CDC study finds unvaccinated people nearly 5 times more likely to get COVID-19

Aug. 26, 2021

People who are not vaccinated against COVID-19 are 4.9 times more likely to get COVID-19 and the 29.2 times more likely to be hospitalized than fully vaccinated people, the Centers for Disease Control and Prevention (CDC) reported in its Morbidity and Mortality Weekly Report (MMWR). That summary was based on data on SARS-CoV-2 infections from Los Angeles County on July 25, when the Delta variant was pervasive.

Among 43,127 reported SARS-CoV-2 infections in Los Angeles County residents at least 16 years of age, 10,895 (25.3%) were in fully vaccinated people, 1,431 (3.3%) were in partially vaccinated people, and 30,801 (71.4%) were in unvaccinated people.

Much lower percentages of fully vaccinated people infected with SARS-CoV-2 were hospitalized (3.2%), were admitted to an intensive care unit (0.5%), and required mechanical ventilation (0.2%), compared with partially vaccinated people (6.2%, 1.0%, and 0.3%, respectively), and unvaccinated people (7.6%, 1.5%, and 0.5%, respectively).

During May 1-July 25, the percentages of B.1.617.2 (Delta) variant infections estimated from 6,752 samples with lineage data increased among fully vaccinated persons (from 8.6% to 91.2%), partially vaccinated persons (from 0% to 88.1%), and unvaccinated persons (from 8.2% to 87.1%).

In May, there were differences in median Ct values by vaccination status; however, by July, no differences were detected among specimens from fully vaccinated, partially vaccinated, and unvaccinated people by gene targets, meaning that all of them carried a similar viral load.

To characterize post-vaccination infections in the report, the Los Angeles County Department of Public Health (LACDPH) used COVID-19 surveillance and California Immunization Registry 2 (CAIR2) data to describe age-adjusted infection and hospitalization rates during May 1-July 25, 2021, by vaccination status.

Whole genome sequencing (WGS)-based SARS-CoV-2 lineages and cycle threshold (Ct) values from qualitative reverse transcription-polymerase chain reaction (RT-PCR) for two SARS-CoV-2 gene targets, including the nucleocapsid (N) protein gene region and the open reading frame 1 ab (ORF1ab) polyprotein gene region, were reported for a sample of the specimens.

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