As the Zika virus continues to sweep through Latin America and begins what appears to be a steady march into the United States, the hunt is on for a vaccine against it. In addition to posing scientific and medical challenges, the development of a Zika vaccine raises social and ethical issues with a twist because of what this vaccine will do and who it is aimed at. In some ways it will be like a vaccine developed almost 50 years ago to fight rubella, a virus that also attacked developing babies.

Infection with the Zika virus generally isn't a big deal. Most people don't develop any symptoms. Those who do may have a low-grade fever, skin rash, conjunctivitis, muscle or joint pain, or fatigue that disappears within a week. A small number of people infected with the Zika virus develop Guillain-Barré syndrome, in which the immune system attacks nerves, causing pain or partial paralysis.

Among women who are pregnant, though, infection with the Zika virus can have devastating consequences for their developing babies. These range from microcephaly, a condition characterized by a small head and impaired brain development, to seizures, vision and hearing loss, and intellectual disability.

To date, about 1,500 babies worldwide have been born with microcephaly from Zika exposure. The first Zika-affected baby in the U.S. was born in June. Hundreds of pregnant women have tested positive for Zika and are waiting to see if their babies are affected. A new outbreak in Florida this summer makes clear the stakes will continue to grow.

There are strong parallels between Zika and rubella, also known as German measles. An outbreak of rubella rocked the United States in the winter of 1964 and spring of 1965. More than 12 million people were infected with rubella. Like Zika, rubella is generally a minor illness. It causes a distinctive red rash, low fever, and symptoms resembling a bad cold that usually last a few days. For developing babies, however, infection can be a major catastrophe, causing a variety of birth defects, including blindness, deafness, heart damage, cataracts, internal organ damage, and intellectual disability. During that rubella outbreak, more than 20,000 babies were born with congenital rubella syndrome. Without a vaccine, there was nothing their mothers could have done to prevent it.

A vaccine against rubella became available in 1969. Since then, this disease has been eradicated in the United States. But it wasn't initially smooth sailing for the vaccine. The question of who should get it loomed large. Unlike other vaccines, which protect children and adults, the rubella vaccine aimed to protect fetuses, who can't be directly vaccinated. Giving the vaccine only to women who intended to become pregnant or to teenage girls wasn't successful in preventing congenital rubella syndrome given the high rate of unintended pregnancy and circulation of the virus among men and children with whom women of childbearing age came into contact.

Experts ultimately rejected a strategy of giving the vaccine to women whose fetuses would most directly and immediately benefit. They instead adopted the strategy of vaccinating all girls, some of whom would eventually become pregnant, and all boys, who would inevitably interact with pregnant women in the community.

Although exceedingly safe, the rubella vaccine can cause mild symptoms that last a few days. It occasionally causes more serious reactions. Yet the rarity of adverse reactions to the vaccine weighed against the widespread damage of congenital rubella syndrome led to a clear public policy mandate to vaccinate all children against it.

The rubella vaccine introduced the possibility that we could ask individuals to absorb a small risk of an adverse reaction to protect the most vulnerable members of the community: in this case, the unborn. In doing so, Americans defined a culture of shared responsibility and shared benefit.

The development of a Zika vaccine is still in its early stage. The Food and Drug Administration has granted a license to one company to conduct Phase 1 safety trials of a Zika vaccine on healthy volunteers. If it is successful, a larger-scale effort to develop a vaccine will take a large public investment.

If a Zika vaccine is developed, Americans will need to have a conversation about who should get it. Although a small number of those infected by the Zika virus experience severe neurological symptoms, the main thrust of the vaccine is to protect fetuses. As with rubella, Americans could accept a shared responsibility to protect the most vulnerable in our community, though the appetite for that appears to be waning.

In the 1960s, parental support for vaccination was high. Not so today, as I write in my recent book about vaccines. Parents are increasingly rejecting vaccinations that provide protection to the community and focusing on the risks and benefits to their own children, even as those decisions may place others at greater risk.

Finding the political and economic will to support a real public health intervention against Zika won't rest on individuals' calculations of benefit. Instead, it will require a different vision of what community means, one that sadly seems to belong to a bygone era.

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