A series of measles outbreaks all over the country in recent weeks have drawn scrutiny to parents’ decisions not to vaccinate their children. Before 2009, the measles vaccine was available as a stand-alone injection for parents who preferred it; this allowed parents to vaccinate their children against measles without using the rubella vaccine they view as problematic. Today the measles vaccine is available in the U.S. only bundled with the measles and mumps vaccines. Some anti-abortion groups blame the manufacturer, Merck, for failure to make an alternative available. “The onus on this should be the drug manufacturer and the FDA, not on the parents,” said Jill Stanek, an anti-abortion activist who has written frequently on the topic. An online petition posted in January urging Merck to revive the single-dose approach has garnered 1,780 signatures so far. The company has said there is no medical reason to administer the doses separately.

Hoekstra, who lives in an affluent suburb of Chicago, grew up in a household skeptical of vaccines. Her moral concerns and worries about the health consequences of her children receiving too many vaccinations in a short time — the Centers for Disease Control and Prevention recommends 10 vaccinations for children before they are 18 months — only grew as she began to read on the topic. Neither of her children have received any vaccinations yet, though she plans to start them on a limited and spaced-out schedule by age 3 or 4. She knows that rubella in particular is a serious disease, but given her ethical qualms, she hasn’t yet decided whether to include the measles-mumps-rubella vaccine in the schedule. “In some ways I feel like, if those precious babies had to die, maybe now they’re in some way saving lives,” she said. “But I don’t know if that sits well with me.”

“I think it’s something that needs to be honored and respected and discussed a little more openly,” said Joellyn Hoekstra, a surgical nurse and mother of two children under 3. “It’s not just a little small thing that no one needs to know. It feels deceiving, and it feels off to me.”

Maiorano is referring to a fact that rarely generates discussion — let alone concern — outside strongly anti-abortion circles. Several vaccines, including those used in the United States against rubella and chicken pox, are derived from cell lines originally obtained from two fetuses aborted in the 1960s. Fetal tissue is not present in the vaccines, and manufacturing the vaccines does not require an ongoing supply of fetuses. Yet among some anti-abortion parents, a deep moral wariness about using those vaccines persists.

“For me, the biggest issue was the pro-life issue,” she said. “If there was an act of taking a life that created this … I have a hard time accepting that, having it injected into myself and especially into my children.”

Heather Maiorano, a mother of two boys who lives in southern Oregon, has serious doubts about certain vaccinations. She and her husband have immunized their sons against what they perceive to be the most threatening diseases but have opted out of several others they see as less risky or less likely to be contracted. Unlike parents who worry about discredited links to autism , Maiorano has no major medical fears about vaccines. Instead her concerns are moral.

‘Abortion is an ongoing atrocity, and much medical research is still carried out using cells from aborted babies, so this moral problem is by no means limited to the past.’

It’s not only religious people who have qualms about the sources of these vaccines, although they are certainly driving the current conversation. In 2013 the scientific journal Nature published an editorial questioning the ethics of the origins of the cell line used in the rubella vaccine. It is not known whether the pregnant woman gave her consent for scientists to use the tissue, and it is unlikely she was compensated.

Although the abortions that led to these vaccines took place decades ago, many anti-abortion parents are not comforted by that distance. Deirdre Folley, a Catholic stay-at-home mother in New Hampshire, refers to them as “tainted vaccines” and is troubled by the idea of benefiting from what she views as a deeply immoral act. “Why should our health be predicated upon an innocent person's death?” she wrote in an email. “Abortion is an ongoing atrocity, and much medical research is still carried out using cells from aborted babies, so this moral problem is by no means limited to the past.”

Like many anti-abortion vaccine skeptics, Folley has relied on information from Children of God for Life, a nonprofit activist group that has been at the forefront of calling attention to the issue. It was a query from the organization more than a decade ago that prompted the Catholic Church to issue a statement reassuring parents that it is morally permissible to vaccinate in order to prevent the spread of disease, particularly rubella. (The statement acknowledged that parents who choose to vaccinate participate in a “very remote mediate material cooperation” with the abortions and encouraged them to lobby for alternatives.) Children of God for Life’s founder also sits on the board of Sound Choice Pharmaceutical Institute, a Seattle-based group that promotes the notion that fetal-cell-derived vaccines in particular are linked to autism.

All but two states allow vaccine exemptions for religious reasons. Although many if not all anti-abortion vaccine skeptics cite their faith as a factor in their reasoning, no major religious denominations have warned against vaccinations. In fact, some have directly urged followers to vaccinate their children. The country’s largest Protestant denomination, the Southern Baptist Convention, has published several recent articles online addressing the abortion link and reassuring believers that the vaccines are not just morally acceptable but are “inherently pro-life.”

Thomas Benton, a pediatrician in Gainesville, Florida, describes himself as Christian, anti-abortion and pro-vaccine. He is a member of the Christian Medical and Dental Organization, which has issued articles and more formal statements walking parents through the moral dimension of fetal-cell-derived vaccines. When asked if the trend toward vaccine skepticism worries him, Benton referred to a Bible verse that begins, “Be anxious for nothing.” But he said he encourages parents to vaccinate their children. “Just because something bad has happened doesn’t mean you shouldn’t move forward,” he said. “If you receive the measles vaccine or chicken pox vaccine or the hepatitis A vaccine and thus avoid a life-threatening illness, that’s a way of saving life. If you don’t get the vaccine and get one of these diseases and spread it, you might survive, but you might spread a life-ending disease to someone else.”

Mainstream medical and scientific consensus is that the vaccines are lifesaving and that not getting children vaccinated puts other people at risk by weakening herd immunity. "Vaccines today are very safe. They’re safer than the diseases they’re designed to prevent,” said Douglas Diekema, a pediatrician and director of education at the Treuman Katz Center for Pediatric Bioethics at Seattle Children’s Hospital, who pointed out that measles kills or disables 1 in 1,000 people who contract it. “When you’re going to school with others, I quite honestly think there is a moral duty to vaccinate your child.”

Many anti-abortion vaccine skeptics are keenly aware of this tension. For Maiorano, all she can do is make each decision as it comes. “As a pro-life person of faith, is it more pro-life to abstain from the vaccine or more pro-life to save your child from a life-threatening disease?” she said. In each case, “We went with what we thought was the lesser evil.”