The government has ambitiously announced that, in the event of a smallpox attack, the population of the United States could be vaccinated within 10 days if necessary. But what about in advance of an attack? In recent months, there has been increasing commentary about the right of every American to decide whether to be vaccinated. But do we know enough to exercise such a right responsibly? And if we have a right to be vaccinated, pre-attack, are there circumstances under which we might also have a duty to do so?

If the government's coming program to vaccinate health care workers goes well, and a sufficient quantity of the vaccine is licensed (sometime in 2004), it seems likely that each of us will be allowed to decide whether we want to be vaccinated. But we need to be given a real choice. We need to be able to weigh our personal risk of death and disability from the vaccine against the likelihood that we could get vaccinated "in time" should the nation be attacked. Unlike many vaccines, the vaccine for smallpox offers immediate benefit. The government's post-attack vaccine plan is based on the premise that most of us could get vaccinated either before we became infected or early enough afterward for the vaccine still to be of use. For Americans to have a real choice, federal and local authorities must provide the public with credible information, not only about the personal risks of vaccination but also about the likelihood that the government could rapidly deliver vaccine to each of us after an attack.

In deciding whether to be vaccinated, we also need to weigh our personal risk of harm against the possibility that our being vaccinated may put others in harm's way. Vaccinated individuals can transmit the vaccine virus to people who are at increased risk of dying or suffering serious injury from the vaccine. These include people on chemotherapy; recent recipients of organ donations; people with autoimmune diseases, HIV and AIDS; people with skin disorders such as eczema and dermatitis; and very young children. Although the risk of secondhand transmission of the vaccine virus is likely to be quite low, if there is close contact, a recently vaccinated person does pose some threat.

Another consideration is the matter of simple justice. If, pre-attack, Americans are to decide for themselves whether to be vaccinated, surely this choice should be available to all of us. But who will pay for the vaccine? Should managed care be obligated to cover the costs? What about Medicare and Medicaid? And what about the uninsured? Who should cover the medical expenses that result from vaccine-related complications? Who should be legally responsible for any adverse reactions or secondary infections?

The answers to these questions depend in part on whether it is in the national interest for some of the general public to be vaccinated in advance of an outbreak. The more of us who are vaccinated, the greater the costs and the greater the toll from vaccine-related complications. As the toll mounts, the greater the possibility of a backlash against all immunizations, including basic childhood vaccines. This is why, unless the threat of a smallpox attack becomes more ominous, a mass vaccination campaign is not justified, even if permitting individual citizens to choose to be vaccinated is.

But what if the threat does become more ominous? The government might then have good reasons for mounting just such a public health campaign. If smallpox were to be unleashed and some of us were already protected, our ability to rapidly vaccinate those who should not be vaccinated before an attack might well improve. We might also buy some time; having a proportion of the population vaccinated could serve to slow the spread of the infection. And there is a possibility that having a partially vaccinated population would make smallpox a less attractive weapon, thus reducing the chance of an attack in the first place.

Making such trade-offs is not a matter of individual choice, however. It is a matter of national leadership. Should the government ever determine that mass vaccination before an attack is in the national interest, then some of us -- those who are not at increased risk of vaccine complications and who are unlikely to put others at risk -- may have not only a right to be vaccinated, but also a moral duty to do so. We should voluntarily assume the risks of vaccination, pre-attack, in order to protect those among us who are more vulnerable to the vaccine's risks. As a matter of fairness, however, the vaccine should then be free, as should medical treatment for any adverse reactions to it. And we will need to consider a national compensation program for those who suffer permanent disability and families of any who die.

Allowing Americans access to the vaccine before an attack does not in any respect lessen the urgency to create an infrastructure capable of distributing vaccine to huge numbers of Americans within 10 days if we are attacked. Upwards of 50 million Americans will be advised not to be vaccinated before an attack because of their susceptibility to vaccine complications. Many millions more, including close contacts of those at increased risk, may choose not to be vaccinated. Moreover, smallpox is not our only bioterrorist threat. We need an infrastructure capable of delivering whatever vaccine or treatment is indicated to all residents of this country in a matter of days. The debate over the right or the duty to be vaccinated must not be allowed to detract from what is absolutely essential to homeland defense and our personal security: the building of an effective emergency public health infrastructure.

The writer is director of the Berman Bioethics Institute at Johns Hopkins University. She will answer questions about this article in a Live Online discussion at 1 p.m. today on www.washingtonpost.com.