Smallpox primary prevention

{{Small pox]] Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

The smallpox vaccine helps the body develop immunity to smallpox. The vaccine is made from a virus called vaccinia which is a “pox”-type virus related to smallpox. The smallpox vaccine contains the “live” vaccinia virus—not dead virus like many other vaccines. For that reason, the vaccination site must be cared for carefully to prevent the virus from spreading. Also, the vaccine can have side effects. The vaccine does not contain the smallpox virus and cannot give you smallpox.

Currently, the United States has a big enough stockpile of smallpox vaccine to vaccinate everyone in the United States in the event of a smallpox emergency.

Vaccination history

At the age of thirteen, Jenner was apprenticed to Dr. Ludlow in Sodbury. He observed that people who caught cowpox while working with cows were known not to catch smallpox. He assumed a causal connection. The idea was not taken up by Dr. Ludlow at that time. After Jenner returned from medical school in London, a smallpox epidemic struck his home town of Berkeley, England. He advised the local cow workers to be inoculated. The farmers told him that cowpox prevented smallpox. This confirmed his childhood suspicion, and he studied cowpox further, presenting a paper on it to his local medical society.

Perhaps there was already an informal public understanding of some connection between disease resistance and working with cows. The “beautiful milkmaid” seems to have been a frequent image in the art and literature of this period. But we know for a fact: In the years following 1770 there were at least six people in England and Germany (Sevel, Jensen, Jesty 1774, Rendall, Plett 1791), who tested successfully the possibility of using the cowpox vaccine as an immunization for smallpox in humans. In 1796 Sarah Nelmes, a local milkmaid, contracted cowpox and went to Jenner for treatment. Jenner took the opportunity to test his theory. He inoculated James Phipps, the eight-year-old son of his gardener, not with smallpox but with cowpox. After an extremely weak bout of cowpox, James recovered. Jenner then tried to infect James with smallpox but nothing happened—the boy was immune to smallpox. Thanks to the development of the smallpox vaccine, the disease was officially eradicated in 1979.

Jenner reported his observations to the Royal Society. Further work was suggested, and Jenner published a series of 23 cases, including his son Edward, none suffered severely from smallpox. Two years later a society to oppose vaccination had been established in Boston, Massachusetts — an indication of rapid spread and deep interest. By 1800 Jenner’s work had been published in all of the major European languages. The process was performed all over Europe and the United States. The death rate was close to zero with the process, which became known as vaccination and was continued to around 1974 in the UK. A typical death rate at that time was roughly one per million, making vaccination against smallpox with vaccinia the most dangerous immunisation widely provided in modern times.

The Balmis Expedition (1803) carried the vaccine to Spanish America, the Philippines and China under commission of the Spanish Crown.

Some years before Dr. Jenner, Benjamin Jesty, a farmer at Yetminster in Dorset (he later moved to and is buried at Worth Matravers) is recorded as observing the two milkmaids living with his family to have been immune to smallpox and then inoculating his family with cowpox to protect them from smallpox. This was done in 1774 and can be found with Crookshank's History and Pathology of Vaccination, London 1889, vol. 1, p.110ff. But the question of who first initiated smallpox inoculation/vaccination can not be answered properly, as there is in the sources the exact date and time only for the predecessor Plett (1791), but not for Sevel, Jensen and Rendall. Louis T. Wright, an African-American and Harvard medical school graduate (1915), introduced intradermal vaccination for smallpox for the soldiers while serving in the Army during World War I.

Current vaccine

Length of protection

Smallpox vaccination provides high level immunity for 3 to 5 years and decreasing immunity thereafter. If a person is vaccinated again later, immunity lasts even longer. Historically, the vaccine has been effective in preventing smallpox infection in 95% of those vaccinated. In addition, the vaccine was proven to prevent or substantially lessen infection when given within a few days of exposure. It is important to note, however, that at the time when the smallpox vaccine was used to eradicate the disease, testing was not as advanced or precise as it is today, so there may still be things to learn about the vaccine and its effectiveness and length of protection.

Receiving the vaccine

The smallpox vaccine is not given with a hypodermic needle. It is not a shot as most people have experienced. The vaccine is given using a bifurcated (two-pronged) needle that is dipped into the vaccine solution. When removed, the needle retains a droplet of the vaccine. The needle is used to prick the skin a number of times in a few seconds. The pricking is not deep, but it will cause a sore spot and one or two droplets of blood to form. The vaccine usually is given in the upper arm.

If the vaccination is successful, a red and itchy bump develops at the vaccine site in three or four days. In the first week, the bump becomes a large blister, fills with pus, and begins to drain. During the second week, the blister begins to dry up and a scab forms. The scab falls off in the third week, leaving a small scar. People who are being vaccinated for the first time have a stronger reaction than those who are being revaccinated. The following pictures show the progression of the site where the vaccine is given.

Post-vaccination

After vaccination, it is important to follow care instructions for the site of the vaccine. Because the virus is live, it can spread to other parts of the body, or to other people. The vaccinia virus (the live virus in the smallpox vaccine) may cause rash, fever, and head and body aches. In certain groups of people, complications from the vaccinia virus can be severe.

Vaccine benefit

Vaccination within 3 days of exposure will prevent or significantly lessen the severity of smallpox symptoms in the vast majority of people. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may modify the severity of disease.

Safety

The smallpox vaccine is the best protection you can get if you are exposed to the smallpox virus. Anyone directly exposed to smallpox, regardless of health status, would be offered the smallpox vaccine because the risks associated with smallpox disease are far greater than those posed by the vaccine.

There are side effects and risks associated with the smallpox vaccine. Most people experience normal, usually mild reactions that include a sore arm, fever, and body aches. However, other people experience reactions ranging from serious to life-threatening. People most likely to have serious side effects are: people who have had, even once, skin conditions (especially eczema or atopic dermatitis) and people with weakened immune systems, such as those who have received a transplant, are HIV positive, are receiving treatment for cancer, or are currently taking medications (like steroids) that suppress the immune system. In addition, pregnant women should not get the vaccine because of the risk it poses to the fetus. Women who are breastfeeding should not get the vaccine. Children younger than 12 months of age should not get the vaccine. Also, the Advisory Committee on Immunization Practices (ACIP) advises against non-emergency use of smallpox vaccine in children younger than 18 years of age. In addition, those allergic to the vaccine or any of its components should not receive the vaccine. Also, people who have been diagnosed by a doctor as having a heart condition with or without symptoms, including conditions such as previous myocardial infarction (heart attack), angina (chest pain caused by lack of blood flow to the heart), congestive heart failure, and cardiomyopathy (heart muscle becomes inflamed and doesn’t work as well as it should), stroke or transient ischemic attack (a “mini-stroke” that produces stroke-like symptoms but not lasting damage), chest pain or shortness of breath with activity (such as walking up stairs), or other heart conditions being treated by a doctor should not get the vaccine at this time. (Heart disease may be a temporary exclusion and may change as more information is gathered.) Also, individuals who have 3 or more of the following risk factors should not get the vaccine at this time: high blood pressure diagnosed by a doctor; high blood cholesterol diagnosed by a doctor; diabetes or high blood sugar diagnosed by a doctor; a first degree relative (for example, mother, father, brother or sister) with a heart condition before the age of 50; and/or, currently a cigarette smoker. (These may be temporary exclusions and may change as more information is gathered.)

In the past, about 1,000 people for every 1 million people vaccinated for the first time experienced reactions that, while not life-threatening, were serious. These reactions included a toxic or allergic reaction at the site of the vaccination (erythema multiforme), spread of the vaccinia virus to other parts of the body and to other individuals (inadvertent inoculation), and spread of the vaccinia virus to other parts of the body through the blood (generalized vaccinia). These types of reactions may require medical attention. In the past, between 14 and 52 people out of every 1 million people vaccinated for the first time experienced potentially life-threatening reactions to the vaccine. Based on past experience, it is estimated that 1 or 2 people in 1 million who receive the vaccine may die as a result. Careful screening of potential vaccine recipients is essential to ensure that those at increased risk do not receive the vaccine.

Availability

Routine smallpox vaccination among the American public stopped in 1972 after the disease was eradicated in the United States. Until recently, the U.S. government provided the vaccine only to a few hundred scientists and medical professionals working with smallpox and similar viruses in a research setting.

After the events of September and October, 2001, however, the U.S. government took further actions to improve its level of preparedness against terrorism. One of many such measures—designed specifically to prepare for an intentional release of the smallpox virus—included updating and releasing a smallpox response plan. In addition, the U.S. government has enough vaccine to vaccinate every person in the United States in the event of a smallpox emergency.