In a technical sense it was true that the exiting 184 year-old (in 1980) vaccine did have too high risk of complications given the lack of smallpox in the wild. There are complications including encephalitis, and even death. Although these occur at low levels, innoculating everyone in a population in order to protect against an extinct disease will produce a number of injured people. The solution should be to develop new vaccines that are safer than the existing live vaccina vaccine. The technology for vaccines has improved greatly since 1796 when Jenner introduced vaccination.
An example of the tradeoffs between risks and benefits of different vaccines for one disease are the two vaccines for polio. The first vaccine (1955) was the killed Salk vaccine. The second (1961) was attenuated live Sabin vaccine. There was a vicious academic debate about which vaccine is safer or effective. It is often said that academic politics are viscious because the stakes are so low but in this case, the stakes were extremely high. Theoretically the killed vaccine should not cause the disease, but an early batch made by a licensee who did not completely follow Dr. Salk's protocol for killing the virus, caused an outbreak. The Sabin vaccine was tested in Africa with the assistance of the Soviet Union. There were some serious questions about the methodology of the study. The Soviets did not count any case of polio contracted less than 14 days after receiving the vaccine as being caused by the vaccine. Dr. Sabin was awarded the Nobel prize for medicine, but Dr. Salk did not share in it.
It was believed that the live oral vaccine is more effective in creating a life long immunity to polio. It is cheaper to manufacture, acts faster, and also has the ability to secondarily innoculate others who may come into contact with feces or water cominated by the feces of the recipient. Because of the ability to spread the effect of the vaccine beyond the person being inoculated, it was believed to be better for stopping outbreaks especially in less developed countries. The major problem is that about once in every 2.4 million cases the virus reverts back to pathogenic form and causes polio in the recipient. It also can cause the disease in others who may come in contact with the feces of the recipient. The last case of wild polio in the US occurred in 1979. After the 1980s almost every case of polio in the US was caused by the live vaccine; the others were aquired outside the US. There were several lawsuits in the 1980s and the protocols were changed so that the first two doses would be the inactivated or killed vaccine followed by two doses of the live vaccine.
The CDC's website says that the new protocol for 2000 is for four doses of an improved inactivated vaccine. The purpose of of this protocol is to totally eliminate the possibility of vaccine-caused polio. This is especially important since the wild virus does not exist in this country! The WHO is now in the process of eradicating polio from the world!
There are two major points I want to make about this digression about polio. First the safety of a vaccine for an extinct disease or at least extinct in this country has to be much higher than for a disease that is endemic or epidemic. Second, if a disease is eradicated in the wild, there is absolutely no way to verify that there are no undocumented samples of that disease in a laboratory. If we stop vaccinating, then future generations will become vulnerable to the use of polio as a biolgical weapon. I doubt very seriously after this scare about smallpox that citizens of the US would let the WHO and CDC stop the manufacture of polio vaccine when polio is eradicated in the wild. The WHO hopes to eradicate other diseases such as measles. This is a great thing for humanity, but we should never again make our population vulnerable to extinct diseases that could be used as biological weapons. We need to have research into producing vaccines that are much safer than the currently availabe ones for diseases that are targeted for extinction. This way we can justify vaccinating almost all the population against these diseases. If the overwhelming majority of people in this country and other highly developed countries were immune to smallpox, there would be no incentive for terrorists to use it.