Why Still Infected With The Delta Variant After Vaccination?

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Why Still Infected With The Delta Variant After Vaccination?

A few days ago, the World Health Organization (WHO) announced a set of worrying figures-in the past week alone, the WHO has received more than 4 million reports of COVID-19 cases. Among the six WHO working regions around the world, five regions have experienced an increase of more than 80% in the past four weeks. According to the current trend, in the next two weeks, the cumulative number of global COVID-19 cases will exceed 200 million.

The main culprit for this epidemic is the Delta variant that has recently raged around the world. The frightening thing is that among the currently known cases of Delta variant infection, there are many individuals who have been fully vaccinated. Does this mean that the COVID-19 vaccine has failed? Does vaccination still work? In the face of a seemingly endless epidemic, how can we protect ourselves?

Dangerous Delta Variant Multi-party data shows that the Delta variant is "unusual" compared to the previous variants. According to a CDC internal communication document recently published by the Washington Post, the infectivity of the Delta variant is much higher than that of the original strain-it is more infectious than the common cold, seasonal flu, the 1918 flu and smallpox, are close to the level of chickenpox.

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▲The transmission power of the Delta variant has surpassed the smallpox and the 1918 flu (picture source: reference [1])

There are many reasons for the increased infectivity of Delta variants. A study recently released by the Guangzhou Centers for Disease Control and Prevention analyzed a series of Delta variant infection cases found in China. It was found that infected people took an average of just four days to test positive for nucleic acid after their first exposure to the virus, a full two days less than the six days in 2020.

And based on nucleic acid testing data, it is estimated that people infected with the Delta variant have a viral load 1,260 times higher than those infected with the original strain when they first test positive. The report on this paper in the journal Nature pointed out that higher viral load and shorter incubation period can explain why the Delta variant has increased infectivity.

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In addition, a study from Singapore found that the Delta variants took longer to shed the virus, with a median of 18 days. In contrast, the original strain is only 13 days old. This also means that once infected with the Delta variant, it can cause infection for a longer time.

In terms of danger, data from Canada, Singapore, Scotland and other places show that the Delta variant may cause more serious symptoms, such as being more likely to be hospitalized, more likely to enter the ICU, and more likely to die.

Some unpublished preliminary data from the CDC indicate that the vaccine does not seem to have sufficient protection for the Delta variant. In a recent outbreak in Massachusetts, there was no significant difference in viral load among people whether they had been vaccinated or not. Does this mean that the vaccine is no longer effective?

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Has The Vaccine Expired?

An expert on communication research mentioned that in the early days of the vaccine, excellent data made the public feel that it was the best choice to completely eliminate the epidemic. And this is an over-reassurance to some extent, so when people find that they are still infected with the COVID-19 after being vaccinated, it is easy for everyone to lose confidence in the vaccine and think that the vaccine has expired.

But this is not a rational thing to do. Because in the terms of reducing the severity of the disease, the effect of the vaccine is still quite obvious.

Data from the world shows that in England/Scotland, Canada, Israel and other places, Pfizer's mRNA vaccine does have a certain degree of reduced efficacy in the face of the Delta variant. But this is mainly reflected in "confirmed infection" and "symptomatic disease." In the "hospitalization or death", the vaccine can still provide a higher protective effect.

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▲Compared with the vaccinated group (blue), the unvaccinated group (green) has a much higher risk of infection, hospitalization, and death (picture source: reference [1])

In fact, this is exactly what the vaccine does. Although the effectiveness of vaccines in preventing infection and transmission may decrease, it can still prevent more than 90% of serious diseases.

On the contrary, if not vaccinated, the risk of contracting COVID-19 is 8 times that of the vaccinated person, and the risk of hospitalization and death are 25 times that of the vaccinated person.

In other words, the recent ravages of the Delta variant, the surge in COVID-19 cases, and the breakthrough infection in the vaccinated population have not declared that the COVID-19 epidemic has gone out of control. We need to be aware of what the vaccine can do instead of treating "zero infection" as the only criterion. From the point of view of effectiveness, the biggest effect of vaccines is to reduce hospitalizations and deaths, followed by reducing the emergence of diseases, and finally reducing infections. If you are infected, you don't necessarily get sick (such as asymptomatic infection), or if your condition is not serious after getting sick (no need to be hospitalized), it is actually a great protection.

Based on the protection data of the vaccine and the characteristics of the Delta variant, a reasonable expectation is that we will hear more cases of breakthrough infections and see more community-based transmission, even as more people are

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vaccinated.

Considering this situation, vaccines are not the only means to control the epidemic. In addition to vaccination, we also need to adopt other non-drug interventions, such as wearing masks. A model shows that, considering the high infectivity of the Delta variant and the penetration rate of the vaccine, wear a mask would be enough to significantly control the spread of the virus.

Conclusion In summary, the combination of data from multiple sources does not indicate that the Delta variant has rendered the vaccine ineffective. These objective data tell us what kind of protective effect the vaccine will have in different situations, and also tell us how to better protect ourselves under the premise that the Delta variant is raging. This not only requires us to make changes in behavior (such as wearing masks), but also requires us to make changes in mentality. With the coexistence of vaccines and COVID-19 variants, we need to focus on whether we can reduce severe cases and reduce the medical burden, rather than worry about whether the COVID-19 can be detected in the individual's nose.

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References: [1] Improving communications around vaccine breakthrough and vaccine effectiveness. Retrieved August 1, 2021 [2] ‘The war has changed’: Internal CDC document urges new messaging, warns delta infections likely more severe, Retrieved August 1, 2021 [3] One number could help reveal how infectious a COVID-19 patient is. Should test results include it? Retrieved August 1, 2021 [4] Clinical and Virological Features of SARS-CoV-2 Variants of Concern: A Retrospective Cohort Study Comparing B.1.1.7 (Alpha), B.1.315 (Beta), and B.1.617.2 (Delta).

[5] Viral infection and transmission in a large well-traced outbreak caused by the Delta SARS-CoV-2 variant. Retrieved July 18, 2021