Smallpox Vaccine and Cancer

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Some background on the smallpox vaccine

The vaccine’s history

Smallpox is a highly contagious and sometimes fatal infectious disease. There is no treatment for smallpox, and the only way to prevent it is vaccination.

As many older adults may recall, smallpox vaccine was once given as a part of routine childhood immunizations. At that time, few cancer patients were vaccinated, and AIDS (acquired immunodeficiency syndrome) was unheard of. Smallpox vaccination in the United States was stopped in 1972 because there had been no reports of smallpox since 1949. Widespread immunization had caused the virus to be wiped out in the United States.

In the rest of the world, smallpox was done away with by 1977 through careful tracking of every case and vaccination of all possible contacts (people who had been exposed to the person with smallpox). At that time, experts believed that the only smallpox virus left in the world were lab samples in the former Soviet Union and the United States, and these were tightly guarded. But since September 2001, it’s been thought that other countries or groups might have kept or gotten smallpox virus, and could use it as a weapon.

The vaccine today

The smallpox vaccine used today is called ACAM2000. It’s not available to the general public, although a smallpox outbreak would change that. As of early 2014, the only people who might get the vaccine are:

  • Certain members of the US military
  • Those selected by state public health preparedness programs
  • People who work in labs that handle smallpox virus

In response to bioterrorism concerns, plans have been made to respond to a smallpox emergency. Enough smallpox vaccine has been stockpiled to vaccinate every person in the United States. If a smallpox outbreak occurs, public health officials will say who should get vaccinated at that time. If there is a smallpox outbreak, vaccinations may need to be repeated every 3 to 10 years.

Concerns about the vaccine

The vaccine against smallpox uses a live virus called vaccinia. It’s not the smallpox virus, and you cannot get smallpox from the vaccine. The vaccinia virus rarely causes illness. The vaccine makes a person immune to the smallpox virus.

When children got the smallpox vaccine as part of their routine childhood immunizations, only a few became ill from it. Most of the children who did get sick already had skin problems such as burns, impetigo, or eczema. The vaccinia virus would infect these breaks in the skin, which led to serious infections in some children that in rare cases caused death.

Another group of children who had inherited diseases that caused weak immune systems also had trouble with the vaccine. These children were not able to produce an immune defense to the usually-mild vaccinia infection, and some became seriously ill and died.

Serious and sometimes fatal illnesses have also happened when children with undiagnosed leukemia or lymphoma were vaccinated.

Special concerns for people with weak immune systems

Because of the vaccine problems that have happened in the past, doctors are concerned about the way the smallpox vaccine could affect people with weakened immune systems if emergency vaccination were ever needed.

People with poor immune function are said to be immunosuppressed. This includes people with certain illnesses:

  • Those with certain chronic diseases like liver disease, lupus, or other problems that affect the immune system
  • Those who have had organ transplants, including stem cell or bone marrow transplants
  • Those who take medicines that suppress the immune response (this is often called immunosuppressive therapy)
  • Those with HIV infection or AIDS
  • Most people with cancer – especially those being treated and those who have had bone marrow or peripheral blood cell transplants

Harm from the vaccine: People whose immune systems are not working well are most likely to have serious problems if they get the vaccine.

Getting the infection from someone who has gotten the vaccine: Even if they do not get the vaccine themselves, people with poor immune function can get vaccinia infection from vaccinated friends or family members.

A vaccinated person can shed virus from the vaccine site for up to 21 days after the vaccination. Vaccinia can be spread by touching a vaccination site before it has fully healed. It can also be spread by touching bandages, towels, washcloths, or clothes that have picked up live virus from the vaccination site. Vaccinia is NOT spread through the air.

There have been many reports of people who got a vaccinia infection from vaccinated people. Most of the time, these people already had skin problems such as eczema, sores, or broken skin. Touching something that had vaccinia virus on it allowed the virus to invade areas where the skin was open. Sometimes people became infected because of prolonged close contact with a person who was recently vaccinated. Any person whose immune system is not working well should be careful to avoid contact with people vaccinated within the last 21 days. (See the information under “What is ‘close contact?’” in the section “Smallpox vaccine safety for people with cancer.”)

Like other newly vaccinated people, health care workers can also transmit the vaccinia virus within 21 days of vaccination. But this should not be a problem, because these workers can cover their vaccination sites while at work. In some cases, they may be given time away from caring for certain patients; for instance, those with skin problems or immune deficiencies.

Larger problems may happen if the general public is vaccinated at some point in the future. People with poor immune function may find it hard to avoid being exposed to those who were recently vaccinated.


Last Medical Review: 02/24/2014
Last Revised: 02/24/2014