A shot in the arm
Vaccines come in different forms
Vaccinations work by giving the immune system a controlled first exposure to a disease. Exposed to the antigens in the vaccine, your immune cells start making antibodies and also produce long-lived memory T cells and memory B cells. If your immune system encounters the same antigen again, the memory cells ensure that many specific antibodies are made quickly and in greater quantity, so you are much less likely to get ill from that disease.
Ideally, vaccines against a particular pathogen will be delivered into the body the same way as the pathogen itself, such as a vaccine against influenza that is inhaled.
What is in a vaccine? Some use only pieces of the DNA – certain antigens or DNA encoding antigenic memory B cells – that trigger an immune response but don’t cause disease on their own. Other vaccines contain dead (inactivated) pathogens. Some vaccines, such as the measles, mumps and rubella (MMR) vaccine, are made with live attenuated (weakened) versions of the pathogen. Live vaccines are usually the best at provoking an immune response but they have to be kept refrigerated. They also pose the very small risk that the live pathogen will mutate to an infectious form. For example, it’s estimated that the live virus in the oral polio vaccine can cause paralysis in about 1 in 2.5 million doses of the vaccine. Ideally, vaccines against a particular pathogen will be delivered into the body the same way as the pathogen itself, such as a vaccine against influenza that is inhaled.
So why don’t we have vaccines for all diseases? For some, scientists haven’t been able to provoke a strong enough immune response using the usual vaccine designs. For others, there may be several promising vaccines, but rigorous safety and efficacy testing means that it may take years before a vaccine becomes available. Or it may be that more funding is needed.
Vaccination can completely wipe out some diseases, as in the case of smallpox, which was declared eradicated in 1980. In other cases, to keep a disease from spreading, a high proportion of the population must be vaccinated. This is called ‘herd immunity’. The measles outbreak in Wales in 2013 was due to falling vaccination levels, which meant that infected people were more likely to come into contact with others who were unprotected.Lead image:
Illustration © Glen McBeth
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