Non-specific effect of vaccines

Non-specific effects of vaccines refer to the unintended consequences, either beneficial or harmful, that vaccines may have on the immune system. These effects are not related to the specific protective effects against the targeted diseases.

Overview

The concept of non-specific effects of vaccines was first proposed in the 1980s. It was observed that some vaccines have effects on the overall mortality and morbidity that cannot be explained by the prevention of the target diseases. These effects were seen in both high and low-income countries and were particularly pronounced in low-income countries where infectious diseases are a major cause of death.

Types of Non-Specific Effects

Non-specific effects can be either beneficial or harmful. Beneficial non-specific effects include enhanced immune responses to non-target pathogens and reduced susceptibility to unrelated infections. Harmful non-specific effects include increased susceptibility to non-target infections and enhanced disease severity.

Beneficial Non-Specific Effects

Some vaccines, such as the BCG vaccine for tuberculosis and the measles vaccine, have been shown to have beneficial non-specific effects. These vaccines have been associated with a reduction in overall mortality that is greater than can be explained by the prevention of their target diseases. The mechanisms behind these beneficial effects are not fully understood, but they may involve "training" of the innate immune system to respond more effectively to infections.

Harmful Non-Specific Effects

Other vaccines, such as the DTP vaccine for diphtheria, tetanus, and pertussis, have been associated with harmful non-specific effects. Some studies have suggested that these vaccines may increase susceptibility to non-target infections or enhance the severity of these infections. The mechanisms behind these harmful effects are not fully understood.

Mechanisms

The mechanisms behind the non-specific effects of vaccines are not fully understood. Some researchers believe that these effects may be due to "trained" immunity, a concept that suggests that the innate immune system can develop a form of memory that enhances its response to subsequent infections. Other researchers believe that these effects may be due to changes in the composition of the microbiome, the community of microorganisms that live in and on the body.

Research

Research into the non-specific effects of vaccines is ongoing. This research is important because it may lead to the development of new vaccines that have beneficial non-specific effects and avoid harmful ones. It may also lead to changes in vaccination schedules to maximize the beneficial non-specific effects and minimize the harmful ones.

See Also

• Vaccine
• Immunology
• Infectious disease