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More than 12,400 Israeli residents have tested positive for COVID-19 after being vaccinated, including 69 people who had already received the second dose, which began to be administered at the beginning of last week, the ministry reported. Health.
This represents 6.6% of the 189,000 vaccinated people who underwent coronavirus tests after being vaccinated.
According to ministry data, 5,348 people were found infected up to a week after receiving the vaccine, out of 100,000 people who were vaccinated and then tested a week later – an infection rate of 5.4% of those vaccinated during this period.
Another 5,585 people tested positive for the virus between the eighth and 14th day after receiving the first vaccine – 8.3 percent of the 67,000 people who were vaccinated and tested during this post-vaccination period.
People also tested positive more than two weeks after receiving the first dose, between day 15 and day 21, during which time partial immunity is already supposed to be in effect. Of the 20,000 people tested during this post-vaccination period, 1,410 people tested positive, or 7.2%. Of the 3,199 people who were tested for coronavirus between Day 22 and Day 28 after the first vaccine, 84 tested positive (2.6%), including 69 people who had previously been vaccinated twice.
Some 2.15 million people have been vaccinated in Israel over the past month, 300,000 of whom have already received a second dose.
At this stage, it is still difficult to draw definitive conclusions about the effectiveness of the vaccine, for better or for worse. In certain groups of people vaccinated during the different post-vaccination periods, the ratio of positive tests corresponds to the ratio of positive tests in the general population, the overwhelming majority of which had not yet been vaccinated. There could also be issues that most of the people vaccinated first and therefore accumulated the most time after vaccination are over 60 years old.
Meanwhile, serologic tests performed on employees at Sheba Medical Center in Tel Hashomer a week after receiving the second dose of Pfizer vaccine showed that of 102 employees tested, 100 had antibody levels 6 to 20 times higher. than what they had presented a week. earlier.
Sheba’s staff are very encouraged by these results, and according to Professor Gili Regev-Yohai, director of the hospital’s infection prevention and control unit, “It’s exciting. This means that the vaccine is working wonderfully and that we hope to see a drop in the incidence of infection within a few days.
Statistics of infection among those who have been vaccinated in the general population illustrate the importance of the passage of time in building immunity. According to Pfizer, the big jump in immunity is supposed to take place between day 15 and day 21, when the vaccine’s effectiveness is expected to drop from 52% to 89%, after which the second dose is intended to bring the percentage vaccinated to a low. state. 95 percent protection.
But these statistics, encouraging as they are, cannot determine the level of protection that the vaccine gives each person. In addition, the more people are vaccinated, the more likely there will be differences between Pfizer’s results in its clinical trials and results in the field, not only in terms of the level of effectiveness of the vaccine for individuals, but also with regard to its general effectiveness and its capacity to offer “collective immunity”. This is especially true as it is still not clear to what extent the vaccine protects against mutations in the virus.
Israelis aged 60 and over are at this stage the vast majority of those vaccinated “veterans”, who were vaccinated two weeks or more ago. To date, 86 percent of people aged 70 to 79 have been vaccinated, along with 80 percent of those aged 80 or older and 68 percent of those aged 60 to 69. Pfizer had reported that the vaccine had been very effective in people 65 years of age or older, providing 95% protection among 7,000 participants in that age group in its trials. This statistic will have to prove itself in real life, as the immune system erodes over time and becomes less powerful than that of a younger person.
It can be seen in the influenza vaccine, for example, which is less than 60% effective in those 65 and over, while being 80-90% effective in young people, even when the vaccine component is suited to the strains. most common flu types. during a given season.
But age is not the only factor that plays a role. Her immune system erosion can be affected by heredity, lifestyle, exposure to the environment, and more. This is why, over the years, various indices have been developed to separately measure “immune age”.
“The difference in immune responses between people is huge,” says Professor Yoram Reiter, an expert in molecular immunology at Technion – Israel Institute of Technology. “In most cases, we administer vaccines, but we cannot predict the strength of the response or the level of protection, either at the level of antibodies or at the level of cellular protection.”
The most significant difference that is evident to date is the response and side effects experienced by vaccinees aged 55 and under compared to those who are older. The Pfizer trials found that the incidence of side effects differed between age groups.
“This is not unique to the coronavirus vaccine,” Reiter says, noting that the body’s “activation mechanism”, or how the immune system responds a few weeks after a vaccine, is different for younger people. only for the elderly. “In older people it’s usually at a lower level in the first place, which is why exposure to the second dose, which mimics the virus, generates a less potent response. This is why we see fewer reactions or side effects that express the active response of the immune system. ”
However, he stressed, the absence of reactions or side effects does not indicate that the vaccine is less effective or that his immune system is weak.
According to Professor Zvika Granot, an expert in immunology at the Hebrew University Faculty of Medicine, “an elderly person’s immune system is less efficient and this is apparently the reason for the differences in reactions. A 70 year old will react differently to a virus than a 20 year old. The response to the second dose, unlike the first, is already the body’s response to the virus, or in this case the protein produced by the cell that mimics the virus.
He added, “In general, an acquired immune mechanism is less flexible in the elderly and generally less responsive. This means a slower and less powerful reaction. This does not mean that the vaccine is less effective. But this certainly explains why in older people an explosive reaction of the immune system with side effects is less common.
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