CDC retires one old smallpox vaccine, keeps another

Mar 7, 2008 (CIDRAP News) – Federal health officials recently announced plans to get rid of their last remaining stocks of the decades-old smallpox vaccine Dryvax, as a newer vaccine takes its place in the national stockpile of emergency medical supplies.

Dryvax, which was made by Wyeth Pharmaceuticals and whose active ingredient is vaccinia virus grown on the skin of calves, is being replaced by ACAM2000, made by Acambis and grown in laboratory cell cultures. However, the national stockpile still contains, as a backup, hundreds of millions of doses of another old smallpox vaccine similar to Dryvax, according to the Centers for Disease Control and Prevention (CDC).

The CDC recently removed the last 7 million doses of Dryvax from the Strategic National Stockpile (SNS), CDC spokesman Von Roebuck told CIDRAP News. Wyeth intends to withdraw the Dryvax license and recently asked that all remaining doses be set aside for disposal, the CDC reported last week.

As of Feb 11, the SNS contained 195.2 million doses of ACAM2000 and 425 million doses of an older smallpox vaccine made by Aventis Pasteur (now Sanofi Pasteur), Roebuck reported. The Aventis vaccine was made before smallpox vaccination in the United States ended in the early 1970s, according to online information from the Food and Drug Administration (FDA).

ACAM2000, which is derived from Dryvax, was licensed by the FDA in August 2007. The Aventis vaccine was approved until 1997, when the manufacturer asked for revocation of the license, since routine vaccination had ended decades before, according to the FDA. But the product could be used in an emergency under the "investigational new drug" (IND) process.

"The AP [Aventis Pasteur vaccine] is in the SNS for use as an investigative new drug but is approved for use in an emergency," Roebuck said via e-mail. "We would use the licensed ACAM2000 first, then move to the AP in an outbreak."

Vaccine buildup began in 2000
Smallpox was eradicated in the 1970s, but the Soviet Union made large amounts of the virus in its Cold War biological weapons program. Public health experts have been concerned for years that terrorists might obtain a supply of the virus and try to use it as a weapon.

Impelled by these concerns, the CDC in September 2000 awarded Acambis a contract to make 40 million doses of its second-generation smallpox vaccine, to add to the 15 million doses of Dryvax the agency still had at the time. After Sep 11 and the subsequent anthrax attacks, the government ordered another 155 million doses from Acambis.

In May 2002 Aventis Pasteur revealed it had between 75 million and 90 million doses of smallpox vaccine in storage and was turning the whole amount over to the government. Later that year, Health and Human Services (HHS) Secretary Tommy Thompson said the Aventis vaccine totaled 85 million doses and could be diluted to yield five to ten times as many.

Dryvax has been used by the Department of Defense (DoD) to vaccinate more than 1.4 million military personnel since late 2002. Last month the DoD announced it was switching to ACAM2000. The vaccine is required mainly for personnel who serve in the Middle East and South Korea.

In addition to the DoD program, Dryvax was used in an HHS campaign in 2003 that aimed to vaccinate 450,000 healthcare workers because of the perceived threat of a biological attack. But health workers had concerns about the vaccine's safety and questioned the seriousness of the threat, and the effort largely fizzled, reaching only about 38,000 workers in its first 7 months.

The vaccine was also given to a few people who had potential exposure to monkeypox in the US outbreak in the summer of 2003. About 70 people contracted the illness after it spread to the United States via Gambian giant rats imported from Africa.

Deadline for destroying vaccine
In the Feb 29 Morbidity and Mortality Weekly Report, the CDC announced Wyeth's intention to withdraw the Dryvax license. "This withdrawal is not necessitated by any safety, purity, or quality concerns with the product but rather is consistent with a contract agreement between CDC and Wyeth," the notice said.

The CDC said all programs that have Dryvax supplies, such as state health departments and the military, must present the CDC with documentation of the vaccine's destruction by Mar 31. The agency said it would provide ACAM2000 to states for use by responders in public health emergency preparedness programs and by laboratory workers who risk exposure to orthopoxviruses.

Kris Ehresmann, RN, MPH, manager of immunization for the Minnesota Department of Health (MDH) in St. Paul, said the MDH has some doses of Dryvax left over from the 2003 vaccination effort and would be destroying them. She said other states may also have some leftover doses.

"We got the vaccine for the vaccination process [in 2003] and then we were able to store it, and the CDC continued to send updates about extending the shelf life," she said, adding that other states may have done the same.

Ehresmann said the MDH currently has no ACAM2000, but the department may ask the CDC for some doses for use by laboratory workers.

Similar safety profiles
Although ACAM2000 is produced with modern cell culture technology instead of the antique method involving calves, clinical studies have shown that the new and old vaccines have similar safety profiles, DoD officials said when they announced the switch to ACAM2000. The vaccines can cause swollen lymph nodes, sore arm, fever, headache, body aches, a mild rash, and fatigue.

Inflammation of the heart muscle and lining (myopericarditis) occurs in about 1 in 175 first-time smallpox vaccine recipients, according to the FDA. A DoD safety summary says 140 cases had occurred in the military vaccination program as of last May. Smallpox vaccination can also cause several other serious adverse reactions in rare cases, including localized or systemic spread of the vaccinia virus (eczema vaccinatum) and encephalitis.

In June 2007 US officials awarded a $500 million contract to Bavarian Nordic A/S for 20 million doses of a smallpox vaccine that is expected to be safer for people with weakened immune systems. The vaccine uses a weakened form of the vaccinia virus.

See also:

Feb 8 CIDRAP News story "US military switching to new smallpox vaccine"

May 29, 2002, CIDRAP News story "Aventis to give millions of smallpox vaccine doses to US government"

Nov 29, 2001, CIDRAP News story on Acambis contract to supply vaccine to HHS

This week's top reads