Where human rights come from
Catholic understanding of natural law is the law that God implants in every human being when He creates human nature as opposed to animal nature. The human soul then is equipped with a conscience that informs reason to act according to what is proper to human nature. When someone thinks, feels, wills, or acts against human nature, he/she is always breaking natural law by definition.
Catholic understanding of human right in relation to natural law can then be simply defined as the dignity, blessing, and privileges proper to the human soul so the person can achieve one possible end / telos fit for human nature. This is a right given by God (who created each human soul) by the simple virtue of his/her existence. Whether sinner or saint, damned or saved, rich or poor, baby or adult, this human right is a gift from God not earned by anyone, and therefore the withholding of this right by another human being is an offence against the giver, God. The victim can then appeal to God as his/her prosecutor. All celebration in the Psalms about God's justice (such as Psalm 98) is the expectation that God will eventually punish the perpetrator and restore what was "stolen" to those who "cry out" to Him.
Criteria of human laws to be consistent with natural law
We also have to consider our participation in a country (through an implicit social contract), a country with human law that we need to obey. Aquinas defined the validity of human law as possessing 4 properties:
- Ordination of reason (i.e. follow natural law principles)
- For the common good (i.e. not corrupt, or end up injuring the common good)
- By one who has care for the community (i.e. by justly elected / appointed official having jurisdiction)
- Promulgated (i.e. published through a channel that everyone has access to; no surprises, no secrets)
Therefore if a government creates a "social distancing" / "contact tracing" rule which has the above 4 properties, natural law will not have a problem with it. This is even though the rule does limit freedom of movement or does require giving up some private location and social connection. But this giving up for the sake of contact tracing is consistent with our dignity because this rule is for the common good (property #2) so we willingly give up some freedom (NOT giving up right, which is not ours in the first place, but God's) as a "give and take" (benefiting from the common good created by the laws of the country while voluntarily relinquishing some freedom).
There are only positive rights under Thomistic natural law
Because it is God who gave us all human rights through our nature, all human rights are then positive rights, framed as existential rights for us to grow to fulfill our end / telos. To the person who receive this gift from God he/she is responsible to cultivate it in a certain direction as a farmer cultivates land to produce crops, or as in the Parable of Talents. The rights should then be seen as the foundation and raw material for producing goals consistent with human nature, rather than entitlement we can use for something that would not please God.
In Thomistic natural law, negative commandments like "Do not murder", "Do not steal", etc. do not create rights but serve as a hedge of protection to preserve the integrity of existential rights of individuals living in a society. They should then be part of the fabric of laws derived from social contracts which in turn are "insured" by the power of a government. In other words, a social contract which respects natural law creates those "negative rights" to protect the inalienable "positive right" granted by God to individual human beings.
From individual perspective, a human being exercising his/her God-given right can freely enter into a social contract. Even though entering the social contract restricts some of his/her freedom & privacy, it's consistent with natural law because by nature human being is a "political animal", needing a society to develop his/her potential.
No right to privacy under natural law, but right to dignity & flourishing
How then should we construe the "right" to privacy? As explained above, in Thomistic natural law principle there is no "right to privacy" per se, only right to human dignity and right to "flourish in relative freedom" under God, our giver. Because human nature has a social component, what's good for our community will be good for us. Therefore, when in times of hardship some regulations / laws are enacted which reduce our freedom (social distancing) and privacy (contact tracing), as long as this rule is reasonable (property #1), is for the common good (property #2), is enacted & enforced by lawful official (property #3), and is clear & stable (property #4), this temporary reduction is consistent with natural law.
Right to privacy derived from social contract
BUT we DO have a "right to privacy" in the social contract realm, which maybe framed as "negative right" (I don't know the details), through the available constitutional means. Natural law theorist would not see privacy as an end in itself, but only as a means to ensure the dignity and flourishing goals of a human being. Thus privacy has limits that should be connected with what makes sense for that society in a particular situation so the society can creates a best-possible condition for individuals in it to flourish. The classic examples are 1) the "freedom" to say "fire" in a crowded indoor theatre, or 2) the "privacy right" to not provide the password of a smartphone to a law enforcement official acting under a lawful order which fulfills the 4 properties above.
Combining natural law and social contract, what we Christians can do is to advocate for our elected / appointed officials to use their wisdom to create and implement contact tracing in a way that minimizes the reduction of privacy according to the 4 principles above. We Christians (especially those in IT) can contribute our technical ingenuity to offer ways to do contact tracing that is more secure, revocable, limit access to authorized officials, and having as little privacy-divulging footprint as possible. We can also maximize our "rights" as parties in the social contract to use 1) legal means (lawsuit) if we feel the privacy reduction unreasonable (against property #1), 2) "freedom of speech" to promote our view, and 3) lawful participation for political change.