[Epoch Times September 18, 2021](Epoch Times reporter Li Shaowei compiled a report) The goal of the vaccine is to stimulate the body to produce antibodies as if it is naturally infected with a certain virus or bacteria, so as to reduce severe illness or mortality. The protection of many vaccines can be maintained for a long time. Why is the protection period of the Covid-19 vaccine not long?
The measles vaccine can be used once and for all, one shot is enough; the protective power of the varicella vaccine can last for 10-20 years; the protective power of the tetanus vaccine can last about ten years. But now, adults who have been given the Covid-19 vaccine for six months will have to get another dose. why is that? Several experts interviewed by the Wall Street Journal (wsj) talked about their views.
Rustom Antia, a professor of biology at Emory University who studies immune responses, said: “If you get a vaccine, you won’t be infected even if you come into contact with this virus. This is the ideal vaccine. The effect. Unfortunately, not all vaccines can achieve this effect.”
Antiya said that protection has three meanings: preventing infection and virus transmission; preventing severe illness and virus transmission after infection; and only preventing severe illness. Protection includes many aspects, such as the strength of the body’s immune response triggered by the vaccine, the speed at which the antibodies produced fade away, whether the virus or bacteria will mutate, and the site of infection.
The cut-off value for protection is the minimum concentration of antibodies needed to prevent the body from developing symptoms of morbidity. This is different for different viruses and bacteria, and even how to determine the protection threshold. For example, some use the average antibody concentration in the blood, some need to consider different parts of the body, and others not only measure the level of antibodies, but also measure the level of neutralizing antibodies.
Mark Slifka, a professor at Oregon Health & Science University in the United States, said: “Basically, this (protective power threshold) is the level of antibodies or neutralizing antibodies per milliliter of blood.” , T cells will also provide protection, but it is still difficult to quantify and compare, and antibodies are easier to measure.
In 1942, two German researchers completed vaccine tests on animals and used their own physical tests to determine that the critical value for protection from tetanus was 0.01 International Units (IU) per milliliter of blood.
Slivka said: “One of them injected two doses of tetanus virus into his thigh to test his body’s response. Another researcher injected three doses of the virus.” As a result, none of them were affected by this. Virus infection, thereby determining the critical value of tetanus antibody protection.
The critical value of antibody protection required for measles was confirmed in 1985. A college student dormitory was exposed to measles virus due to blood donation activities. The researchers checked the antibodies in all students in the dormitory and found that 0.02 International Units (IU) of antibodies per milliliter of blood can prevent infection.
For these two infectious diseases, the combination of the strength of the antibody produced by the vaccine and the speed of the antibody decay, resulting in a longer-lasting protection of the vaccine. Antibodies to measles fade slowly; antibodies to tetanus fade faster, but the vaccine allows the body to produce a larger amount of antibodies, which offsets the factor of faster antibody regression.
Slivka said: “For these infectious diseases, we are fortunate to find their protective threshold. By tracking the decline in the level of antibodies in the body, we can calculate the effective time of the vaccine. But for the Covid virus, we don’t know.”
From the historical record, the most effective is the replication-type virus vector vaccine, this kind of vaccine basically has life-long protection. Both measles and chickenpox vaccines are in this category.
Non-replicating viral vector vaccines and protein-based vaccines (such as tetanus vaccine) are not as long as protective, but it is generally possible to increase the effectiveness of the vaccine by adding an adjuvant. Both tetanus and hepatitis A vaccines use an adjuvant.
The current vaccines of The Johnson & Johnson and AstraZeneca are non-replicating vector vaccines and do not contain adjuvants. Both Pfizer and Moderna are messenger RNA vaccines and do not contain any viruses.
The mutation of viruses and bacteria makes it possible for them to escape the body’s immune defenses, which makes the situation more difficult to control.
Measles, mumps, rubella and varicella virus will not mutate, but according to the British Medical Journal (British Medical Journal) statistics, the Covid-19 virus has so far had at least eight variants.
Slivka said: “This makes the vaccine more difficult. It must target different targets over time. Influenza viruses will also mutate. The practice of influenza vaccines is to develop new influenza vaccines that may be closest to new strains every year. “The protective power of the flu vaccine can last at least six months.
Since it is more complicated to develop a vaccine that can keep up with virus variants at any time, some people hope to achieve herd immunity against this virus. Antiya believes that this is also very difficult in the way that this type of coronavirus infects the human body.
“For most respiratory infectious diseases, vaccines are unlikely to achieve long-term herd immunity. Even if herd immunity is achieved, it will not last long. This depends on the speed of virus mutation and the rate of immunity fading.”
Part of the reason is that the coronavirus replicates in both the upper and lower respiratory tracts.
“Our lungs and body have better blood circulation (more antibodies), but the nasal cavity is worse (less antibodies). Our lower respiratory tract is better at preventing serious infectious diseases because there are a lot of antibodies.” Antiya said.
Therefore, the risk of mild infection of the upper respiratory tract will continue.
Researchers at Imperial College London said that the next Covid-19 vaccine is likely to be updated to fight the virus variants, and may focus on strengthening the immunity of the nose and lung mucosa.
These experts agreed that before a new vaccine is developed, the virus is now only a third shot. ◇
Editor in charge: Zhu Hanru
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