Booster dose (vaccine)

A booster dose (vaccine) is an additional dose of a vaccine that is given after the initial immunization. It helps strengthen the body’s immune response to the original vaccine and provides additional, longer lasting protection from disease. Booster shots, as they are sometimes called, work by re-exposing the body to the ingredients in the original vaccine that protect against illness. Not all vaccines require booster doses, and some require more than one booster. Scientists are largely unsure why some vaccines provide lifetime immunity and others require booster doses.

Background

Vaccines are substances administered to help the body develop immunity to a specific disease. Some are administered through the nose or mouth, but most are given through an injection. They work by introducing the body to a form of a bacteria or virus. This causes an immune response, or the production of antibodies that help fight the bacteria or virus. Once antibodies are present, it is easier for the immune system to stop the bacteria or virus from causing illness.

Vaccines have a long history of use and were developed and used even before humans gained a full scientific understanding of disease transmission and immunity. The first vaccine was for smallpox and developed in the late 1700s. By the mid-twentieth century, researchers had developed vaccines for seven more diseases, including polio, that killed thousands every year. Because of vaccines, smallpox all but disappeared, and people in developed countries were no longer needed to be vaccinated against it by the early 1970s.

By the early twenty-first century, vaccines were available to prevent or reduce the severity of a variety of human diseases. Diseases and boosters to protect animals from some diseases were also available. Booster doses gained renewed attention in the early 2020s following the release of vaccines to combat the COVID-19 pandemic, which had spread around the world in early 2020. Many of the most popular and effective vaccines released in the United States, including the vaccine manufactured by Pfizer, required booster doses in order to maintain their efficacy; as a result, medical professionals and public health experts faced the challenge of communicating the importance of booster doses. Some of these booster shots were specifically designed to provide immunity against new variants of COVID-19, including the Omicron variant.

Overview

Vaccines work by introducing the body to an antigen, or a substance that can trigger a response from the body’s immune system. Antigens can be any bacteria, viruses, chemicals, pollen, dust, and more. The antigen prompts the immune system so that the organs, the white blood cells, and other parts of this system respond with antibodies. An antibody is a protein made by the body that recognizes that specific antigen and works to protect the body from its effects. When there are not enough antibodies or they are not effective enough, illness results.

Vaccines introduce the body to a controlled amount of an antigen so that the body learns to produce antibodies against it. In the case of diseases, the antigen is usually a small amount of the bacteria or virus that may already be dead. It can also be a form of the bacteria or virus that is manufactured in a laboratory. The antigen is introduced in an amount and form that is not strong enough to cause the disease; it is just enough to prompt the immune system to respond. Once this response is triggered, the body will recognize the antigen and be able to respond with the appropriate antibodies if it is exposed to the same antigen again. As a result, illness from that antigen will either be avoided or lessened in severity.

For reasons experts do not fully understand, some vaccines produce a long-lasting or permanent response to the antigen. This is called having immunity to the antigen and the diseases it causes. In some cases, however, a single exposure to the antigen is not enough to develop lasting immunity. The antigen may not produce enough antibodies to prompt full immunity, or the antibodies may fade in number or strength over time. Experts believe that the speed with which the initial immune response occurs may play a role in how long immunity lasts. They think that a fast response may not allow the immune system enough time to develop sufficient memory for a long-lasting response. In these cases, booster doses are administered.

A booster dose is usually a smaller dose of the same antigen administered in the first or primer vaccination. Boosters are generally as safe as the original vaccine. They can also cause similar adverse reactions to those caused by the vaccine. These can include localized swelling, redness, pain, and muscle aches, depending on the vaccine.

To determine when and how much of a booster is needed, scientists measure the number of antibodies that are present. They also measure the response of these antibodies to the reintroduction of the antigen. If the antibodies respond quickly and strongly, it is likely that the immune system can fight off the infection. A slower, less robust response means that another dose of the antigen might be needed to “boost” the immune system response.

The frequency with which booster doses are needed varies based on the original vaccine and other factors. In many cases, boosters are administered based on a general base of knowledge of how long the antibody response remains strong enough to prevent illness in most people. For example, boosters for the tetanus vaccine are recommended every ten years because the antigen response needs to be strengthened then. In other cases, tests are conducted to determine how well the antibodies will respond. When the immune response is already strong enough, administering a booster dose can cause an Arthus reaction, a localized response to the antigen that causes inflammation of the affected tissue. The reaction can cause severe pain, bleeding, and in some cases, necrosis or tissue death.

Booster doses may also be administered to people who are at increased risk of infection by a particular antigen. For example, people who are already immunocompromised, or who have an immune system that does not well, may not develop or keep immunity as long as others. Immunity can also fade with age, so boosters may be recommended as people get older. People who go to another country get immunized against diseases that occur there, such as typhoid or yellow fever. People in some occupations, such as healthcare workers and military personnel, may also get different vaccines and boosters based on diseases they might be exposed to that are not common to the general population.

Bibliography

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