he Bush administration is sending out its first batches of smallpox vaccine this week so that health officials can begin immunizing health care workers against infection should there be a terrorist attack. Despite a small backlash against the vaccination campaign in medical circles, there is good reason to proceed with such immunizations promptly so that a cadre of health workers is available to treat the victims of any terrorist attack without its members falling sick themselves or spreading the disease to others. But medical experts have raised enough cautionary flags that the administration ought to consider modifications that could help the program achieve its goals with greater assurance of safety and effectiveness.

We think the administration's health officials are right to press ahead with the first phase of immunizations, aimed at up to 500,000 health workers throughout the country, despite calls for a slowdown by health unions and the prestigious Institute of Medicine. Nobody knows whether any terrorist group or rogue nation possesses a smallpox weapon, but if there is any danger it is most likely to erupt at a time when the United States is threatening to invade Iraq. The time to get ready for terrorism is now, not months from now.

Even so, there are elements of the vaccination campaign that should be modified. One critical missing element is compensation for medical expenses or lost income for any health workers who suffer serious side effects from the vaccine. The Homeland Security Act enacted last year grants compensation only for injuries resulting from negligent manufacture or administration of the vaccine, leaving individuals who get vaccinated to rely on their own health insurance or workmen's compensation laws that may not cover everyone.

Yet this is a vaccine that, even when perfectly made and administered, is expected to cause one or two deaths and 15 or more very serious complications in every million people vaccinated. The administration and Congress should work together to create a compensation fund, and any health workers who volunteer in the absence of such a fund should be warned that they may not be covered for injuries or lost pay.

The Institute of Medicine, part of the National Academy of Sciences, offered several useful recommendations last week for improving the program. Most important was a call for a pause after the first phase so that side effects can be analyzed carefully before embarking on the next phase, to vaccinate some 10 million health and emergency workers. That would allow prudent changes in the plan without greatly harming the readiness of the health system to respond to smallpox terrorism.