As many adults are aware, smallpox vaccine was once given as a part of routine childhood immunizations. At the time, few cancer patients were vaccinated, and acquired immunodeficiency syndrome (AIDS) was unheard of. Smallpox vaccination in the United States was stopped in 1972 because there had been no smallpox infections since 1949. Because of the widespread immunization, the virus was wiped out in the United States.

By 1977, smallpox was done away with in the rest of the world through stringent tracking of every case and vaccination of all possible contacts (people who had been exposed to the person with smallpox.) At this point, experts believed that the only remaining samples of smallpox virus were in the former Soviet Union and the United States, and that they were tightly guarded.

But now it is believed that other countries or groups might have kept or obtained this virus, and that they could use it as a weapon. Because of this, the government has moved to vaccinate certain health care workers and military personnel. Although there is enough vaccine in the United States for everyone if needed, the vaccine is not available to the general public at this time. Still, doctors have raised concerns about the way vaccines could affect people with weakened immune systems if widespread vaccination occurs. This would include many cancer patients, especially those being treated with chemotherapy, radiation, and stem cell transplants.

The Vaccine

The vaccine against smallpox uses a live virus called vaccinia. It is not the smallpox virus, and you cannot get smallpox from the vaccine. The vaccinia virus is similar to the smallpox virus, but rarely causes any illness. It does, however, protect the person by making them immune to the smallpox virus.

In the past, children got the smallpox vaccine as part of their routine childhood immunizations. Only a few became ill from it. Most of the children who fell ill already had widespread skin diseases such as 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 unable 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 occurred in the past when children with undiagnosed leukemia or lymphoma were vaccinated.

Problems for People With Decreased Immune Function

People whose immune systems are not working well, which includes those with certain chronic diseases, transplanted organs (due to the medicines they must take), as well as those with HIV, are most likely to be harmed by the vaccination. This includes most cancer patients -- especially those being treated and those who have had bone marrow or peripheral blood cell transplants. People in these situations are said to be immunosuppressed.

These people can also be infected with the vaccinia virus from a recently vaccinated person. A vaccinated person can shed virus from his or her skin for up to 21 days after the vaccination. Vaccinia can be spread by touching a vaccination site before it has healed. It can also be spread by touching bandages or clothes that have been contaminated with 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 major skin problems such as eczema or other problems that caused a lot of sores or broken skin. Touching something that had vaccinia virus on it allowed the virus to invade these areas where the skin was open. Sometimes they became infected because of prolonged close contact. Any person whose immune system is not working well should be careful to avoid contact with people vaccinated within the last 21 days (see information below about contact).

Health care workers can also transmit the virus within 21 days of vaccination. But this should be a minor problem since these workers can cover their vaccination sites. In a few cases, they may be given time away from caring for patients, especially those with skin problems or immune deficiencies.

Larger problems may occur if the general public is vaccinated at some point in the future. Patients with poor immune function may have a harder time avoiding being exposed to vaccinated friends or family members.

Questions and Answers

Which cancer patients should avoid the vaccine?

Any patient whose immune system is not working well should not get a routine smallpox vaccination because of the increased risk of serious side effects. This means that any person being treated or having recently been treated for cancer -- especially with chemotherapy or radiation -- should not receive the vaccine (unless a smallpox outbreak occurs and they have already been exposed to smallpox). Patients who have no immune system problems may be considered for the vaccine. Each patient should discuss his or her specific situation with his or her doctor.

What kinds of precautions should the cancer patient take?

They should avoid close contact with people who have been recently vaccinated unless the vaccination site is covered with a gauze bandage and a special dressing (semi-permeable dressing) recommended by the Centers for Disease Control and Prevention (CDC). As of 2007, the people most likely to get the smallpox vaccine include military recruits and certain laboratory workers.

If an infection should occur in a person with cancer despite all precautions, symptoms might include rash, fever, and head and body aches. The patient should see a doctor who specializes in infections (an infectious disease specialist) as soon as possible.

What is "close contact?"

The CDC defines close contact as household or similar intimate physical contact. This means that anyone who has had a smallpox vaccination should not be in the home of a person who has active cancer for at least 21 days after the vaccination. A person with cancer should not be in the home of anyone who has had a smallpox vaccination within 21 days of their vaccination. Because the virus is passed through direct contact, it is not likely that a person will become infected at the workplace, gym, or public transportation.

The main concern for people who have close, physical contact with someone who has been vaccinated is that the vaccinia virus can be spread from the vaccination site. Vaccinia is spread by touching a vaccination site before it has healed or by touching bandages, clothing, or other material contaminated with live virus from the vaccination site and then touching another part of the body or touching someone else. The vaccination site often becomes itchy, which may lead to scratching, rubbing, or touching the site. That increases the risk that the virus will end up on other parts of the body, or on clothing and other material.

Are there other people who should not take the vaccine?

• People who are allergic to any part of the vaccine, including certain antibiotics and latex, cannot take it. 
• People with skin conditions that cause sores or breaks in the skin should not take the vaccine. 
• Women who are pregnant or breastfeeding should not take the vaccine. 
• Anyone who is taking medicines that suppress the immune system should not take the vaccine. 
• People who have short-term skin problems such as burns, poison ivy, or other conditions causing broken skin should not take the vaccine until their skin has healed. 
• People with certain heart conditions should not take the vaccine for routine prevention.

In the event that any of these people are actually exposed to smallpox, the situation may change for some of them. In such a case, the risk of smallpox may be higher than the risk of taking the vaccine. This situation should be discussed with a doctor.

For more information, you can find the CDC's smallpox vaccine information on their Web site at: http://www.bt.cdc.gov/agent/smallpox/vaccination/vaccine.asp, or call them at 1-800-CDC-INFO (TTY 888-232-6348).

References

Breman JG, Arita I, Fenner F. Preventing the return of smallpox. N Engl J Med. 2003;348:463-466.

Blendon RJ, DesRoches CM, et al. The public and the smallpox threat. N Engl J Med. 2003;348:426-432.

Centers for Disease Control and Prevention (CDC). Household transmission of vaccinia virus from contact with a military smallpox vaccinee--Illinois and Indiana, 2007. Morb Mortal Wkly Rep. 2007;56:478-481.

Centers for Disease Control and Prevention. Smallpox: Information for Specific Groups. 2005. Available at: http://www.bt.cdc.gov/agent/smallpox/index.asp. Accessed November 20, 2007.

Centers for Disease Control and Prevention. Smallpox Vaccine Information Statement. Available at: http://www.bt.cdc.gov/agent/smallpox/vaccination/pdf/smallpox-vis.pdf. Accessed November 20, 2007.

Centers for Disease Control and Prevention (CDC). Vulvar vaccinia infection after sexual contact with a military smallpox vaccinee--Alaska, 2006. Morb Mortal Wkly Rep. 2007;56:417-419.

Revised: 12/03/2007