The Food and Drug Administration has approved a new smallpox vaccine, ACAM2000, for active immunization against smallpox in individuals determined to be at high risk for smallpox infection. The vaccine also could be used to immunize populations during a bioterrorist attack.
Many doses of the vaccine will be stored in the Centers for Disease Control and Prevention's Strategic National Stockpile of medical supplies. The vaccine manufacturer, Acambis Inc., of Cambridge, England, and Cambridge, Mass., so far has supplied 192.5 million doses of ACAM2000 to the stockpile, according to the company.
The single-dose vaccine is approved under licensing that requires providers of the vaccine and patients to be educated about the risks of the virus through a Risk Minimization Action Plan. Patient education is supposed to be conducted through an FDA-approved medication guide, which describes the proper care of the vaccination site and the serious side effects that can occur.
Dryvax, the only other smallpox vaccine that is licensed by the FDA, was approved in 1931 and is now in limited supply because it is no longer manufactured. Dryvax was used to create ACAM2000, which is made using a live poxvirus called vaccinia. Vaccinia is related to, but different from, the virus that causes smallpox, and works by causing a mild infection that stimulates an immune response that will protect against smallpox, according to the FDA.
In one clinical study of ACAM2000, investigators found that the percentage of successful immunization reactions was similar for both ACAM2000 (96%) and Dryvax (99%) in patients who had never been vaccinated for smallpox prior to the trial.
Another study showed that ACAM2000 worked as successfully as Dryvax as a booster for those who previously had been vaccinated for smallpox (84% vs. 98%, respectively).
Cases of suspected myocarditis and/or pericarditis developed in 0.6% to 1% of all vaccinia-naive patients who received either ACAM2000 or Dryvax. Overall, 10 patients developed suspected myocarditis/pericarditis, which occurred at a mean of 11 days after vaccination with either vaccine. Only two of these patients required hospitalization. Eight of the cases were not detected until abnormalities were found on ECG. All patients had recovered by 9 months except for one, who had a persistent borderline abnormal left ventricular ejection fraction, according to the product label.
No cardiovascular inflammation or swelling occurred in previously vaccinated patients.
Patients who are vaccinated with ACAM2000 have to take precautions to prevent the virus from spreading from the inoculation site to other parts of the body and to other individuals, according to the vaccine's label.