He added that "in the Eucharist, Jesus Christ, the Risen Lord is truly present … In Holy Communion, when we receive him worthily, that is, without mortal sin, we are physically and spiritually united to Him and to our brothers and sisters in Christ. Likewise, participation in the celebration of the Eucharist on Sundays is the primary way that we keep the Lord's Day holy and so live out the third Commandment. These are some of the deepest reasons why there is an obligation and why we should freely want to fulfill this obligation."
Bishop Conley explained that the obligation does not apply "when one is physically or morally prevented from attending," giving the examples of bodily illness or having no means of reasonable transportation as ways of being physically prevented, and a parent taking care of a sick child, or if military personnel would compromise their duty for the common good, as moral preventions.
Regarding Covid-19 in particular, he said the obligation does not apply if you have been diagnosed with COVID-19 or have good reason to believe that you may have contracted it; if you are ill or have a condition that would seriously compromise your health if you contracted COVID-19; if you care for the sick, homebound, or infirmed and have a compelling reason for believing that you would infect them by going to Mass; if you have significant and grave fear or anxiety of becoming ill by being at Mass; or if you are elderly or pregnant and have a serious reason to believe you would put yourself or your child at risk by attending Mass.
Archbishop George Lucas of Omaha wrote that "those who are prevented from attending [Mass] due to advanced age, sickness, disability or some other serious reason are excused" from the obligation, and that "for the foreseeable future, those who feel they are at heightened risk of contracting or communicating COVID-19 are excused."
Bishop Joseph Hanefeldt of Grand Island wrote that the obligation "extends to all baptized Catholics who are of able body and sound mind," but that some "may be excused from the obligation to attend Mass due to advanced age, sickness, disability or some other serious reason."