U.S. drug regulatory authorities approved the use of the Johnson & Johnson/Janssen vaccine in February 2021, but in April the vaccine was called off in multiple countries due to an increase in blood clot cases in the vaccine recipient population
The mass vaccination of the new crown vaccine is being rolled out worldwide, and research and development efforts continue, from the initial Pfizer and Modena vaccines being unrivaled in the world, to at least eight vaccines, to an increase in the number of vaccines approved for use.
What are the side effects of vaccination? Is it feasible to mix different vaccines?
There are also several basic questions you may need to know, including How much protection does the vaccine provide? How long does immune efficacy last? How do different vaccines compare, and more.
Nurse preparing for vaccination
What are the side effects of vaccines?
Vaccinations usually have some common side effects, where the body has an adverse reaction to the vaccine, but this is an indication that the vaccine is working and has successfully activated the body’s autoimmune response. There are also rare side effects, i.e. reactions to the vaccine that have a very low probability of occurring, and can be mild or severe.
The chemicals that are triggered by the vaccine and released naturally are called cytokines and chemokines, also known as chemotactic hormones and chemokines, which are protein signals secreted by cells.
The chemicals that activate the immune response cause discomfort, but are not usually severe enough to interfere with daily life, and the symptoms disappear after about three days.
Side effects can certainly occur after vaccination, but the key is the degree – the immune response must be neither too large nor too small, but just right; finding the best balance between side effects and immunity.
The most common known side effects of several major vaccines include localized pain at the site of the needle, fatigue, headache, and muscle pain. Other less common side effects include nausea, fever, and chills. As vaccination becomes more common, cases of rare side effects are beginning to increase.
The most notable of the rare cases were blood clot symptoms, involving both the Oxford/AstraZeneca vaccine and the Johnson & Johnson/Janssen vaccine. The AstraZeneca vaccine was once called off in a dozen countries in Beating Asia, and Johnson/Janssen was called off in the US, Europe and South Africa.
However, the jury is still out on whether there is a causal relationship between the New Crown vaccine and blood clots, and if so what the triggering mechanism is.
James Gallagher, BBC Health Science correspondent, answers questions.
Why do some people have more side effects?
Side effects vary greatly from person to person. Some people feel almost nothing; others feel slightly uncomfortable but are fine and can go to work; others are bedridden. Eleanor Riley, professor of immunology and infectious diseases at the University of Edinburgh, says, “There is a huge genetic diversity in our immune systems, and that’s the basis of the differences.” That diversity means that some people’s immune systems operate a little more hyper and are more likely to respond aggressively.
Do greater vaccine side effects mean greater protection?
Andrew Pollard, the professor in charge of the Oxford-AstraZeneca vaccine trial, says, “There have been precedents before – such as the 2009 pandemic, for example – that show that greater side effects mean a strong immune response.” But that’s not the case with the new crown vaccine; everyone gets roughly the same immunity.
To explain why this is so, it is necessary to understand how the two parts of the immune system work together. The first part is called the innate response and includes those bodily reactions that act like chemical alarms. The other part is the adaptive response, which learns and then remembers how to fight infection by designing B cells that produce antibodies to find and destroy viruses, and T cells that kill any virus-infected body cells. Professor Riley says, “It’s this early immunity to innate responses that changes with age and differences between people, and that’s what determines whether you have more or less side effects to the vaccine.”
“You just need a little bit of an innate response to wake up the adaptive response and get the full complement of B and T cells that can give you protection.”
Is the vaccine mix safe and effective?
For vaccination with the new crown vaccine, if two doses are required, the same vaccine is usually used twice, for example, if the first dose is given by Pfizer, then the second dose is still Pfizer. However, in the past few weeks, scientific teams in Hong Kong and the UK have started to study the mixing and matching of different vaccines, such as using Pfizer for the first dose and AstraZeneca for the second.
Is it safe to mix and match vaccines? What serious adverse reactions may occur? Can immune efficacy be maintained or even enhanced, such as longer duration of immunity, broader targeting, and effectiveness against newly emerged mutated strains? Will unexpected reactions be triggered?
If vaccine mixes were feasible, how much flexibility would it provide to countries for universal vaccination programs? How much of a boost would it be?
These are the main answers that mix-and-match studies are looking for.
The fundamental goal of similar studies in different regions is to try to determine whether vaccine mixes are possible, but the difference lies in which vaccines are mixed, and in the combination of different vaccines and different intervals.
A team from the University of Southampton and the University of Oxford launched a year-long “mix and match” study in April. Adults who have already received their first dose of vaccine, whether from Pfizer or AstraZeneca, can apply to volunteer for the Com-Cov project. The mix can be the same vaccine as the first dose, or it can be AstraZeneca or Pfizer, Modena, Novavax, or some kind of mix.
Once the feasibility of a mix and match vaccination has been established at the scientific level, government departments can then determine the extent to which the adoption of such a program would allow for more flexibility and rapid advancement of the vaccination program, both nationally and internationally.
Similar studies are being conducted in China and Russia, based on the same theoretical assumptions: that different vaccine types may work better to stimulate an immune response in different ways with greater confidence in their safety.
Both Hong Kong and China are experimenting with third doses of vaccines or different combinations of two different technical types of vaccines.
In an interview with the BBC, Professor Jeremy Brown of the UK Joint Committee on Vaccines and Immunisation said that, realistically, this (mixing and matching) will become mainstream in the next few years; it is difficult to guarantee two doses of the same vaccine.
How much protection do vaccines offer?
Vaccines do not provide 100 percent protection, nor do they guarantee that you will not contract or spread the virus after vaccination.
Deborah Dunn-Walters, professor of immunology at the University of Surrey in the UK, explains that vaccines act on the body’s acquired immune system, also known as acquired immunity.
This system initiates an immune response against a specific pathogen by recognizing the viral disease through contact with the pathogen, and by stimulating the body to produce immune cells, some of which produce antibodies against the virus. This process takes some time.
The main reason why it is still possible to contract and transmit the new coronavirus after vaccination is that vaccine efficacy is assessed primarily by looking at the presence or absence of symptoms after vaccination rather than the presence or absence of infection, and asymptomatic infection is a hallmark of the new coronavirus.
She noted that there is no evidence that existing vaccines, whether one or two doses, can stop the spread of the virus.
Most vaccines require two doses to be fully administered, as it is the second dose that triggers the second phase of the immune response and creates long-term immunity.
Danny Altmann, professor of immunology at Imperial College London, calls it triggering the autoimmune function into a new fine-tuned mode.
When the body’s immune system first meets the vaccine, it activates two important types of white blood cells (leukocytes): B plasma cells, whose main function is to produce antibodies, and T cells, whose lifespan is short, and whose number decreases dramatically after a few weeks without a second dose of the vaccine.
T cells, also called T lymphocytes, differentiate into different effector subtypes after maturation and are able to recognize and kill different pathogens, one of which is called memory T cells, which can survive for decades in the body if they do not encounter the target (virus).
The key is that these memory T cells are only produced in large numbers after the second vaccination.
As to how long between vaccinations should be, there still seems to be a possibility of change. Pfizer and Modena popularized vaccination in the UK initially with three weeks between doses, which later became three months apart.
There is no definitive answer to the question of how long the first dose of vaccine provides immune protection. Further complicating matters is the fact that the effectiveness of the vaccine may vary from person to person.
The European Medicines Agency (EMA) said on April 7 that rare blood clots should be classified as a very rare side effect of the Oxford/AstraZeneca vaccine, but it is not possible to determine whether risk factors such as age or gender are relevant. immune response” to the vaccine.
This is similar to what happens in people treated with the drug heparin. Heparin is a blood thinner used to prevent thrombosis, and in some cases, a potentially dangerous immune reaction to the drug has led to a condition known as heparin-induced thrombocytopenia.
The development of thrombotic symptoms is also one of the rare side effects of oral contraceptives.
As of March 22, 25 million people in Europe had received the AstraZeneca vaccine and 86 cases of blood clots had been recorded, mostly in women under the age of 60, including 18 fatal cases.
The U.S. Food and Drug Administration (FDA) said in mid-April that it found six cases of blood clots after more than 6.8 million doses of the vaccine in the population, all in women between the ages of 18 and 48, who developed symptoms of blood clots on days 6 to 13 after vaccination.
How long does the vaccine remain effective?
The efficacy of different vaccines varies between mild cases and severe cases requiring hospitalization. The “efficacy” in a laboratory setting may differ from the “effectiveness” produced in practice.
In practice, the “efficacy” of a vaccine may be influenced by the age, physical condition, and presence of disease of the vaccine recipient.
Since both the virus and the vaccine have not been available for a long time, it is difficult to extrapolate the medium- to long-term efficacy of the various vaccines, but it is generally believed that they can provide immune protection for roughly six months to one year.
In early 2021, the La Jolla Institute for Immunology in California published a study reporting that autoimmunity can be maintained for at least six months after a person has recovered from a new coronavirus infection. Public Health England found that it was at least 5 months.
The immunity provided by the vaccine is roughly the same as the immunity that occurs naturally after infection, but the duration varies depending on the individual’s body type and health status.
Julian Tang, a virologist at the University of Leicester in the United Kingdom, said vaccine immunity lasts roughly 6-12 months, but much depends on the individual and the type of vaccine.
Andrew Badley, a professor of molecular medicine at the Mayo Clinic, believes that the effectiveness of vaccines and immunity may last for several years, but that it is important to closely monitor cases of mutant strains of infection and the response of patients after vaccination.
How can immunization vaccines save lives?
How do different vaccines compare?
It is difficult to simply compare the advantages and disadvantages.
Some vaccines are more effective in immunizing against minor illnesses than protecting against serious illnesses requiring hospitalization, while others do the opposite; some have more common side effects but less chance of serious ones, while others have fewer common side effects but to a greater degree.
For example, viral vector-based vaccines may cause lymphomegaly, but recombinant protein vaccines do not show this reaction.
Beyond this, comparisons between vaccines involve a variety of factors such as storage, transport, dose and frequency of administration, availability and price. There are many other considerations that governments take into account when developing their own vaccination rollout plans, including cost, politics and diplomacy.
The new crown epidemic: a group of volunteers who risked their lives to help accelerate vaccine development
Both the Modena and AstraZeneca vaccines stimulate the immune response of human cells to the New Coronavirus through messenger ribonucleic acid (mRNA), but this messenger ribonucleic acid is so fragile that it can split and fail at slightly higher temperatures, so it needs to be injected with a protective layer of lipid nanoparticles and stored at ultra-low temperatures.
Other types of vaccines require only conventional low-temperature storage, which has a longer shelf life and is easier to transport.
The effectiveness of existing vaccines against mutated strains is a major concern for both the research and development community and the public.
The Modena vaccine developer says this vaccine is also effective against emerging mutant viruses in the UK and South Africa, but is developing new vaccine components to improve protection.
The Pfizer/BioNTech vaccine also says it is effective against new mutant strains.
Overall, governments and public health agencies will be watching closely for the emergence of new mutant strains of the virus and assessing the effectiveness of existing treatments and vaccines.
Andrew Badley, a professor of molecular medicine at the Mayo Clinic Medical Center, said there is no 100% effective vaccine; the degree of protection from a vaccine depends heavily on the mutation of the virus.