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09 18 2021
Simple vaccine principle, why does the vaccine need two doses to have complete protection | Aquasky

Simple vaccine principle, why does the vaccine need two doses to have complete protection 

The Covid-19 vaccine that can be seen today requires two doses of vaccine except for the American Johnson & Johnson vaccine. According to the latest research in the United Kingdom, a single dose of Pfizer BNT or AstraZeneca AZ vaccine can reduce the incidence of severe illness to more than 80%. This study is based on the data of the first batch of vaccinated people over 80 years of age. Therefore, people are beginning to pay attention to whether to administer one dose of vaccine or to complete two doses of vaccinations.

 

In fact, experts suggest that two full doses of the vaccine should be given to obtaining complete protection. The reason is actually related to the principle of the vaccine itself. Most vaccines require follow-up boosters to achieve full effect. Take the measles, mumps, and rubella vaccine (MMR) as an example. According to a study of newborns vaccinated at birth, 40% of those who have received only one shot are not fully immune to these three viruses. Only4% of those had received 2 doses. Danny Altmann, professor of immunology at Imperial College London, explained that follow-up boosters can stimulate the vaccinators' autoimmune function into a new mode of fine-tuning.

 

When the body’s immune system first encounters a vaccine, it activates two important white blood cells. One is plasma B cells, which primarily focus on making antibodies. But their life is quite short. A large number of antibodies will be produced in the body within a week, and the antibody will drop sharply without a second dose of vaccine. The other is T cells, also known as T lymphocytes, which differentiate into different effector subtypes after maturation, which can recognize and kill different pathogens. One of them is called a memory T cell. If it does not encounter the target (virus), it can survive in the body for decades. This means that some vaccines can provide lifelong immunity. The key is that such T cells will only be produced in large quantities after "a second shot of the vaccine is given." By injecting the subsequent booster of the vaccine, the body is exposed to the antigen for the second time. That is the molecule on the pathogen that triggers the immune system, thereby activating the second stage of the immune response.

 

The second dose of vaccine is used as a booster. In addition to the increase in the number of T cells in the body, if the previously produced and active B cells encounter the pathogen again, they will divide rapidly to produce higher-quality antibodies. The second dose of vaccine will also promote the initiation of "B-cell maturation", which specifically includes selecting the batch of immature B-cells whose receptors are best bound to a specific pathogen. This screening process is carried out in the bone marrow that produces white blood cells. After this process is over, B cells, which are "essential", enter the spleen, where they complete their development. This also means that the vaccine as a booster will not only increase the number of B cells but also produce a more accurate antibody identification rate. Although the British officially announced that Pfizer and AZ had a significant effect after the first dose of the vaccine, the expert’s advice is that people who only received one dose of the vaccine should “pretend not to be vaccinated” and wear a mask before the injection. Wash your hands, maintain social distance, and it's the same after the injection. British public medical officials also emphasized the importance of the second dose of vaccine, because the second dose of vaccine "is very likely to strengthen the immune response, make it more mature, cover a wider range, and last longer." Deborah Dunn-Walters, professor of immunology at the University of Surrey, also pointed out that it takes time to develop immunity. Therefore, for any kind of vaccine, whether you vaccinate once or twice, your immunity will be the same as before the injection for a few weeks after the first injection.

 

The human body’s immune system can be simply divided into two parts. One is the innate immune system (also known as innate immunity), which consists of human organs such as the skin that resist infection, and the other part is white blood cells and chemical mechanisms. Vaccines have no impact on innate immunity. Moreover, this part of the system alone is not enough to prevent diseases. The other part is the acquired immune system (also called adaptive immunity), which produces the function of identifying and initiating an immune response against specific pathogens through contact with them. And this kind of adaptation and acquisition process requires time. In other words, the body must be stimulated by the vaccine to produce more immune cells, and some immune cells will further produce antibodies.

 

Nowadays, people are most concerned about the effectiveness of vaccines. The main evaluation is based on observing whether there are symptoms after another, rather than measuring whether it is infected. Asymptomatic infections are also occurring in various places. At present, there is not enough evidence to prove that the completion of single-dose or double-dose vaccine administration can prevent the spread of the virus. However, data from clinical studies show that a shot of the vaccine is indeed insufficient. It has been a while since countries around the world started to inject The Covid-19 vaccine, but it may still take some time to return to the level before the pandemic.

 

 

 

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