NEW YORK (Reuters Health) - More than 33,400 U.S. health care workers have been given the smallpox vaccine, and of those, 45 have experienced serious side effects, according to a U.S. Centers for Disease Control and Prevention report released Thursday.

In one case, the CDC reports, a person vaccinating patients reinserted a used needle back into a vial and went on to vaccinate additional people from the contaminated vial.

As of April 18th, a total 10 people have experienced myopericarditis, an inflammation of the heart muscle or sac surrounding the heart, and six have had heart attacks after being vaccinated. However, it still is not clear if this was caused by the vaccine or was a coincidence, according to the CDC.

An additional 369 people have reported less serious side effects such as fever, rash, headache and pain, according to the CDC.

In March, the CDC changed the smallpox vaccine recommendation after three heart attack deaths in vaccinated individuals, including two health care workers and one National Guardsman.

Even though the cases were not definitively linked to the shot, the CDC recommended that anyone with a history of heart disease or those with three or more major risk factors for heart disease, such as hypertension, high cholesterol and smoking, be excluded from the vaccination program.

The virus used in the vaccine, vaccinia, is known to cause inflammation of the heart muscle and lining.

The CDC also emphasized the need for health care workers to follow proper infection-control procedures when giving the vaccine. Workers usually insert a sterile needle into a multidose vial, vaccinate an individual and then discard the needle.

In one incident, a health care worker put a used needle back into a vial, and then used the vial for later inoculations. Reinserting a dirty needle in a sterile vial of vaccine could increase the risk of transmitting bloodborne illnesses such as hepatitis and HIV, although the initial patient tested negative for HIV and hepatitis B and C virus.

"Vaccinees who receive potentially contaminated vaccine should be offered follow-up testing for infectious diseases of concern, if possible, based on knowledge of test results from the initial vaccinee," according to the report.

Other side effects seen after vaccination include eight cases of generalized vaccinia, a skin infection caused by the vaccine, and 29 instances of "inadvertent inoculation," in which a person unintentionally spreads vaccinia from the inoculation site to another region of the body, causing a rash or an outbreak of vaccinia sores. Some of those cases are under investigation and have not yet been confirmed.

Overall, 33,444 civilian health care workers have been inoculated since January, according to Thursday's Morbidity and Mortality Weekly Report.

The United States stopped routine smallpox vaccinations in 1972, but decided to resume them for select groups last year as fears grew that the virus could be used as a biological weapon.

Smallpox kills about 30 percent of its victims and scars the remainder for life. It was declared eradicated in 1979, but stores of the virus still exist.

When administered in the past, the vaccine killed one to two out of every million people inoculated. Some 52 out of every million became severely ill, including some who suffered brain damage. But it has never before been linked to heart problems.

SOURCE: Morbidity and Mortality Weekly Report 2003;52:360-363.

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