June 14, 2024

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Can the vaccine prevent the super spread of COVID-19 Delta variants?

Can the vaccine prevent the super spread of COVID-19 Delta variants?



Can the vaccine prevent the super spread of COVID-19 Delta variants? The vaccine still needs to be given to reduce severe illness and hospitalization. 


Recently, the United Kingdom reported a set of “seemingly contradictory data” on whether it will catch the virus and infect others after the COVID-19 vaccine.


On August 6, local time, the Public Health England (PHE) stated that preliminary data showed that in the delta variant infection, the viral load of those who had received two doses of the vaccine was comparable to that of those who had not been vaccinated. This may mean that the ability of an infected person to spread the virus to others is the same regardless of whether they have been vaccinated or not. There is a similar statement in the internal documents exposed by the Centers for Disease Control and Prevention (CDC) of the United States.


But just two days before the release of the PHE data, the “National New Coronavirus Infection Tracking Study” REACT-1 led by Imperial College in the United Kingdom announced the latest round 13 analysis. The results show that vaccination can effectively reduce the viral load discharged by the infected person, so it is not easy to infect others.


However, the data disclosed in related studies is still incomplete, and it cannot simply be said that the protection of vaccines has decreased or the risk of virus transmission has increased.




What did the two studies in the UK say?


The British “Daily Mail” made preliminary reports on both PHE and REACT-1. The article shows that the time frames covered by the two studies are close, and both focus on breakthrough infections after vaccination. The result may reflect to a certain extent that “vaccine cannot stop the spread of the virus.”


PHE uses the UK’s hospitalized cases of COVID-19 since July 19 as the research object. During this period, the delta variant has become the main epidemic strain in the UK.


The REACT-1 project invites subjects to take samples at home and send the samples back to the laboratory for nucleic acid testing. The project analyzed 98,233 samples collected from June 24 to July 12 this year. Genetic sequencing of 254 of the samples revealed that they were all Delta mutants.


Second, both studies analyzed the Ct value (cycle threshold value).


The Ct value is translated as “cycle number threshold” and refers to the value measured after the new coronavirus gene has passed the viral nucleic acid test (PCR) in a laboratory environment.


“Health and Health Magazine” quoted Shi Xinru, director of the Center for New Virus Infection Research of Chang Gung University, Taiwan, as saying that the new coronavirus is very small, about 1/10 of the influenza virus. Therefore, to measure the RNA concentration of the new coronavirus, specific genes need to be replicated multiple times and amplified by PCR. When the Ct value=1, the virus can be observed twice as large as it is amplified. Ct value=2, it is magnified 2×2 times. And so on.


The concentration of viral RNA is inversely proportional to the Ct value. If the concentration is high, PCR can be observed with fewer copies, and the Ct value is lower. On the contrary, when PCR must be replicated many times to observe the viral RNA concentration, the Ct value is relatively high. A number of studies have shown that infected persons with higher Ct values ​​are less likely to get sick and spread the virus.


PHE analysis stated that among the unvaccinated people, the average daily Ct value of those infected with the delta variant strain was 17.8. At the same time, a fully vaccinated person has an average daily Ct value of 18 after being infected with Delta. In view of the similar Ct values, PHE inferred that the ability to infect others is the same whether or not vaccinated.


REACT-1 showed that the same Delta mutant strain infection, the average Ct value of the vaccinated people was 27.6 (25.5, 29.7), and the non-vaccinated people were 23.1 (20.3, 25.8), “the viral load excreted by the infected Significantly lowered.”


“Pay attention to the ‘daily average’ and ‘average’ here. We have to look at it together with the time axis of virus discharge.” Professor Jin Dongyan explained, assuming that the time window for vaccinated people to release the virus is 2 days, and the time window for those who have not been vaccinated is In 5 days, although the Ct peak is similar, the time for the former to spread the virus is significantly shortened, so the risk of infecting others will naturally decrease.


“You cannot simply convert the Ct value into clinical infectiousness.” Stephen Evans, professor of drug epidemiology at the School of Hygiene and Tropical Medicine, University of London, UK, has a similar statement. He told the “Daily Mail” that the Ct value measured by the study may originate from different stages of the infection and cannot be directly compared.


Moreover, REACT-1 relies on the people to detect and submit data independently, and there are many uncontrollable circumstances. The number of PHE subjects is unknown, and the time and frequency of nucleic acid testing is also unknown. Even PHE itself admits that these deficiencies may distort the average Ct value.


“The ideal state is to continue the test for a period of time when the virus is positive,” said Professor Jin Dongyan.




The dispute of Ct value


“Health and Health Magazine” pointed out that the Ct value is used to evaluate the transmission power, which is controversial.


First, it is limited by the amount of virus in the sample taken, not the total amount of virus in the human body, and it is not equal to the amount of live virus. Clinical experience has shown that the Ct value is between 30-35, and some people are positive for virus isolation and culture, that is, live virus can be cultivated. But some are not. The abnormal Ct value may be due to the residual viral nucleic acid fragments in the body, and the infectivity is almost zero.


Secondly, it also changes due to different equipment and reagents used.


Finally, the Ct thresholds set by different countries and regions are different. On June 24 this year, a female student from Taiwan, China, was tested locally, and after obtaining a “COVID-19 nucleic acid negative” certificate, she took the flight to Japan. When entering the country, she detected a Ct value of 37.38 and was sentenced to be positive for COVID-19.


The Epidemic Command Center in Taiwan explained that this is because “everyone does not have a unified Ct value standard.” Taiwan, China regards Ct value <35 as a clear diagnostic criterion, and the infected person has the ability to transmit. If the Ct value is between 35-40, some medical institutions will do a second test.


In Malaysia, Japan and the United States, the Ct value = 40, which is regarded as a “positive line”.


Professor Jin Dongyan emphasized that the low Ct value and high dissemination have become common sense. Setting the Ct threshold high (40) can be understood as “holding tighter”.


Jenny Harris, chief executive of the British Health and Security Agency, said that the PHE data gave a reminder to the academic community that the COVID-19 vaccine does not eliminate all risks, and it may still be infected with the COVID-19 virus and spread to others after vaccination. “But next, we need to further study whether the Ct value of a breakthrough infected person will affect the spread of the virus after being infected with the delta mutant.”


Partial results have been given in advance of a study by more than 15,000 medical staff in Israel. “Intellectuals” stated that the study found more than 20 cases of breakthrough infections. The Ct values ​​of some breakthrough infections seemed “possible to spread”, but in the end they were not found to further infect others.


“PHE data shows that 55.1% of hospitalized cases are people who have not been vaccinated.” Stephen Evans said, this shows that the vaccine is effective, but not 100%.





(source:internet, reference only)

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