The second dose of the vaccine uses natural mechanisms in the body to produce a more effective response, but if the second dose is another vaccine, can it also work?
Johnson & Johnson’s SARS-CoV-2 vaccine only needs to be injected once to immunize people. So why do other vaccines such as AstraZeneca or Pfizer BioNTech need two doses?
Some governments and certain groups of people have ordered the suspension of AstraZeneca’s vaccination, which also raises a question: What will happen if only one dose of the vaccine is given?
Types of coronavirus vaccines
Amazing B cells
Usually, the second dose of vaccine activates a key part of our immune system: B cells.
If people who have not yet been infected with the coronavirus receive the first dose of the vaccine, their cells will begin to produce spike protein, which can be used to infect other cells. B lymphocytes are specialized cells of the immune system, which bind to the protein through specific receptors. When the receptor matches the spike protein, the B cell is activated.
Then, the activated B cells reach the nearest lymph nodes, where they multiply rapidly with the support of other cells of the immune system (helper T cells).
The human body contains about 10 billion different B cells, which have slightly different receptors from each other and can bind to every imaginable protein structure. No matter what the infection is, our body is ready to deal with it.
In fact, B cells have been genetically programmed to display this diversity, so as to generate random combinations of genes when they multiply, and have more than 1,000 billion different combinations.
What is the second dose of the vaccine?
When B cells recognize the antigens of their receptors, they begin to make antibodies and release them into the blood. Antibodies are molecules that match the proteins, antigens (in this case, the coronavirus spike) that they have identified, and can block them. Therefore, they eliminate intruders and allow them to leave without entering a “key”.
But this process is not perfect, and the antibody cannot match the antigen exactly. This is why the human body has evolved a self-improving system: the offspring of the first B lymphocytes will evolve over time. Their variation is very small, some have better effects on antigens, while others are worse. Therefore, within a few weeks, the body has a fine-tuned response to the aggressor.
Cells with better effects will receive stronger signals, proliferate and become memory cells, that is, specialized B cells, which can store the correct protein combination to immunize us in the future.
It is this mechanism that is the reason for the second vaccination and the reason why the vaccination is only two to three weeks after the second vaccination. On the one hand, give the body some time for the B cells to improve their response.
When the second dose arrives, you are mimicking the second infection. Memory cells with well-functioning receptors are found in the blood, recognize the spike protein, and then turn on the antibody-producing mechanism again. In the second round, the antibody was more effective than the first round.
Side effects of the second dose of vaccine
The effectiveness of booster vaccines also depends on the type of vaccine. MRNA vaccines are wrapped in fat, and the immune system has no chance to recognize them. You must wait for the messenger RNA’s instructions to start producing spike proteins, and then make the immune system react. After the second vaccination, a large amount of antigen will be produced, which will lead to an enhanced response.
Therefore, in the case of Moderna and Biontech/Pfizer, the side effects of the second dose are greater. However, the use of AstraZeneca vector vaccines is another matter: the first response is the one that produces the most symptoms, because it is equivalent to simultaneously infecting 50 billion inactivated viruses, which is impossible to achieve. Natural infection. The response from the second dose was milder.
Therefore, the Johnson & Johnson vaccine that also uses a carrier does not require booster immunization, because a single dose response is sufficient to produce a large number of antibodies. Johnson & Johnson found that its vaccine has an effective rate of 66%, while AstraZeneca’s two-dose vaccine has an average effective rate of 70%.
however, A study published in The Lancet Shows that a single dose of AstraZeneca has reached 70%. This may make people who receive only one dose have sufficient immunity.
There are also good arguments for combining one vaccine with another. It is unusual for the same carrier to be used for the initial and booster immunizations of AstraZeneca vaccine. The Russian Sputnik V vaccine uses two different adenoviruses.
This may be the reason for the trial because AstraZeneca vaccines and other brands of vaccines are supplemented in the booster immunization schedule of other brands (such as the Biontech-Pfizer brand).