Recent concerns have been raised about the Johnson & Johnson Covid-19 vaccine and its use of abortion-derived stem cells in its development and production.
The U.S. Conference of Catholic Bishops has recently come out with a statement addressing this issue. They have stated that: "While we should continue to insist that pharmaceutical companies stop using abortion-derived cell lines, given the world-wide suffering that this pandemic is causing, we affirm again that being vaccinated can be an act of charity that serves the common good".
In short, it is morally permissible to receive the Johnson & Johnson vaccine. The USCCB simply asks Catholics, when it is possible, to prefer the Pfizer and Moderna vaccines over the Johnson & Johnson option. At the same time, the USCCB recognizes that this may not be possible, and given the extreme danger posed by Covid-19, "it is morally acceptable to receive Covid-19 vaccines that have used cell lines".
You can check out the full statement here.