ATLANTA - The U.S. government announced Friday that it has said goodbye to one of the world's greatest lifesavers -- the oldest smallpox vaccine. The U.S. Centers for Disease Control and Prevention this month made arrangements to dispose of the last of its 12 million doses of Dryvax, and notified other health departments and the military to do the same by Feb. 29.
Dryvax -- produced by scraping virus off the skin of infected calves -- is being replaced in federal vaccine stockpiles by a more modern product manufactured in laboratories.
Dryvax was unusually dangerous for a vaccine, blamed in recent years for triggering heart attacks and a painful heart inflammation in some patients.
Still, attention should be paid on the occasion of its demise, said Dr. William Schaffner, chairman of Vanderbilt University's department of preventive medicine.
It is a "historical moment, because it's our oldest vaccine," Schaffner said. "It was a vaccine that eliminated smallpox from the United States."
Smallpox is a deadly, infectious disease that plagued the world for centuries and killed nearly a third of the people it infected. Victims suffered scorching fever and body aches, then spots and blisters that would leave survivors with pitted scars.
Dryvax was created in the late 1800s, by the company that became Wyeth Laboratories. Wyeth was a primary U.S. manufacturer of smallpox vaccine by the mid-1940s, and was the only company left making it by the early 1960s, said Dr. D.A. Henderson, a University of Pittsburgh vaccine expert who played a key role in international smallpox eradication efforts.
The United States was able to end routine childhood vaccination against the disease by the early 1970s. World health authorities declared the disease was eradicated from nature in 1980.
Wyeth stopped making the vaccine in the 1980s. But government officials kept a stockpile of about 15 million doses. The Dryvax came in handy in 2003, when it was used to help contain an outbreak of monkeypox in the United States.
"There are situations where one does have to have a smallpox vaccine," said Dr. Neal Halsey, director of John Hopkins University's Institute for Vaccine Safety.
U.S. officials had also been worried that smallpox might resurface as a result of bioterrorism. Following the 9/11 attacks and the anthrax-containing letters that surfaced a month later, the government in 2002 ordered certain military personnel vaccinated and recommended shots for front-line health care workers.
The government also pushed for manufacture of a new vaccine. It hired a company named Acambis Inc., which had produced nearly 200 million doses by the end of 2003, Henderson said.
Last September, the U.S. Food and Drug Administration approved licensure of the company's ACAM2000 vaccine. That product is now the mainstay of the CDC stockpile, Henderson said.
Dryvax had problems. It was long suspected of triggering neurological complications, including encephalitis, in rare cases. Then, in 2003, three adults who received the vaccine died suddenly of heart attacks. As a precaution, health officials advised people with heart disease to skip the vaccination.
A study published in 2005 suggested that Dryvax triggered a painful heart inflammation in a small number of emergency workers vaccinated after Sept. 11.
"Times had changed, and our awareness, sensitivity and tolerance for adverse events associated with vaccines was much greater" than during the smallpox vaccination campaigns of the 20th century, Schaffner said.
ACAM2000 is created in laboratories, not on a farm, so there's much less possibility of bacterial contamination in the production process. However, it's derived from Dryvax, and it's not clear it will have fewer side effects than the old vaccine, some vaccine experts said.
