What is a Virus? What are Viruses made up of ?
Vaccines have been developed to prevent several different viral diseases. They work by exposing the body to sufficient amount of virus to trigger an immune (antibody) response but not cause disease. This means that when a vaccinated person becomes infected with the virus for real, they can mount a faster, stronger immune response. Different types of vaccine have been developed; some use viruses that have been "attenuated", which means that they have been artificially evolved in the laboratory to be less able to cause disease. Others use inactivated virus or purified virus components that are incapable of replication in the body. These are safer, but less efficient at priming the immune response. It takes a long time to develop a safe and effective vaccine, because they need to be tested – first in the laboratory, then in animals and then in human clinical trials. Because vaccines tend to be very specific for the virus they are targeting, if a new variant of that virus appears, it may not be recognised by the antibodies produced against the virus used in the vaccine. For some very important viruses, the emergence of new variants is commonplace. For example, vaccines against influenza virus need constant re-configuration to best match the variants in circulation at the time, and this is why need a ‘flu shot every year.
An effective vaccine must be administered to a high enough percentage of the population to successfully protect a population. This is called herd immunity.
Antibiotics target specific aspects of bacterial replication, so are completely useless at treating viral infections. Antivirals prevent viral replication by targeting the host-cell machinery, meaning that they are often quite toxic.