The Most Dangerous Vaccine

(CBS)  Smallpox may be the worst disease ever known to man -- it killed about half a billion people from 1880 to 1980, before it was eradicated. And the smallpox vaccine is deadly too -- scientists call it the most dangerous vaccine known to man.

Today smallpox is a potential weapon of mass destruction that could be wielded against the US by enemies like Iraq and al Qaeda. The Bush administration now faces a deadly dilemma: Do not vaccinate the population against small pox and leave millions of people vulnerable to one of the worst scourges known to man. Or treat people with a vaccine that is extremely effective at blocking the disease but can cause dangerous, sometimes fatal reactions. 60 Minutes II Correspondent Dan Rather reports on a story that puts everyone on the front lines in the war on terror.

Dr. Paul Offit is one of the country's top infectious disease specialists, and he knows all about vaccines that prevent those diseases. In his lab at Children's Hospital of Philadelphia, they study and create new, cutting-edge vaccines. But there's nothing new about the smallpox vaccine.

The vaccine was created in 1796. The vaccine used today is essentially the same, Offit says. "We tend to think of vaccines as being very safe and every effective, which they are. But all the vaccines that we use today are the result of modern technology. That's not true of the smallpox vaccine. It has a side effect profile that we, we would not accept for vaccines today," he says.

Smallpox is a contagious virus that has plagued mankind for thousands of years. It was eradicated in 1980. In the century before that, smallpox killed a half-billion people worldwide, and scarred hundreds of millions more.

The smallpox vaccine is made from a weak biological cousin of the smallpox virus. When you get vaccinated with the weaker virus, as millions of Americans were in the 20th century, you become immune to the very strong - and deadly - smallpox virus.

But once in a while, the vaccine does more harm than good. If you scratch where the smallpox is at the surface, and you put it to the eye, you can transfer the smallpox to your eye. That occurs in about 500 people for every million that get the vaccine. If you get 'progressive vaccinia.' your immune system is compromised, the virus continues to grow, and is often the cause of death.

No one is certain how many people will be hurt by the vaccine. A 1969 study found that, out of every one million people vaccinated, 74 will suffer serious complications, and at least one will die.