Colorado’s Catholic bishops are vocally opposing vaccine mandates, saying vaccination is not “morally obligatory” despite the high covid-19 death toll and citing their anti-abortion stance and their skepticism of government mandates related to “personal conscience.”

In an open letter published last week, the four Colorado bishops said that some individuals have “well-founded convictions that lead them to discern they should not get vaccinated” and discouraged the government not to “impose medical interventions on an individual or group of persons.”

The letter comes as the deadly and highly contagious Delta variant has caused a surge in cases worldwide. In response, vaccination requirements from governments and businesses have become increasingly common. Earlier this month, Denver Mayor Michael Hancock announced that the city would require its employees, as well as private-sector workers in high-risk settings like nursing homes, hospitals, and correctional facilities, to be vaccinated. The order contains an exception for those who cite religious reasons for refusing vaccination.

“We are pleased to see that in the case of the most recent Denver vaccine mandate there is accommodation for sincerely held religious beliefs,” the bishops wrote in their letter.

“We always remain vigilant when any bureaucracy seeks to impose uniform and sweeping requirements on a group of people in areas of personal conscience,” they wrote. “Vaccination is not morally obligatory and so must be voluntary.”

The letter was signed by Denver Archbishop Samuel J. Aquila, Pueblo Bishop Stephen J. Berg, Colorado Springs Bishop James R. Golka, and Denver Auxiliary Bishop Jorge Rodriguez.

The bishops also promoted the idea that covid-19 vaccines were developed using aborted fetal tissue.

“There is a moral duty to refuse the use of medical products, including certain vaccines, that are created using human cells lines derived from abortion; however, it is permissible to use such vaccines only under case-specific conditions—if there are no other alternatives available and the intent is to preserve life.”

For decades, cell lines derived from abortion have been used to manufacture vaccines, including vaccines against rubella, chickenpox, and hepatitis A, in addition to drugs against diseases like hemophilia and arthritis. Cell lines are not aborted fetal tissue, as some anti-abortion and anti-vaccine advocates falsely claim. Fetal cell lines are grown in labs and descend from cells taken from two abortions that occurred decades ago, and the cell lines that are currently used in the development of certain vaccines are thousands of generations removed from the original fetal tissue.

While the Johnson and Johnson vaccine did use fetal cell structures in its development and production, the more widely used Pfizer and Moderna mRNA vaccines did not, something the United States Conference of Catholic Bishops has recognized.

Colorado’s Catholic bishops did not make this distinction in their most recent letter, although they did urge Catholics to take the Moderna or Pfizer vaccines in lieu of the Johnson & Johnson vaccine in a letter from March.

Over 7,000 Coloradans have died of covid-19 since the start of the pandemic. Public health experts are concerned that as vaccination lags and the Delta variant surges as fall approaches, hospitals could once again become overwhelmed and the death count could continue to grow significantly. Vaccines have not yet been approved for kids under the age of 12, putting them, their families, and school employees at risk of infection as the school year nears.