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Vaccinated people can transmit vaccinia virus

New research on smallpox vaccinations

By Gina Hill

New research on smallpox vaccinations

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Would you get a smallpox vaccination if one was available to you?

Not now, but maybe in the future

(CNN) -- Experts poring over data from past widespread smallpox vaccinations conclude the live virus used in the vaccine may result in cases of contact vaccinia -- the spreading of the vaccinia virus from someone recently vaccinated to someone who has not had the shot.

Vaccinia, a less virulent relative of smallpox, is the live virus used in smallpox vaccinations. People with skin disorders like eczema can spread the virus across their own skin and potentially infect others who aren't vaccinated. The vaccinia virus may cause a rash, fever and head or body aches.

The researchers, led by Dr. John Neff, a former researcher with the Center for Disease Control and Prevention's Smallpox Eradication Program, discussed what they found in a commentary in this week's Journal of the American Medical Association released today.

Their research focused on mass vaccinations in the United States, United Kingdom and Sweden from 1947 to 1968. Overall, in the U.S. studies, the rate of contact vaccinia was in the range of 2 to 6 per 100,000 vaccinations.

The majority of cases a few of which resulted in death -- occurred in children with eczema, a skin disorder characterized by itchy red skin and even blisters in severe cases. And the disease was more likely to be spread to people with a history of eczema even though they had no active skin lesions.

Age distribution of those U.S. cases shows young people are more vulnerable to contact vaccinia:

  • Younger than 1 year: 25 cases
  • One to 4 years of age: 113 cases
  • Five to 19 years of age: 40 cases
  • Twenty years or older: 44 cases
  • That translates to 62 percent of the cases occurring in children 5 years old or younger and almost 20 percent in those 20 years or older, according to the study.

    Most cases happened in the home, with many victims getting the virus from vaccinated family members or playmates. In rare cases, transmission occurred from a vaccinated nurse to a patient.

    "The risk (of contact vaccinia) is not large," the researchers write. "This risk needs to be kept in perspective."

    But they do admit that in this day and age we're more susceptible than past generations. Why?

  • Since widespread smallpox vaccinations stopped in 1972, almost everyone born since then has no immunity to vaccinia, according to the authors. If vaccinated, this group could spread the virus for up to 19 days. Even those who have had a smallpox shot in the past could shed more of the virus and for a longer period of time depending on how long it's been since their last vaccination and how many shots they've had in all. In short, most people born before 1972 have had only one smallpox shot and they would probably react as if they've never had one at all.
  • Eczema also called atopic dermatitis is more prevalent today. In the United States, rates have increased from 3 percent to 6 percent to 6 to 22 percent in the past 30 years, according to the researchers.
  • Today there are more people with weak immune systems. The authors theorize that's likely due to the spread of HIV and wider use of drugs to suppress the immune system for cancer patients and organ transplant recipients, for example. "Contact vaccinia in this population could be especially serious," the authors write.
  • Preparation and a carefully crafted vaccine policy is key to keeping contact vaccinia under control should mass smallpox vaccinations become a reality, according to the commentary.

    They recommend public health officials carefully screen for those with a history of eczema and compromised immune systems. The public should be informed about how contact vaccinia is spread and how to avoid it. Finally, a surveillance system needs to be in place to document and track adverse reactions to the vaccine.

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