Using the cell lines from murdered babies encourages future murders whenever pharmaceutical companies deem it to be convenient and profitable to commit more murders for use in vaccine research or production. 
Because people did not refuse vaccines coming from the 1960s-era cell lines taken from murdered babies, drug companies, labs, and researchers felt “free” to commit more murders to create new cell lines. For example, a new cell line from a new murdered baby, was announced in 2015.2
Accepting those vaccines manufactured through murdered babies, promotes future murders (and every murder of an innocent human is a murder too many)! Thus, when you use a vaccine produced through murder, the drug companies are encouraged to commit additional murders to keep vaccine production high.

2. Using those vaccines rewards persons connected with the murders.

It is wrong to use vaccines produced from murdered babies because using these vaccines enables manufactures to profit through the murders. We should not help drug companies make wickedness profitable!

3. We incur guilt for the babies’ murders, by our consent.

We become culpable for someone else’s sin by consenting to it.3 When St. Paul teaches us this truth about sharing someone else’s sin by consent, he mentions murder in particular. Here are his words:
Being filled with ... murder, ...  they who do such things, are worthy of death; and not only they that do them, but they also that consent to them that do them.
Romans, 1:29-32 (emphasis added).4
A person is guilty of a murder by consent when he acquiesces5, even passively6, or accedes, even reluctantly,7 to the murder. When we use vaccines which come from murder, we are (at least) passively accepting—i.e., giving in8 to—the murders that make those vaccines available.

A person can incur guilt by consenting even after the murder.

Some types of sharing in someone else’s sin can only occur before the sin is committed, e.g., commanding or advising that the sin should be committed. See, the above list (from The Penny Catechism) of ways to share someone else’s sin.
However, consent to the sin is different. A person can consent to (i.e., acquiesce in) a murder either before or after it is committed, and so can incur guilt either way.
St. Thomas Aquinas teaches that a person can incur guilt by consenting to a murder which has already been committed. He applies this principle (of guilt through post-murder consent) to a person who joins the Jewish religion after Christ’s murder. Here are St. Thomas’ words:
When a person becomes a Jew, he becomes a participant in the killing of Christ.
St. Thomas Aquinas, Lectures on St. Matthew, ch.23, #1861.
By using those vaccines manufactured through the murders of babies, a person thus incurs guilt by consenting to (i.e., acquiescing in) the murders of those babies even though murders were already committed.

The passage of time does not erase the guilt of consenting to those murders.

A superficial objection could be raised that the vaccines were made from murdered babies more than five decades ago and surely that is “so long ago” that we should disregard the murders because they are too distant in time.
That is wrong. God does not cease to treat a murder as murder merely because of the passage of time.9 Those who commit murder and those that consent to it, remain culpable. The mere passage of time does not remove the need to repent. The punishments of hell are forever because the passage of time does not erase guilt.
Just as God does not overlook culpability for murder simply because of the passage of time, man does not do so either. In the civil law, there is typically no statute of limitations for murder.10 In other words, no murder is ever so remote in time that we “don’t worry about it”.
The murdering of the babies committed to “harvest” their cell lines, was premeditated and is first degree murder. The passage of time does not change the guilt of the murders and does not eliminate the guilt of a person who consents to the murders.
No matter how much time passes, faithful and informed Catholics will never buy the vaccines manufactured through these murders!

The end does not justify the means

Another superficial objection could be raised that vaccines do much good and that they save so many lives that this “outweighs” the murders through which the vaccines are produced. However, faithful and informed Catholics must never be complicit in evil because of “good” that can come from it.  The end does not justify the means!

Discerning God’s Will through standing up for principle.

A similar, superficial objection is that without receiving these sinful vaccines, I will lose some opportunity, for example, the chance to enter (or send my dependents to) a particular school. Again, the end does not justify the means!
If, despite your best efforts, you cannot receive a “conscience waiver” or “religious exemption” to attend (or send your dependents to) the school without receiving a sinful vaccine, that merely shows you that God does not want you to attend that particular school, etc.

We are not justified in consenting to even the smallest of sins, much less, consenting to murder.

The evil at issue here is murder.  That is a very grave evil.  But even if a person were to suppose that receiving vaccines derived from the cell lines of murdered babies were “only” a venial sin, even the very smallest sin is an infinite evil in three ways.11 We should be ready to die rather than commit any sin. 
Here is how St. Alphonsus de Liguori, Doctor of the Church, warns against committing even the smallest sin:
A single venial sin is more displeasing to God than all the good works we can perform.
St. Alphonsus de Liguori, Uniformity with God’s Will, §6.
Here is how St. John of the Cross, Doctor of the Church, warns us that the road to hell begins with a small sin:
Our Lord said in the Gospel: “He that is unfaithful in little will be unfaithful also in much.” For he that avoids the small sin will not fall into the great sin; but great evil is inherent in the small sin, since it has already penetrated within the fence and wall of the heart; and as the proverb says: Once begun, half done.
Ascent of Mount Carmel, Book III, ch.20, section 1.
Here is how John Henry Cardinal Newman declares that the smallest sin is worse than all the physical suffering in the world:
The Catholic Church holds it better for the sun and moon to drop from heaven, for the earth to fail, and for all the many millions on it to die of starvation in extremest agony, as far as temporal affliction goes, than that one soul, I will not say, should be lost, but should commit one single venial sin, should tell one willful untruth, or should steal one poor farthing without excuse.
Apologia Vita Sua, by John Henry Cardinal Newman, Image Books, Doubleday, Garden City, New York, © 1956, p.324.

Information about which vaccines to refuse.

We must be informed Catholics. This sometimes means doing our own research, if we cannot obtain reliable information from our doctor. Here is a list of sinful vaccines the use of which connects a person to the murders of those babies. The list also identifies ethically permissible alternative vaccines where they are available.
If your doctor does not cooperate in your decision to refuse sinful vaccines, get a different doctor!

Conclusion

Some vaccines are produced through cell lines obtained from murdered babies. There are three reasons getting these vaccines is a sin:
  1. Using these vaccines promotes future murders.
  2. Using these vaccines rewards those connected with the murders.
  3. We become culpable for the murders, by our consent.
We should stand up for Christ and reject these sinful vaccines. We should also urge others to stand against these vaccines which break God’s Law (including the Natural Law). At our Judgment we would want to have done so!
  1. Here is a list of vaccines connected with murder and ethical alternatives, if they exist: https://cogforlife.org/wp-content/uploads/vaccineListOrigFormat.pdf↩
  2. https://cogforlife.org/2015/09/09/new-aborted-fetal-cell-line-emerges-for-vaccine-production/↩
  3. Here is summary of this basic truth from a common catechism:

    328. When are we answerable for the sins of others?

    We are answerable for the sins of others whenever we either cause them, or share in them, through our own fault. 

    329. In how many ways may we either cause or share the guilt of another's sin? 

    We may either cause or share the guilt of another's sin in nine ways:

    1. By counsel.
    2. By command.
    3. By consent.
    4. By provocation.
    5. By praise or flattery.
    6. By concealment.
    7. By being a partner in the sin.
    8. By silence.
    9. By defending the ill done.
    Quoted from The Penny Catechism, Nihil Obstat, Joannes M.T. Barton, S.T.D., L.S.S., Censor deputatus, Imprimatur, Georgius L. Craven, Epus Sebastopolis, Vicarius Generalis, Westmonasterii, die 20a Junii, 1958, p.57 (emphasis added).↩
  4. Here is the longer quote from St. Paul:

    Being filled with all iniquity, malice, fornication, avarice, wickedness, full of envy, murder, contention, deceit, malignity, whisperers, detractors, hateful to God, contumelious, proud, haughty, inventors of evil things, disobedient to parents, foolish, dissolute, without affection, without fidelity, without mercy. Who, having known the justice of God, did not understand that they who do such things, are worthy of death; and not only they that do them, but they also that consent to them that do them.

    Romans, 1:29-32↩
  5. One of the definitions of consent is: “acquiescence to or acceptance of something done or planned by another”. https://www.thefreedictionary.com/consent↩
  6. One of the definitions of acquiescence is: “passive assent or agreement without protest”. https://www.thefreedictionary.com/acquiescence↩
  7. Two of the definitions of accede are: “to consent” and “to give in”. https://www.thefreedictionary.com/accede↩
  8. Two of the definitions of accede are: “to consent” and “to give in”. https://www.thefreedictionary.com/accede↩
  9. St. Thomas Aquinas teaches the principle that a person is culpable for consenting to a murder even when that murder had been committed many centuries earlier. St. Thomas applies this principle to a person who joins the Jewish religion long after Christ’s murder. Here are St. Thomas’ words:
    When a person becomes a Jew, he becomes a participant in the killing of Christ.
    St. Thomas Aquinas, Lectures on St. Matthew, ch.23, #1861.
    Thus, St. Thomas teaches that even the passage of a long, long time (1200 years, in St. Thomas’ time) after the murder, does not remove the culpability for consenting to it. In other words, there is no “end date” for culpability by consenting to murder after it was committed.
    Note also regarding St. Thomas’ own example, that he places culpability upon consent to the murder of Christ (through conversion to Judaism), not upon ethnic lineage of a person. Thus, this culpability does not touch the Apostles or any other ethnically Jewish persons who did not (do not) consent to the murder of Christ.↩
  10. Here is how one legal commentary summarized the state of the law:
    Some crimes have no statutes of limitations. As an example, murder typically has
    none.
    https://resources.lawinfo.com/criminal-defense/criminal-statute-limitations-time-limits.html
    Here is how the New York courts explain that murder does not become a non-prosecutable crime because of the passage of time:
    Statutes of limitations are laws which say how long, after certain events, a case may be started based on those events. If the statute of limitations has run out, a case should not be started in court. If a case is started after the statute of limitations has run out, it is called time barred. A defendant or respondent can ask the court to dismiss the case if it is time barred by the statute of limitations.
    Statute of limitations laws are based on fairness. Over time, memories fade, evidence is lost, and witnesses disappear. People get on with their lives and don’t expect court cases from events in the past—unless a really horrible crime has been committed.
    The amount of time by when a person or agency can start a case is different depending on the claim. For example, cases about real property have a long time period, while slander and libel have short time periods. Some crimes, like murder, are so terrible that they often have no limitations period.
    Except for when a government agency is sued, there is almost always at least one year from the date of an event to start a case no matter what type of claim it is. You should have no statute of limitations worries if you file your case within this one-year period.
    https://nycourts.gov/CourtHelp/GoingToCourt/statuteLimitations.shtml↩
  11. For a full explanation of this truth that all sin is an infinite evil in three ways and mortal sin is an infinite evil in a fourth way too, read this article: ../faith/the-infinite-evil-of-sin.html↩