The Centers for Disease Control and Prevention (CDC) (the US Center for Disease Control and Prevention) says that the chance of an unvaccinated person contracting the coronavirus is approximately five times greater than a person who has already been fully vaccinated.
This number, calculated in the United States, is taken from a scenario in which the delta already corresponds to most cases of Covid, as is also the case in some Brazilian states and cities.
If the strain has not yet spread, the risk of an unvaccinated person becoming infected is, on average, 11 times higher compared to someone who has completed a course of vaccination.
With this data, the Centers for Disease Control and Prevention (CDC) says, the ability of vaccines to stop virus transmission decreased with the spread of the delta, but it still provides a very important degree of protection for the population, especially for severe cases of the disease.
The agency reiterates that even with Delta, unvaccinated people are about ten times more likely to be hospitalized than those who have already been vaccinated — in the case of deaths, that number rises to 13.
The researchers then concluded that the progression of the variant in the United States was an important factor in explaining the increased rate of Covid-19 prevalence among vaccinated people. However, the strain did not have a significant effect on the increase in severe cases of the disease for those who were vaccinated.
The study also notes that although the number of cases has increased for those who have been vaccinated, infection rates are still higher among those who have not been vaccinated.
This information is part of a survey that analyzed the impact of the strain in the United States considering the Pfizer, Moderna and Janssen vaccines. In the survey, the CDC examined more than 600,000 patients over the age of 18 in 13 US states.
The center divided the study into two periods in 2021. The first was from April 4 to June 19, when the delta was not responsible for most injuries. The second begins on June 20 and ends on July 17, during which time the variant was already prevalent, reaching 90% of all SARS-CoV-2 diagnoses.
Using this model, the researchers compared the periods and were able to estimate the difference in transmission, hospitalization, and death before and after delta spread.
According to the survey, there was a 13 percentage point increase in Covid-19 cases among fully vaccinated individuals in the predominance period of the strain. The estimate was that without the variable, these diagnoses would have increased by only five percentage points.
The scientists also looked at the two ranges in an effort to understand how low the effectiveness of vaccines could be.
In the case of being able to stop transmission of the Covid-19 virus, the research found that protection was close to 91% before delta spread – a number that has fallen to 78% due to the prevalence of the variant which explains the cause of cases in vaccinated people. increased.
However, the Centers for Disease Control and Prevention states that on the dates of the strain’s largest spread, there was only a two and three percentage point decrease in vaccine efficacy for hospitalizations and deaths, respectively—evidence of the full extent of immunization. The strategy is still more effective against Covid.
In the research, analyzes were also performed by different age groups. The participants were divided into three groups: 18 to 49 years old, 50 to 64 years old and over 65 years old.
Across all scales, there has been an increase in vaccinated people who contracted the Covid-19 virus, which is already to be expected when vaccine coverage increases.
In the delta prevalence scenario, it was evident that all ages experienced a more than expected increase in the number of cases – an example being injuries in people aged 50 to 64 years, which nearly quadrupled during the second period of the study.
However, only in the category of those over 65 who had already been vaccinated, in addition to the increase in the number of cases, was there an increase in hospitalizations and deaths with prevalence of the variant.
Regarding unvaccinated people, the researchers claim Delta caused more Covid-19 diagnoses, in both mild and severe cases, regardless of age group.
Paulo José da Silva, Professor at the Department of Applied Mathematics at Unicamp (Campinas State University), stresses that in Brazil, too, full vaccination is proving to be very important to stop serious cases of Covid-19 caused by Delta.
He conducted a study with a mathematical model that estimated the effectiveness of the AstraZeneca vaccine against Covid-19 in different scenarios. One of these tests indicated that in a delta-like situation, it is important to introduce the second vaccination dose to avoid further infection and severe illness.
“What the research teaches us today is this: the second dose is very important, more important than it was before, because the delta came with this property, at least that is the first information we have, which is the ability to evade defenses. That we only have one dose,” he says. Silva says.
In Brazil, deltas are already present in all states, says Fernando Spielke, coordinator of the Corona-ômica BR-MCTI Network, a project that sequences the genomes of samples of the SARS-CoV-2 virus. Most of these diagnoses are found in the south and southeast of the country.
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