(CNN) -- As officials and health experts race to get Americans vaccinated against Covid-19, some Catholic bishops have weighed in to discourage Church members from getting the latest, single-shot vaccine from Johnson & Johnson when alternatives are available.
The US Conference of Catholic Bishops, as well as at least 6 other dioceses from across the country have released statements expressing "moral concerns" over the shot due to its use of lab-grown cells that descend from cells taken in the 1980s from the tissue of aborted fetuses.
The vaccine is the third to be authorized for use in the United States. Unlike its predecessors -- from Pfizer/BioNTech and Moderna -- the Johnson & Johnson vaccine requires only one shot and can be kept at normal refrigerator temperatures, making it easy to transport.
Health experts have cautioned that Americans should get the vaccine they are offered.
"If people are offered the Johnson & Johnson vaccine, they shouldn't say, 'I don't want it,'" Dr. Paul Goepfert, director of the Alabama Vaccine Research Clinic, said last month. "We are not in a scenario where we can pick and choose vaccines."
Prior to the US emergency use authorization for the Johnson & Johnson vaccine, the doctrinal office for the Roman Catholic Church -- the Congregation for the Doctrine of the Faith -- said that "it is morally acceptable to receive Covid-19 vaccines that have used cell lines from aborted fetuses in their research and production process."
The new statement from the Conference of Bishops is at odds with a note approved by Pope Francis, who received a vaccine in January. The December note said that "the use of such vaccines does not constitute formal cooperation with the abortion from which the cells used in production of the vaccines derive."
In a statement to CNN, Johnson & Johnson said: "We are proud to bring our COVID-19 vaccine to the world and to contribute to ending this pandemic. Our single-shot COVID-19 vaccine uses an inactivated non-infective adenovirus vector -- similar to a cold virus -- that codes for the coronavirus "spike" (S) protein, and there is no fetal tissue in the vaccine.
"We are able to manufacture hundreds of millions of doses using our engineered cell-line system and look forward to delivering those doses around the world and help meet the critical need."
The White House on Wednesday pushed back on the statement from the Conference of Bishops.
An administration official pointed CNN toward the Vatican statement from December, adding that the Biden administration is also "addressing hesitancy and working with local messengers on how to address that, including with religious leaders."
President Joe Biden is a practicing Catholic.
Making a vaccine with cells descended from fetal tissue
Vaccine makers sometimes use fetal cell lines when developing a vaccine.
Pfizer/BioNTech and Moderna used cell lines originating from fetal tissue to test their vaccines, whereas they were used in Johnson & Johnson's "development, confirmation and production,"according to Dr. James Lawler, an infectious disease expert at Nebraska Medicine.
Those cells are thousands of generations removed from the original fetal tissue, said Lawler.
Along with the use of cells, Johnson & Johnson's vaccine is made differently than the other two authorized vaccines.
The company developed an adenovirus vector vaccine, in which the adenovirus -- which has been modified to not cause illness -- carries genetic material with a coronavirus spike protein into a body so a person's cells can make the spike protein itself and activate their immune system against the virus, Lawler said.
Johnson & Johnson used the fetal cell line that it did because it is "a well-studied industry standard for safe and reliable production of viral vector vaccines," Lawler said.
What bishops are saying about the vaccine
But now, statements from US bishops are encouraging Catholics to opt to receive the Pfizer/BioNTec or Moderna option when possible.
The Archdiocese of New Orleans called the Johnson & Johnson vaccine "morally compromised" in a statement last week, and the dioceses of Baton Rouge, New Orleans and Burlington, Vermont, have released statements expressing concerns over the shot.
Bishop Michael Duca from the Baton Rouge Diocese released a statement that reads, "If for any reasonable circumstance you are only able to receive the vaccine from Johnson and Johnson, you should feel free to do so for your safety and for the common good."
The statement, which was echoed in Burlington, went on to say that the decision to receive the vaccine is between an individual conscience and their health care provider, but that "in no way does the Church's position diminish the wrongdoing of those who decided to use cell lines from abortions to make vaccines."
While Pfizer and Moderna vaccines should be chosen over Johnson and Johnson's where possible, the US Conference of Catholic Bishops said in a statement Tuesday it is "morally acceptable" to receive vaccines when "ethically irreproachable" options are not available.
"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," the statement said.
The statement was an update to one released in December that echoed the Vatican's statement, saying that Pfizer and Moderna vaccines were morally acceptable despite their "remote connection to morally compromised cell lines" due to the gravity of the pandemic.
What health experts are saying
Many health experts are encouraging those to whom the Johnson & Johnson vaccine is available to take it.
"My advice to all my patients and to all my friends will be to get the first vaccine you can get. That's what matters the most -- to get protected," said Dr. Jeff Carson, Provost at Rutgers Biomedical and Health Sciences of Rutgers University in New Jersey.
Dr. Anthony Fauci, the nation's top infectious disease expert who was raised Catholic, on Sunday urged Americans to take any of the three "highly efficacious" coronavirus vaccines now available to them and not delay getting one vaccine over another.
Americans generally haven't been offered a choice on which vaccine to get, although that may shift in some places as supply increases.
With the Moderna and Pfizer vaccines, some sites have been offering whatever vaccine they have the most of that day. The supply changes from week to week.
And though Pfizer and Moderna options boast an efficacy of about 95% compared to Johnson & Johnson's 72% in the US, experts say it is not the inferior option.
They say the Johnson & Johnson vaccine is an effective vaccine that offers good protection against severe forms of Covid-19. Anyone should take it if given the opportunity. The vaccine's efficacy goes up to 86% against severe forms of the illness.
"If we could prevent people completely from dying or getting hospitalized with Covid, we don't have a problem anymore," Goepfert said.
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