The first study that looks directly at how vaccines prevent the spread of the delta variant is good news and bad news. The good news is that people with the highly contagious SARS-CoV2 mutation are less likely to pass the virus on to others if they have already been immunized with at least one dose of the Covid-19 vaccine. The bad thing is that this effect is relatively small and disappears three months after taking the second dose. The findings increase scientists’ understanding of the impact of vaccination on limiting delta spread, but are “more and more encouraging at the same time,” says Marm Kilpatrick, an infectious disease researcher at the University of California, USA.
Previous research has indicated that people with delta have roughly the same viral loads, regardless of whether or not they’ve been vaccinated. But they also showed that those who have been vaccinated are less likely to spread the virus because their viral loads drop faster than those of unvaccinated people. However, this latest study delved into data from 139,164 close contacts of 95,716 people infected with SARS-CoV-2 between January and August 2021 in the UK, when the Alpha and Delta variants were causing the most infections. The authors found that while vaccines provided protection against infection and transmission, delta infections were attenuated.
But over time, this vaccine’s beneficial effect has diminished to negligible levels. Two weeks after receiving AstraZeneca immunity, people were again transmitting the variant to their close contacts, who, if not immunized, had a 57% chance of infection. Within three months, that number had risen to 67%, the same level as the probability that an unvaccinated person would spread the virus. A decrease in transmissibility was also observed in those vaccinated with the Pfizer-BioNTech immunization agent, by 42% soon after vaccination and 58% over time. says co-author David Eyre, an epidemiologist at the University of Oxford in the United Kingdom. According to Stephen Riley, an infectious disease researcher at Imperial College London, the booster campaigns also raise another doubt: whether the same reduction in protection against infection will occur after the third dose. Only time will give the answer. Below are the vaccination numbers.
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