April 16, 2024

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Why can vaccinated people still spread COVID-19 Delta variants?

Why can vaccinated people still spread COVID-19 Delta variants?



Why can vaccinated people still spread COVID-19 Delta variants?  The high viral load will last for 1 week. As for why it does not decrease within 1 week, there is no answer yet.


On August 13th, Nature published a news article on the front page: “How do people who have been vaccinated spread Delta? See how science explains it.” In the introduction, Nature pointed out that “the key question still exists (not answered). “.


Why can vaccinated people still spread COVID-19 Delta variants?

(Nature headline today)

A number of studies have pointed out that the Delta viral load has not decreased in the vaccinated population


Nature proposed that the origin of the concern that vaccinators will continue to spread the virus after being infected with the Delta virus is almost the same as the source of information that the “medical community” has been paying attention to before.


The first is the mass infection in Massachusetts announced by CDC at the beginning of the month. In that infection, the viral load of the vaccinated infected person was as high as that of the unvaccinated infected person, which means that the breakthrough infection is the same as the general infected person. Have exactly the same ability to spread the virus. Therefore, the CDC in the United States requires people who have completed the vaccination to wear masks to curb the spread.


Then the Wisconsin Department of Public Health and local colleges and universities jointly issued a study that confirmed the findings of the CDC in the United States-people who were infected with Delta after vaccination had no difference in viral load and those who had not been vaccinated. This study also pointed out that these breakthrough infections are highly contagious, so after vaccination, you must still pay attention to protection to avoid infection and spread of the virus.


Nature emphasized in this headline that the large-scale breakthrough infection in Massachusetts and the non-decreasing viral load of the breakthrough infection were explained by some as “triggered by large-scale aggregation”, but in Wisconsin, This kind of gathering has not been carried out, and there are still similar trends and the result that the viral load does not decrease, so the article suggests that even the gathering of ordinary family groups may still cause the virus to spread at a high speed.



New research from Texas suggests the same problem


In addition, Nature cited a third paper that proved the same conclusion, from Houston, Texas, the following paper-


Why can vaccinated people still spread COVID-19 Delta variants?


The paper also pointed out that patients who were infected with Delta after vaccination had no difference in viral load from those who were not vaccinated. At the same time, this article adds a more detailed control, that is, in the case of non-Delta infection, the viral load of breakthrough infection is significantly lower than that of unvaccinated. In a horizontal comparison, the Delta virus has a breakthrough infection, and its viral load is much higher than that of other viruses. See the table below for detailed data.


Why can vaccinated people still spread COVID-19 Delta variants?


The data on the left side of the table is the data of patients with breakthrough infection after vaccination, and the data of patients who have not been vaccinated on the right. It can be seen that in the case of Delta infection, the viral loads of both parties are similar (Ct: 20.67 vs 20.67), and it is not affected by vaccination or not. In the case of other new coronavirus infections, the viral load has opened up the difference (Ct: 35.77 vs 25.31), and the viral load has obviously decreased after vaccination.


At the same time, it can also be seen that infection with other mutant strains, even without vaccination, has a lower viral load than Delta after vaccination (Ct: 25.31 vs 20.67).


In addition, this article also mentioned that through observations of hospitalized patients, the probability of a breakthrough infection of the Delta mutant strain is three times that of other mutant strains. And the hospital stay of patients is longer than that of patients infected with other mutant strains.



The reason is still unknown, more research is needed


Delta leads to increased infectivity and longer hospital stays, which can be explained by increased viral load. However, there is no reasonable explanation for why the viral load of patients with breakthrough infection after vaccination has not decreased.


Researchers in the Houston paper suggested that it is possible that the infection mechanism of the virus has changed, but there is currently a lack of targeted research on this point.


Nature mentioned in the article that Singapore’s research suggests that there is almost no difference in viral load between the breakthrough infected person and the unvaccinated person who are also infected with Delta within the first week after diagnosis, but after a week, the vaccinated person The viral load of infected people declines faster than those who have not been vaccinated. Therefore, it is suggested that the vaccine is effective in shortening the course of the disease and preventing severe illness.


In addition, a statistical survey conducted by Imperial College in the United Kingdom showed that in a large sample size survey that relied on self-reporting by the population, there was a slight difference between the viral load of the breakthrough infection and the unvaccinated. This may suggest that if a larger sample size of the population can be included and more asymptomatic infections can be observed, it may further clarify the current problems.


(source:internet, reference only)

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