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September 13, 2021

Vaccinated people are 10 times less likely to be hospitalized by delta variant, CDC says

New studies shed light on the effectiveness of COVID-19 shots

Getting vaccinated against COVID-19 overwhelmingly protects against severe illness caused by the delta variant, according to the latest research from the U.S. Centers for Disease Control and Prevention. But hospitalizations and deaths are more common among fully vaccinated people than they were before the variant arrived. 

A study of 569,142 cases between April 4 and July 17 highlights the powerful effects of the delta variant and the benefits of vaccination. 

Vaccinated people were five times less likely than unvaccinated people to be infected after delta became the most common variant and 10 times less likely to be hospitalized or to die. Delta now accounts for 99% of all COVID-19 infections.

Yet as the delta became predominant, the percentage of fully vaccinated people infected by the coronavirus was higher than expected, researchers said. 

Between April and June 19, fully vaccinated people made up just 5% of COVID-19 cases. If the vaccines had been 90% effective, fully vaccinated people would have been expected to make up 6% of cases. 

But between June 20 and July 17, with delta's prevalence rapidly ascending, fully vaccinated people made up 18% of cases. That mark that would have been expected with a vaccine efficacy of 80%. 

Vaccinated people accounted for 7% of COVID-19 hospitalizations and 8% of deaths in the earlier period. During the latter period, those figures doubled to 14% and 16%, respectively. 

Data was collected through the COVID-19 vaccine breakthrough infection surveillance system, which monitors trends in disease incidence and severe outcomes in fully vaccinated people. Reports from 13 jurisdictions were used for the analysis.

In a smaller study of more than 1,000 hospitalizations, CDC researchers also found that older Americans had higher hospitalization and death rates, regardless of their vaccination status. People over age 65 have 80% protection instead of 95% against hospitalization and death.

Across all ages, Moderna's vaccine offered the highest protection against hospitalization at 95%, the study found. The Pfizer-BioNTech vaccine provided 80% protection and the Johnson & Johnson shot 60% protection.

Monitoring COVID-19 incidence by vaccination status might provide early signs that vaccine-related protection is waning, the researchers suggested.

Federal health officials continue to strongly encourage COVID-19 vaccinations for everyone ages 12 and older. Last week, President Joe Biden announced new executive orders mandating vaccinations for federal government employees and large businesses.

As of Monday, 75.7% of U.S. adults had received at least one dose of a COVID-19 vaccine, according to the CDC COVID Data Tracker.

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