Thanks to SARS-CoV-2 we have learned that “change is the only constant”, as Heraclitus sentenced. Humans have been adapting to different changes during this year and a half of the pandemic.
Among these changes, the spread of different variants, which depends in part, but not exclusively, on their genetic differences. These differences arise by pure chance. That is, an error during the replication of the genetic material of the virus causes a mutation.
The accumulation of a certain number of mutations originates a variant, which we call a strain when these changes affect the behavior of the virus.
Delta variant, the most transmissible
In the case at hand in this article, the delta variant (B.1.617.2) has been accompanying us (at least) since December 2020. It has already become dominant in many countries in recent months. In fact, represents more than 96.5% of the last cases diagnosed in Spain.
The rapid and wide spread of this strain suggests that it is more transmissible than the alpha variant (lineage B.1.1.7). Its success appears to be due to very rapid replication and the generation of a 1,000 times higher viral load. Thus would reduce notably the incubation time required for transmission.
More seriousness of the disease?
However still there is not enough evidence to affirm that this strain is more pathogenic. Let us remember, on the one hand, that this variant supposed a increase in the probability of hospitalization in the UK.
But on the other hand, the information available from the Public Health England (PHE) suggested that the case fatality rate (CFR) for this variant was lower that of the alpha variant.
However, these comparisons between variants are complex and probably inadequate. Regardless of your genetics, variants expand at very different times of the pandemic.
In addition, there are multiple factors at play, such as the saturation of the health system, the vaccination status and the age of the infected people, which makes it really difficult to deal with them.
How the vaccine reacts
Now more than 70% of the Spanish population has the complete vaccination schedule. Therefore, it is worth wondering if these vaccines still protect us against the delta variant or if, as has been speculated, we are more contagious despite being vaccinated.
To resolve this debate, we must first distinguish between protecting ourselves from being infected and protecting ourselves from serious disease.
We knew that when delta was not the dominant variant, vaccines licensed so far had been very effective to prevent serious pathologies, hospital admissions and deaths.
But now a study concludes that the vaccine efficacy of AstraZeneca against serious diseases caused by delta is 67% (74.5% against alpha), while that of Pfizer would be around 88%, (94% versus alpha).
Other study conducted in South Africa indicates that Johnson & Johnson’s Janssen vaccine has 71% efficacy against hospitalizations with the delta variant.
However, this vaccine efficacy is notably reduced if the vaccination schedule is not complete. With this, the level of protection against mild pathology is also somewhat lower with the delta variant.
Who does the vaccine protect?
We also know that being vaccinated does not prevent us from becoming infected with the virus. Therefore, these vaccines do not stop transmission. In fact, according to ad CDC, viral load (measured as amount of genetic material of the virus by PCR after nasopharyngeal swab) was identical in vaccinated and unvaccinated infected with this variant.
This study raised the alarm because with this information, the vaccinated infected, asymptomatic in many cases, preventive measures should be taken to prevent transmission. Ultimately, they should continue to act as if they were not vaccinated, with all that that implies.
Upon review of these studies, it appeared that these vaccines only functioned as a “seat belt.” In other words, they reduced the damage if we suffered an accident but did not prevent us from suffering such an accident (infecting ourselves and transmitting the delta variant of the virus to other people).
We are no more contagious
However, we now have several pieces of evidence that vaccines don’t just offer personal protection. The first comes from a study in which it is corroborated that those vaccinated had the same amount of genetic material than those not vaccinated, but only during the first five days after the onset of symptoms. From that point on, the viral load falls much faster in vaccinated individuals.
But determining the viral load as the amount of genetic material of the virus is not the most accurate way to determine the amount of viable and infectious virus.
Therefore, when using samples from people mainly infected with the delta variant and carrying out infection assays of cell cultures, it has been proved that the infectious capacity of the virus is much lower if the person was previously vaccinated (con Pfizer o Johnson & Johnson).
Finally another study has confirmed that the infectious virus shedding period (also determined by infection of cells in culture) was significantly reduced in vaccinated compared to unvaccinated individuals, in this case when alpha was the dominant variant.
Ultimately, these studies, which must pass the peer review process (that is, they are not yet final), suggest that people infected with the delta variant (or with the alpha variant) transmit fewer infectious viruses and do so for a shorter period if they have received the vaccine, even if their ability to transmit the virus is not null. So, for now, it is recommended that you follow the rules that prevent transmission.
* This article was originally published on The Conversation.
** Salvador Iborra is a professor of Immunology and Infection at the Complutense University of Madrid.
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