ATLANTA — Following a walk through nearly empty hallways, there is no receptionist at Dr. Thomas Frieden's outer office. Just a ring-for-service sign. The director of the Centers for Disease Control and Prevention is trying to manage a partial shutdown at an institution where nearly everything is ultimately a matter of life or death. "The longer it goes," he says, "the more complex it is. What isn't an imminent threat to health on day four is on day 10."

As of now, eight of 10 global disease detection centers — the field offices where outbreaks are identified and countered — are closed. No processing of blood samples for parasitic diseases is taking place. No testing of counterfeit malaria medicines.

Fortunately, the CDC's polio eradication effort has been largely exempted from the shutdown. It is part of one of the most ambitious medical enterprises in history — attempting to eliminate a highly contagious virus from the wild. This has been achieved only twice before, with smallpox and rinderpest. The end of polio transmission is a few hundred yearly cases away. Even a brief pause would risk losing ground.

Poliovirus — which destroys neuron cells controlling swallowing, breathing and use of limbs — was once a source of seasonal panic in the United States. Epidemics (usually arriving in summer) sometimes caused states to close their borders, with inspectors demanding certificates of health from children under 16. American infections peaked at nearly 58,000 in 1952. (Sen. Mitch McConnell and Rep. Steve Cohen were both infected as children.) As late as 2004, dozens of Americans still lived in iron lungs.

But the use of the Salk and Sabin vaccines has chased the virus across the planet. The last American infections were in 1979 (among Amish who resisted vaccination). This was also the year that Rotary International started a campaign to eliminate polio transmission in the Philippines, beginning a global eradication movement that now includes the World Health Organization, UNICEF, the Gates Foundation and the CDC. In 1999, Type 2 poliovirus (of three types) was eliminated in the wild. India has been polio-free since 2011 — an important proof of concept. (If polio can be eliminated in northern India — with its dense population and poor sanitary conditions — it can be defeated anywhere.)

More than 99 percent of poliovirus transmission has been stopped over the last few decades. But the final bit is the hardest.

In 2011, an independent review panel questioned if the opportunity for polio eradication was being squandered. It lit a fire under the movement. Partners increased their commitments. Frieden moved his effort into the CDC's Emergency Operations Center — a high-tech amphitheater in which the disease is minutely tracked in maps and charts.

There are two regions where wild polio transmission has never been eradicated: in the tribal areas along the Afghanistan/Pakistan border and in northern Nigeria. In Afghanistan, efforts by the ministry of health have been innovative and successful. There have been only six cases so far this year, all of which (when the CDC examined the genetic fingerprints of the viruses) originated in Pakistan. In Pakistan, infections are largely confined to North Waziristan, where the local Taliban commander has banned vaccination. In Nigeria, the government has recently improved the management of its program and infections are down. But the terrorist group Boko Haram — which rejects everything Western, including vaccines and education — is suspected of being responsible for the murder earlier this year of nine polio workers. Polio is a killer that finds allies among killers.

Now a virus originating in Nigeria has caused an outbreak in Somalia, which has spread some cases to Kenya and Ethiopia. Health authorities in Mogadishu responded with surprisingly celerity, beginning immunizations four days after the first reported illness. But the problem persists in less populated areas controlled by al-Shabab. Somalia, which has ended polio transmission twice before, must do it a third time.

Polio eradication is an enterprise now conducted at the frontiers of medicine and war — introducing vaccination into places that have never seen Western medicine and sometimes requiring negotiations with warlords and militias. In some places, the challenge is management; in others, security. The complexity can be frustrating. "It is like finishing a marathon," one CDC expert told me, "and being told you have an extra mile to run."

But these are struggles near the finish line of a landmark scientific achievement. And for those who doubt that any purpose of government can be essential, the daring, humane work of the CDC is a corrective.

Michael Gerson's email address is