During period of delta predominance, protection was lower among vaccinated persons without previous COVID-19 diagnosis
MONDAY, Jan. 24, 2022 (HealthDay News) — Vaccination and previous COVID-19 infection were protective against COVID-19 infection and hospitalization during the alpha and delta severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) waves, according to research published in the Jan. 19 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.
Tom ¡s M. Le ³n, Ph.D., from the California Department of Public Health, and colleagues examined the impact of primary COVID-19 vaccination and previous SARS-CoV-2 infection on COVID-19 incidence and hospitalization rates by analyzing data from California and New York. Four cohorts of adults were considered: unvaccinated with no previous COVID-19 diagnosis; vaccinated with no previous COVID-19 diagnosis; unvaccinated with a previous COVID-19 diagnosis; and vaccinated with a previous COVID-19 diagnosis.
The researchers found that in both states, COVID-19 incidence was highest among unvaccinated individuals without a previous COVID-19 diagnosis compared with the other three groups. During the week beginning May 30, 2021, in California and New York, COVID-19 case rates were 19.9-fold and 18.4-fold lower, respectively, among vaccinated persons without a previous diagnosis; 7.2-fold and 9.9-fold lower, respectively, among unvaccinated persons with a previous COVID-19 diagnosis; and 9.6-fold and 8.5-fold lower, respectively, among vaccinated persons with a previous COVID-19 diagnosis compared with unvaccinated persons without a previous COVID-19 diagnosis. Hospitalization rates in California followed a similar pattern. In late June and July, these relationships changed after the SARS-CoV-2 delta variant became predominant. By the week beginning Oct. 3, 2021, the corresponding case rates were 6.2-fold and 4.5-fold lower among vaccinated persons without previous COVID-19 diagnosis, 29.0-fold and 14.7-fold lower among unvaccinated persons with previous diagnosis, and 32.5-fold and 19.8-fold lower among vaccinated persons with a previous diagnosis compared with unvaccinated persons without a previous COVID-19 diagnosis.
“Vaccination protected against COVID-19 and related hospitalization, and surviving a previous infection protected against a reinfection and related hospitalization during periods of predominantly alpha and delta variant transmission, before the emergence of omicron,” the authors write.
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