The same week that Pfizer’s COVID-19 vaccine received full approval from the U.S. Food and Drug Administration, the Centers for Disease Control and Prevention published a new study offering additional strong, real-world data on how well vaccination actually protects people against infection, hospitalization, and death due to the coronavirus. The results confirm that vaccinated people have much greater protection against the virus—and against the need for hospitalization especially—compared with unvaccinated people.
For the study, published on August 24 in the CDC’s Morbidity and Mortality Weekly Report, researchers from the Los Angeles County Department of Public Health analyzed data on the 43,127 people (aged 16 and over) living in Los Angeles County who were diagnosed with confirmed cases of COVID-19 between May 1 and July 25, 2021.
During this three-month period, a few key dynamics of the virus shifted in the local area. First, vaccinations increased significantly, with the full vaccination rate for L.A. residents rising from 27% on May 1 to 51% on July 25. Meanwhile, infection rates and hospitalization rates also rose substantially, most noticeably among unvaccinated people. That’s largely due to the rise of the highly transmissible delta variant, which became the predominant strain during this time.
Throughout the study period, a significant majority of infections (71.4%) occurred in unvaccinated people, while 25.3% of cases occurred in fully vaccinated people. (Another 3.3% occurred in partially vaccinated people.) At the end of the study, on July 25, rates of infection were 4.9 times higher in unvaccinated people than in vaccinated people. And unvaccinated people were a whopping 29.2 times more likely to be hospitalized than fully vaccinated people.
Of the fully vaccinated people diagnosed with COVID-19, just 3.2% were hospitalized (350 people out of 10,895 cases), compared with 7.6% of unvaccinated people (2,355 people out of 30,801 cases). Those who were fully vaccinated were also less likely to need intensive treatment after being admitted to the hospital: While 0.5% were admitted to the ICU and 0.2% needed mechanical ventilation, those rates jumped to 1.5% and 0.5%, respectively, among unvaccinated patients with COVID-19.
Vaccination also significantly reduced the risk of dying due to COVID-19. Of the 207 COVID-19 deaths that occurred during the study period, 176 (85%) were among unvaccinated people. It’s also worth noting here that one-quarter of the 24 fully vaccinated people who died were immunocompromised (the group included people with an HIV infection, cancer, or a liver transplant). Evidence indicates that immunocompromised individuals get less protection from the COVID-19 vaccine because their bodies have a hard time mounting a sufficient immune system response (which is why the FDA authorized booster shots for immunocompromised people). Ultimately, the death rate was about three times higher in unvaccinated people than fully vaccinated people (0.6% vs. 0.2%, respectively).
This study also provides evidence that the protective effect of getting vaccinated is still strong against the delta variant, given that delta became the most common strain in L.A. during the time period examined. At the start, delta accounted for only about 8% of cases. But the prevalence of delta jumped to about 90% by the end.
Overall, this study adds to the pile of evidence that getting vaccinated seriously reduces a person’s risk for infection, hospitalization, and death from COVID-19—and drives home the point that widespread vaccination is our way out of the pandemic.
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