Does this mean that a vaccine will also fail to protect against the virus? Certainly not. First, it is still unclear how common this rescheduling is. More importantly, fading immunity to natural infections,
Any infection initially activates a non-specific immune response, in which white blood cells stimulate inflammation. This may be enough to clear the virus. But in more prolonged infections, the adaptive immune system is activated. Here, T and B cells recognize the specific structure (or antigens) derived from the virus. T cells can detect and kill infected cells, while B cells produce antibodies that neutralize the virus.
During the primary infection – that is, the first time a person has been infected with a particular virus – this adaptive immune response is delayed. To control the infection it takes a few days before the immune cells that activate the pathogen become active and proliferate.
Some of these T and B cells, called memory cells, last long after the infection has resolved. It is these memory cells that are crucial for long-term protection. In subsequent infections by the same virus, memory cells become active quickly and induce a strong and specific response to block the infection.
A vaccine mimics this primary infection, provides antigens that induce adaptive immunity, and produces memory cells that can be quickly activated in the event of an actual infection. However, as the antigens in the vaccine are taken from weak or non-infected material from the virus, there is less risk of serious infection.
Better immune response
Vaccines have other benefits from natural infections. For one, they can be designed to concentrate the immune system against certain antigens that give better responses.
The natural immunity against HPV is particularly weak, as the virus uses a variety of tricks to bypass the host’s immune system. Many viruses, including HPV, contain proteins that inhibit the immune system or come down only to avoid detection. Indeed, a vaccine that provides accessible antigens in the absence of these other proteins may allow us to control the response in a way that does not give a natural infection.
The immunogenicity of a vaccine – that is, how effective it is in producing an immune response – can also be beautiful. So-called adjuvant agents usually initiate an immune response and the vaccine can boost the immune system.
With this, the dose and route of administration can be controlled, in order to promote the right immune response in the right place. Traditionally, measles-like respiratory viruses are also vaccinated by intramuscular injection. In this case, the vaccine produces such a strong response that antibodies and immune cells reach the mucosal surface in the nose.
Understanding natural immunity is key
Maitreyi Shivkumar D is a Senior Lecturer in Molecular Biology at Montfort University.
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