Smallpox vaccine - heart attack link unlikely, historical study suggests

Oct 6, 2003 (CIDRAP News) – New York City health records show no increase in cardiac deaths after a citywide smallpox vaccination campaign in 1947, which supports the view that cardiac events in 16 people vaccinated recently were unrelated to the vaccine, according to the Centers for Disease Control and Prevention (CDC).

The records were examined as part of the investigation triggered by ischemic cardiac events in the 16 military and civilian vaccinees, three of whom died, according to the Oct 3 issue of Morbidity and Mortality Weekly Report. The three people who died—two civilians and one military man—were all in their mid-50s and had several risk factors for heart disease. The deaths occurred between 4 and 17 days after vaccination.

About 6.4 million New York City residents—80% of the city's population—were vaccinated in April and May of 1947 in response to a smallpox outbreak. To detect any increase in cardiac, atherosclerotic, or all-cause deaths, New York City health officials recently examined death certificates dating from March through June of 1946, 1947, and 1948, according to the MMWR article. They focused on the 2-week and 4-week periods following the peak of the immunization campaign.

The investigators found 81,010 legible death certificates from the periods of interest. Forty-eight percent of the certificates listed cardiac disease as the cause of death, and 11% listed coronary artery or atherosclerotic disease specifically. Comparing cardiac death rates for the 2-week postimmunization period and other periods, the investigators found no significant differences. Similarly, they found no significant difference between the 4-week postimmunization period and other periods with regard to cardiac deaths or all-cause deaths.

"The findings are consistent with a growing body of evidence suggesting that ischemic cardiac deaths observed after the 2003 campaign might have been unrelated to vaccine," the report states. It says the same vaccinia strain (New York City Board of Health) was used in the 1947 vaccination campaign as in this year's campaign.

The article notes that nonfatal heart inflammation (myocarditis and/or periocarditis) has occurred in a number of recent smallpox vaccinees, but autopsies indicated that the three recent cardiac deaths were linked directly to ischemic events, not inflammation. Whereas evidence suggests that the inflammation cases were related to the vaccine, "few data support the association of ischemic cardiac adverse events with smallpox vaccination."

In the current immunization program involving military personnel and selected civilian health workers, the CDC uses screening guidelines designed to minimize cardiac risks by excluding people with heart disease or three or more cardiac risk factors. That precaution should be maintained even though this study casts doubt on the possible link between smallpox vaccine and fatal cardiac events, the report says.

CDC. Cardiac deaths after a mass smallpox vaccination campaign—New York City, 1947. MMWR 2003;52(39):933-6 [Full text]

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