(CNN) Pope Francis suggested that contraceptives may be used to prevent the spread of the Zika virus, despite the church's longstanding ban on most forms of birth control.

His comments may cheer health officials in Latin America but are likely to upset conservative Catholics.

At a press conference aboard a flight from Mexico to Rome on Thursday, the Pope was asked whether the church should consider contraception the "lesser of two evils" compared with the possibility of women aborting fetuses infected with Zika. The virus has been linked to an incurable and often devastating neurological birth defect.

The Pope first answered by calling abortion an "absolute evil" and a "crime."

"It is to kill someone in order to save another. This is what the Mafia does," Francis said. "On the other hand, avoiding pregnancy is not an absolute evil."

The Pope then pointed to a narrow historical exception to the church's ban on most forms of birth control: A predecessor, Pope Paul VI, allowed African nuns to use contraceptives "in cases of rape," Francis said.

"In certain cases ... such as the one I mentioned of Blessed Paul VI, it was clear," the Pope said. Paul VI also wrote "Humanae Vitae," the papal document that solidified the church's stance against almost every form of birth control in 1968

Francis was likely referring to nuns in the Belgian Congo during the 1960s, who used anovulant, a form of contraception that prevents ovulation. They did so to avoid the possibility of becoming pregnant by rape, a threat during the country's political upheaval.

"There was a legitimation of contraception at the time, and I think he's saying that a similar situation now exists in countries where the Zika virus is prevalent," said the Rev. James Keenan, an expert on Catholic sexual ethics and morality.

Keenan said the Pope's comments, although made in an off-the-cuff interview and not an official papal document, could have broad implications for health care providers, not only in Latin America but also the United States and elsewhere.

"This is not just about individuals. This is about the thousands of Catholic hospitals that can help women in this situation" by providing contraception.

Keenan compared the Pope's comments to remarks made by his predecessor, Pope Emeritus Benedict XVI, in 2010. In a book-length interview, Benedict said that in some cases, using condoms to prevent the spread of disease could be the "first step" toward moral responsibility.

Francis' comments on Thursday take that argument several steps farther, Keenan said.

A fierce debate

Aline Kalbian, professor of religion at Florida State University who has studied the Catholic Church's contraception ban, said the Pope's comments on Thursday surprised her. They countered the dominant view of Vatican officials for decades: the church allowed no exceptions.

"He seems to be really clear that this is an exception and he's going to allow it."

The church does allow natural family planning, which involves a woman monitoring her basal body temperature and vaginal secretions to avoid having sex at fertile times of the month.

It's not entirely clear what the chances are that a pregnant woman who contracts Zika will have a baby with microcephaly. Babies with the defect have small heads and abnormal brain growth and often have developmental delays, seizures, problems with movement and speech and other issues.

On Thursday, the World Health Organization called for access to emergency contraception and counseling for women who "have had unprotected sex and do not wish to become pregnant because of concern with infection with Zika virus."

As in the United States, many Catholics in Latin America don't follow the church's advice on birth control anyway. According to a survey by the Spanish-language television network Univision, 88% of Mexicans, 91% of Colombians and 93% of Brazilians support the use of contraceptives.

But the Catholic catechism states that aside from natural family planning, anything that works to "'render procreation impossible' is intrinsically evil." The church's teachings have put women in Latin America, where a majority of people are Catholic, in a difficult situation.

In December, authorities in Brazil urged women not to get pregnant . Then last month came the warning from Colombia to delay pregnancy until July. Then in an interview, a health official in El Salvador recommended that women "try to avoid getting pregnant this year and the next."

The Rev. John Paris, a bioethicist and Catholic priest at Boston College, said Pope Francis is primarily a pastor, not a systematic theologian interested in abstract ideas. In contrast to previous popes, Francis formed his style of ministry in the slums of South America, not European seminaries.

Photos: Zika virus outbreak Photos: Zika virus outbreak A pest control worker fumigates a school corridor on the eve of the annual national Primary School Evaluation Test in Kuala Lumpur on Sunday, September 4. Malaysia reported its first locally transmitted Zika case on September 3. Hide Caption 1 of 29 Photos: Zika virus outbreak A banner about Zika virus is seen as ferry passengers arriving from Singapore get in line at the immigration check on September 4, in Batam, Indonesia. Hide Caption 2 of 29 Photos: Zika virus outbreak A banner is flown over the South Pointe Park area, Tuesday, September 6, in Miami Beach, Florida. Hide Caption 3 of 29 Photos: Zika virus outbreak A pest control worker fumigates drains at a local housing estate where the latest case of Zika infections were reported on Thursday, September 1, in Singapore. Hide Caption 4 of 29 Photos: Zika virus outbreak Florida Gov. Rick Scott and Florida Surgeon General Dr. Celeste Philip address the media gathered at the Miami-Dade County Department of Health as they announce five cases of Zika in a 1.5 mile area of Miami Beach on Friday, August 19, in Miami, Florida. Hide Caption 5 of 29 Photos: Zika virus outbreak Brazil's interim President Michel Temer, center right, meets with officials during Temer's first visit to the Olympic Park on Thursday, June 14, in Rio de Janeiro. The Rio 2016 Olympic Games commence August 5 amid a political and economic crisis in the country along with the Zika virus outbreak. Hide Caption 6 of 29 Photos: Zika virus outbreak Rio 2016 Chief Medical Officer Joao Grangeiro, Municipal Secretary of Health Daniel Soranz and Sub-secretary of the State for Health and Surveillence Alexandre Chieppe field questions from the media during an International Media Briefing to address the Zika virus on Tuesday, June 7, in Rio de Janeiro. Hide Caption 7 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Gama, Brazil, to combat the Aedes aegypti mosquito on Wednesday, February 17. The mosquito carries the Zika virus, which has suspected links to birth defects in newborn children. The World Health Organization expects the Zika outbreak to spread to almost every country in the Americas. Hide Caption 8 of 29 Photos: Zika virus outbreak A man places a mosquito net over a bed at a home for the elderly in Masaya, Nicaragua, on Thursday, February 11. Hide Caption 9 of 29 Photos: Zika virus outbreak An Aedes aegypti mosquito floats in stagnant water inside a tire at a used tire store in Villavicencio, Colombia, on Thursday, February 4. Hide Caption 10 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Caracas, Venezuela, on Tuesday, February 2. Hide Caption 11 of 29 Photos: Zika virus outbreak A lab worker exposes his arm to Aedes aegypti mosquitoes during testing at the Roosevelt Hospital in Guatemala City, Guatemala, on Monday, February 1. Hide Caption 12 of 29 Photos: Zika virus outbreak Tainara Lourenco sits inside her home in Recife, Brazil, on Friday, January 29. Lourenco, five months pregnant, lives at the epicenter of Brazil's Zika outbreak. The Zika virus has been linked to microcephaly, a neurological disorder that results in newborns with small heads and abnormal brain development. Hide Caption 13 of 29 Photos: Zika virus outbreak Dr. Angela Rocha shows brain scans of a baby born with microcephaly at the Oswaldo Cruz Hospital in Recife on Thursday, January 28. Hide Caption 14 of 29 Photos: Zika virus outbreak Alice Vitoria Gomes Bezerra, a 3-month-old baby with microcephaly, is placed in her crib by her father Wednesday, January 27, in Recife. Hide Caption 15 of 29 Photos: Zika virus outbreak A health ministry employee fumigates a home in Soyapango, El Salvador, on January 27. Hide Caption 16 of 29 Photos: Zika virus outbreak A lab technician at the Oswaldo Cruz Foundation Institute stores Aedes aegypti mosquitoes to be used in research in Recife on January 27. Hide Caption 17 of 29 Photos: Zika virus outbreak A patient suffering from Guillain-Barre syndrome recovers at a hospital in San Salvador, El Salvador, on January 27. Researchers are looking into a possible link between Zika and Guillain-Barre, a rare disorder that causes the body's immune system to attack its nerves. Hide Caption 18 of 29 Photos: Zika virus outbreak Luiz Felipe lives in Recife and is one of more than 4,000 babies in Brazil born with microcephaly since October. The drought-stricken impoverished state of Pernambuco has been the hardest-hit, registering 33% of recent cases. Hide Caption 19 of 29 Photos: Zika virus outbreak A health worker sprays insecticide under the bleachers of Rio de Janeiro's Sambadrome on Tuesday, January 26. Hide Caption 20 of 29 Photos: Zika virus outbreak A Brazilian soldier inspects a home in Recife on Monday, January 25, while canvassing the neighborhood and attempting to eradicate the larvae of mosquitoes linked to the virus. Hide Caption 21 of 29 Photos: Zika virus outbreak David Henrique Ferreira, a 5-month-old who has microcephaly, is watched by his brother in Recife on January 25. Hide Caption 22 of 29 Photos: Zika virus outbreak The larvae of Aedes aegypti mosquitoes are photographed in a lab in Cali, Colombia, on January 25. Scientists are studying the mosquitoes to control their reproduction and resistance to insecticides. Hide Caption 23 of 29 Photos: Zika virus outbreak Angelica Prato, a pregnant woman infected by the Zika virus, receives medical attention at a hospital in Cucuta, Colombia, on January 25. Hide Caption 24 of 29 Photos: Zika virus outbreak A woman walks through fumes as health ministry employees fumigate an area in Soyapango on Thursday, January 21. Hide Caption 25 of 29 Photos: Zika virus outbreak Brazilian soldiers apply insect repellent as they prepare for a cleanup operation in Sao Paulo on Wednesday, January 20. Hide Caption 26 of 29 Photos: Zika virus outbreak A researcher at the University of Sao Paulo holds a container with female Aedes aegypti mosquitoes on Monday, January 18. Hide Caption 27 of 29 Photos: Zika virus outbreak A graveyard in Lima, Peru, is fumigated on Friday, January 15. Hide Caption 28 of 29 Photos: Zika virus outbreak Aedes aegypti mosquitos are seen at the University of Sao Paulo on January 8. Researchers from the Pasteur Institute in Dakar, Senegal, came to Brazil to train local researchers to combat the Zika virus epidemic. Hide Caption 29 of 29

"He's a pastor and he's concerned with the plight of people in all their human dimensions," Paris. "And Zika is a problem that's suddenly confronting the world and just to repeat past abstract theories doesn't help resolve the question."

But the Pope's comments appear to put him at odds with some Catholic leaders in Latin America.

"Contraceptives are not a solution," Bishop Leonardo Ulrich Steiner, the secretary general of the National Council of Bishops of Brazil, said in an interview earlier this month. "There is not a single change in the church's position."

And a Catholic priest in Salvador told Catholic News Service that "If someone asks me for advice, I would say that the important thing is to get rid of the larvae, but I can't say do not get pregnant."

The Rev. Frank Pavone, national director of Priests for Life, has said that birth control is wrong , no matter what. "That prohibition doesn't change based on circumstances," he said. "So couples have a responsibility to live according to the church's teachings in whatever circumstances they find themselves."

The practical effect of papal comments

Will the Pope's remarks on Thursday really matter?

"I don't know that it will," Kalbian said. "Most Catholics have ignored Vatican teachings on this particular issue."

She said the Catholic Church teaches that every act of intercourse should be open to conception.

If the Pope is now saying it's acceptable not to be open to conception in the Zika situation, what other situations would it be okay to be not open to conception?

For example, if pregnancy could threaten the life of the mother, is it okay to use birth control? What if a couple is at an increased risk of having a baby with some genetic defect?

"I think they're going to have to answer these questions," Kalbian said of the Vatican.