From mutant strains Alpha, to Beta, to Gamma and Delta, the Delta strain has become the dominant strain of the new coronavirus due to its higher viral load and shorter incubation time, and is now the predominant strain in most parts of the world.
The Delta strain is detectable 4 days after exposure, while the average time for the original strain to be detected after exposure is 6 days, meaning that the Delta strain replicates much faster. The danger of the Delta strain has countries around the world on alert.
However, what is more worrisome than the danger of the virus is that although the New Coronavirus vaccine is currently one of the most beneficial weapons in the fight against NCP, it appears to have broken through the vaccine barrier to some extent as mutated strains continue to emerge. The vast majority of confirmed cases in the Nanjing outbreak due to the Delta strain have already been vaccinated.
Why do you still get infected after vaccination? What adjustments do vaccination strategies need to undergo in the face of new strains of coronaviruses?
Is the vaccine not 100 percent effective?
The mechanism of action of the vaccine is the reason why the vaccine is still infected after vaccination. The mechanism of action of the Neocrown vaccine is the principle of immunity. The neo-crown vaccine is a modified form of the neo-crown virus or part of the neo-crown virus, and when the body is vaccinated, for example, by injection, immunity occurs, followed by the production of protective antibodies and immune memory. This process then takes some time.
And, most vaccines require two doses to be fully administered, as it is the second dose of the vaccine that stimulates the second phase of the immune response and produces long-term immunity, such as the MMR (MMR). Studies have found that 40% of those who received only one dose were not fully immune to the three viruses, compared to 4% of those who received a second dose.
The reason for this is that the follow-up booster stimulates the immune system to enter a new fine-tuning mode: the body’s immune system activates two important white blood cells when it first meets the vaccine: B plasma cells and T cells, whose main function is to produce antibodies, but which do not live long enough to cause a sharp decrease in the number of antibodies if a second dose of the vaccine is not given.
In addition, different vaccines have different levels of efficacy. The “efficacy” in a laboratory setting may differ from the “potency” produced in practice. In practice, the “efficacy” of a vaccine may be influenced by the age, physical condition, and absence of disease of the vaccine recipient.
In early 2021, the La Jolla Institute for Immunology in California published a study that showed that autoimmunity can be maintained for at least 6 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. According to Julian Tang, a virologist at the University of Leicester in the United Kingdom, the vaccine provides immunity for about the same amount of time as the natural immunity after infection. Julian Tang, a virologist at the University of Leicester in the United Kingdom, said that vaccine immunity lasts roughly 6 to 12 months, but much depends on the individual and the type of vaccine.
It’s easy to see that there are a variety of factors that affect the effectiveness of a vaccine. In this context, researchers have tried to identify criteria that would allow them to assess the protective efficacy of the new crown vaccine.
In an article published in NEJM on July 28, local time, entitled Covid-19 Breakthrough Infections in Vaccinated Health Care Workers, researchers from Israel suggest that vaccine-induced neutralizing antibody levels may be a predictor of whether a vaccinated person will contract SARS-2. CoV-2. Those with lower levels of antiviral antibodies were more likely to be infected with the new crown.
The researchers initiated the study with about 11,500 health care workers who had completed two doses of the Pfizer mRNA vaccine. Of the 1,497 healthcare workers tested by RT-PCR, 39 were confirmed to be infected with SARS-CoV-2, the majority of whom were women (64%), and the median interval between completion of vaccination and testing was 39 days for all infected individuals.
The researchers then compared available neutralizing antibody data from 22 cases detected during the infection period with data from 104 participants and found that the former data were significantly lower than the latter, with predicted geometric mean titers (GMT) of 192.8 and 533.7, respectively, and lower GMT for S-specific IgG antibody levels in the infected group than in the control group, with a ratio of about 0.514 between the two.
This seems to reveal the reason for the difficulty of the vaccine in helping some of the population to fight off the virus, with people with lower levels of antiviral antibodies apparently having a greater likelihood of contracting the new crown. At almost the same time, the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, in conjunction with Moderna, came to a similar conclusion about the critical role of neutralizing antibodies in helping to ward off SARS-CoV-2 infection.
Overall, however, numerous lines of evidence point to the fact that vaccines do not provide 100 percent protection, nor do they guarantee that the virus will not be contracted or transmitted after vaccination. This, of course, does not detract from the fact that vaccines remain the most effective means of controlling the new crown outbreak.
Vaccination is still a must
In the face of an epidemic of the Delta strain, the effectiveness of the vaccine is of great concern. After all, the vast majority of confirmed cases of infection due to the Delta strain in the Nanjing outbreak have already been vaccinated, which is a cause for concern. It is worth noting that although vaccines do not provide 100% protection, various vaccines have shown high protection against mutated strains of the new coronavirus.
A week ago, the NEJM published the latest study from the UK Department of Public Health. A large case-control and viral sequencing analysis of more than 4,000 cases of Delta mutant infection showed that two doses of the New Coronavirus vaccine provided up to 88.0% protection against symptomatic infection with the Delta mutant strain, a modest reduction in protection compared to the previously widespread Alpha mutant strain in the region.
The team evaluated the effectiveness of different new coronavirus vaccines against symptomatic new coronavirus disease (COVID-19) caused by the Delta mutant strain compared to the Alpha mutant strain, based on data from the period when the Delta mutant strain became endemic, up to mid-May.
A total of 19,109 symptomatic ≥16 years old cases were included by the data, who were sequenced to confirm infection with the Alpha mutant strain (14,837 cases) or Delta mutant strain (4,272 cases) and who had been vaccinated with BNT162b2 or ChAdOx1 nCoV-19 vaccine according to the procedure. Data from the population that had been tested negative during the same period were also compared.
Analysis of vaccine efficacy showed that both vaccine doses showed high protection against the Delta mutant strain. Two doses of BNT162b2 vaccine were 93.7% effective in preventing symptomatic infection with the Alpha mutant strain. In comparison, the effectiveness against symptomatic infection with the Delta mutant strain was 88.0%, which was not a significant decrease.
For the other new crown vaccine, ChAdOx1 nCoV-19, the effectiveness of two doses of ChAdOx1 nCoV-19 against symptomatic infection with the Delta mutant was 67.0%, again with a modest decrease compared to the effectiveness against the Alpha mutant (74.5%).
And, the data also suggest the importance of complete vaccination. With a single dose of BNT162b2 vaccine, the effectiveness against symptomatic infection with the Delta mutant (30.7%) was significantly lower than that against the Alpha mutant (48.7%). Similarly, the effectiveness of prevention of symptomatic infection with the Alpha and Delta mutant strains was 48.7% and 30.0%, respectively, when only one dose was administered. The difference in protective effect was even more pronounced.
This is because the body’s immune system activates two important types of white blood cell leukocytes during the initial encounter with the vaccine. The first is the B plasma cell, whose main function is to produce antibodies. However, they do not live long, and the body has a large number of antibodies for the first few weeks after the initial vaccination, while the number of antibodies decreases dramatically without the second dose of the vaccine.
Moreover, the second dose of the vaccine initiates the process of “B-cell maturation”, after which the B-cells, which are the “elite force”, enter the spleen and complete their development there. This means that the booster vaccine not only increases the number of B cells, but also produces more accurate antibodies to kill the enemy.
The other type is T cells, also known as T lymphocytes, which can recognize and kill different pathogens. One type, called memory T cells, can survive for decades in the body if they don’t encounter a virus. This means that some vaccines can provide lifelong immunity. The key, however, is that this T-cell is only produced in large numbers after a second vaccination.
Therefore, vaccination requires a second exposure of the body to the antigen, the molecule on the pathogen that triggers the immune system, through a follow-up vaccine booster injection, which activates the second phase of the immune response.
In addition, in terms of delaying the disease, a phase III clinical trial conducted in the UAE showed that Sinocrown inactivated vaccine from Sinopharm reduced the need for hospitalization by 93% and the need for intensive care units by 95% in infected patients. These data show that even when infected with the virus, vaccination can significantly reduce the rate of serious illness and death.
Another domestic inactivated vaccine, kerafol, also has excellent post-infection protection. Although its efficiency in preventing infection is only 50.65%, it can keep 66.97% of infected patients from showing obvious symptoms and 100% of infected patients from developing serious illness. In addition, our adenovirus vector vaccine “Kvisa” can also reduce the rate of severe disease by 90.98%.
Even for viral subtypes that are highly transmissible, such as the delta mutant, the existing vaccine can significantly reduce the rate of severe illness and death. delta virus does not have many mutation sites, and although the vaccine-induced antibodies cannot eliminate it, they can temporarily suppress its replication, allowing time for the immune system to reactivate and for drug therapy to work.
With the reality of increasing mutant strains of the virus and further increasing transmission, vaccination remains one of the most effective means of combating outbreaks. Vaccines may not guarantee us immunity from viral invasion, but they can still help us defeat the enemy and minimize damage.