Covid-19 and Delta: Viral Load and Vaccine

A thousand times stronger, but not stronger than the vaccine! The Delta variant is in complete conquest of Europe, thanks to a very high infectivity, about 80% stronger than Alpha, which was already more contagious than the traditional strain of coronavirus. In France, for example, the number of contaminations caused by this type almost doubles every five days, according to the latest weekly update from Public Health France. Whereas in the summer of 2020 this doubling time was around 16 days. A significant acceleration that would be due to a much higher viral load (more than a thousand times more!), and not to evading immunity that would allow it to infect vaccinated people.

Strong and fast viral replication

According to a Chinese study (so not yet validated by peers) published in pre-print on July 23, 2021, people infected with the delta variant had a detectable viral infection from the fourth day after infection, compared with six days for the conventional strain. is loaded. Furthermore, the viral load at the time of the first PCR test (hence 4 days for delta and 6 days for the second line) was approximately 1,260-fold higher in those with the variant! At this stage this amount of virus would be enough to allow 80% of Delta’s patients to infect another individual, compared to only 20% for the original strain. These results suggest that Deltas manage to multiply very rapidly inside the patient, making them more contagious before they are detected during the first few days of infection.

Two doses of Pfizer vaccine 88% effective

In addition to this high viral load, the delta variant can evade some monoclonal antibodies. Because of these two features, one might fear that this variant may slip through the cracks of vaccines. Fortunately, we are reassured by epidemiological data from the English Institute of Health (Public Health England), which was published on July 21, 2021 in the journal. New England Journal of Medicine, indicating that two doses of the vaccine are sufficient to neutralize the variant. After analyzing all cases of Covid-19 sequenced in England during the months of April and May 2021 (19,109 in total, including 4,272 with the delta variant), they demonstrated that a single dose of the Pfizer vaccine did not protect 35% , compared to 88% for both doses. On the other hand, this efficacy is lower with the AstraZeneca vaccine (30% and 67%, respectively). Rates are barely a little lower than during infection with Alpha (93.7% for Pfizer and 74.5% for AstraZeneca), which shows us that even if Delta is uptake, it won’t be able to outpace the vaccine.

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About the Author: Abbott Hopkins

Analyst. Amateur problem solver. Wannabe internet expert. Coffee geek. Tv guru. Award-winning communicator. Food nerd.

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