VaccinesCOVID Vaccine Protection Waning Against Infection -- but Not Hospitalization

By Mary Van Beusekom

A trio of new real-world US studies examine the ongoing effectiveness of two doses of the Pfizer/BioNTech and Moderna mRNA vaccines against COVID-19, one finding significantly ebbing efficacy against infection in nursing home residents and two showing sustained protection against coronavirus-related hospitalizations but declining coverage against new adult cases.

The studies were cited Wednesday as White House officials announced plans to offer booster doses of the vaccines beginning next month (see related CIDRAP News story). They were published Wednesday in Morbidity and Mortality Weekly Report, the journal of the Centers for Disease Control and Prevention (CDC).

The results, the study authors said, underscore the need for heightened vigilance and a multipronged approach to prevent COVID-19 amid diminishing vaccine effectiveness (VE) and the ongoing surge of cases caused by the Delta (B1617.2) variant.

Nursing Home Protection Drops to 53.1%
In the first study, the researchers compared weekly reports of new infections by vaccination status from nursing homes certified by the Centers for Medicare & Medicaid Services to evaluate the VE of two doses of either mRNA vaccine before the emergence of Delta (Mar 1 to May 9, 2021) and after (Jun 21 to Aug 1).

Of all nursing home residents, 14.7% were unvaccinated, 49.6% were fully vaccinated with Pfizer, 25.3% were vaccinated with Moderna, and 10.4% had “other” vaccination status.

Before Delta predominated, data from 17,407 reports from 3,862 nursing homes showed that adjusted VE was 74.7%. But after, it fell to 53.1%, according to 85,593 reports from 14,917 facilities.

Pre-Delta, adjusted VE against infection among those fully vaccinated (vs unvaccinated) was 74.7% for either mRNA vaccine, 74.2% for Pfizer, and 74.7% for Moderna. After the emergence of Delta, adjusted VE against infection among fully vaccinated residents was 53.1% for either vaccine, 52.4% for Pfizer, and 50.6% for Moderna.

A total of 6,879 COVID-19 asymptomatic and symptomatic infections were identified, 30.7% of them in unvaccinated residents, 37.8% in those fully vaccinated with Pfizer, 18.9% in those fully vaccinated with Moderna, and 12.5% in residents with other vaccination status.

The researchers, who pointed out that their study couldn’t differentiate between the effects of Delta and falling vaccine-generated immunity, called for research into whether VE against severe disease in nursing home residents is also waning over time. Because they are typically older and frail, nursing home residents may have a less robust immune response to vaccines and are at high risk for poor COVID-19 outcomes, they added.