New report shows high, continued vaccine effectiveness against severe COVID-19

A new Morbidity and Mortality Weekly Report shows little change in incidence rate ratios for hospitalization and death from severe COVID-19 after the SARS-CoV-2 delta variant reached predominance in 13 U.S. jurisdictions.

From April 4 to July 17, among adults who were not fully vaccinated, there were 569,142 COVID-19 cases (92%), 34,972 COVID-19 hospitalizations (92%) and 6,132 COVID-19-associated deaths (91%). In fully vaccinated adults, there were 46,312 COVID-19 cases (8%), 2,976 COVID-19 hospitalizations (8%) and 616 COVID-19-associated deaths (9%).

When the researchers analyzed the earlier period of April 4 to June 19, 5% of COVID-19 cases, 7% of COVID-19 hospitalizations and 8% of COVID-19-associated deaths were reported in fully vaccinated adults. These percentages increased in from June 20 to July 17 to 18%, 14% and 16%, respectively.

From April 4 to July 17, the weekly prevalence of the SARS-CoV-2 delta variant increased from less than 1% to 90%.

Full COVID-19 vaccination coverage also increased during this period, from 19% to 54%. From July 10 to 17, the range of full vaccination coverage was 45% among adults aged 18 to 49 years to 73% among adults aged 65 years and older.

“After the week of June 20, 2021, when the SARS-CoV-2 delta variant became predominant, the percentage of fully vaccinated persons among cases increased more than expected for the given vaccination coverage and a constant vaccine effectiveness,” Heather M. Scobie, PhD, from the Epidemiology Task Force for the CDC COVID-19 Response Team, and colleagues wrote in MMWR Weekly Report.

Average weekly age-standardized incidence rate ratios (IRRs) were higher among non-fully vaccinated adults than fully vaccinated adults from April 4 to June 19, including reported cases (112.3 vs. 10.1 per 100,000 persons), hospitalizations (9.1 vs. 0.7 per 100,000 persons) and deaths (1.6 vs. 0.1 per 100,000 persons), and also from June 20 to July 17 (89.1 vs. 19.4 per 100,000 persons, 7 vs. 0.7 per 100,000 persons and 1.1 vs. 0.1 per 100,000 persons, respectively). Age-standardized IRRs for cases in those who were not fully vaccinated compared with those who were fully vaccinated decreased from 11.1 to 4.6 from April 4 to June 19 vs. June 20 to July 17; IRRs for hospitalizations (decline from 13.3 to 10.4) and deaths (decline from 16.6 to 11.3) also decreased between these two periods.

“Findings were consistent with a potential decline in vaccine protection against confirmed SARS-CoV-2 infection and continued strong protection against COVID-19-associated hospitalization and death,” Scobie and colleagues wrote.

The 13 U.S. jurisdictions were Alabama, Arizona, Colorado, Indiana, Los Angeles County (California), Louisiana, Maryland, Minnesota, New Mexico, New York City (New York), North Carolina, Seattle/King County (Washington) and Utah.