NEW YORK (Reuters Health) – Prior to the emergence of Omicron, both people previously infected with the novel coronavirus and those vaccinated against it were at much lower risk of catching COVID-19 than peers without prior COVID-19 who remained unvaccinated, a study from the Cleveland Clinic in Ohio shows.
With the emergence of Omicron, however, early findings suggest a substantial increase in risk of infection for all individuals, including those previously infected and those vaccinated, Dr. Nabin Shrestha and colleagues report in Clinical Infectious Diseases.
The researchers assessed the need for COVID-19 vaccination among people with prior COVID-19 infection. They studied more than 52,000 adults working at the Cleveland Clinic in Ohio on December 16, 2020, the day COVID-19 vaccination started.
Among these, 4,718 (9%) had prior COVID-19 and 36,922 (71%) were fully vaccinated by the end of the study (December 27, 2021).
A total of 7,851 (15%) employees acquired COVID-19 during the study, of whom 4,675 (60%) were symptomatic infections and 133 (1.7%) required hospitalization for COVID-19.
Fewer employees previously infected were vaccinated by the end of the study compared with those not previously infected (63% vs. 71%; P<0.001).
According to the researchers, the cumulative incidence of COVID-19 was “substantially higher throughout for those previously uninfected who remained unvaccinated than for all other groups, lower for the vaccinated than unvaccinated, and lower for those previously infected than those not.”
After the Omicron variant emerged, cases of COVID-19 increased “dramatically” in all groups.
In multivariable analysis, both prior COVID-19 and vaccination were independently associated with significantly lower risk of COVID-19, they report.
Previously infected employees did not have a lower risk of COVID-19 overall but vaccination was associated with a significantly lower risk of symptomatic COVID-19 both before Omicron (hazard ratio, 0.60; 95% CI, 0.40 to 0.90) and after Omicron (HR, 0.36; 95% CI, 0.23 to 0.57).
The study demonstrates that both previous infection and vaccination provide “substantial protection” against COVID-19, Dr. Shrestha told Reuters Health by email.
“Individuals previously infected with COVID-19 are substantially protected against COVID-19 for several months. Beyond that time, vaccination protects against symptomatic COVID-19, possibly by boosting of waning natural immunity,” he added.
“The arrival of the Omicron variant greatly changed the risk of COVID-19 for all individuals regardless of whether they were previously infected or not, and regardless of whether they were previously vaccinated or not. Protection against COVID-19 from prior infection or vaccination may be of shorter duration than before the arrival of the Omicron variant,” Dr. Shrestha added.
“It’s important to note that the study was conducted in an active, healthcare employee population. It included no children, very few elderly individuals and likely few immunocompromised individuals,” he said.
SOURCE: https://bit.ly/32mAQ9a Clinical Infectious Diseases, online January 13, 2022.
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