More Evidence Pfizer Vax Mostly Holds Up Against Severe COVID

Effectiveness of Pfizer/BioNTech’s COVID vaccine (Comirnaty) waned against symptomatic disease at 5 months after vaccination, though was still highly effective at preventing hospitalization, real-world data from the U.K. found.

At 20 weeks or more following vaccination, Pfizer’s vaccine effectiveness was 66.3% (95% CI 65.7-66.9) against symptomatic COVID with Delta, but remained at 91.7% (95% CI 90.2-93.0) against hospitalization and 91.9% (95% CI 88.5-94.3) against death, reported Jamie Lopez Bernal, PhD, of the U.K. Health Security Agency in London, and colleagues.

While vaccine effectiveness dropped to 54.9% (95% CI 51.1-58.5) against symptomatic COVID among adults ages 65 and up, it remained at 90.5% (95% CI 87.6-92.7) against hospitalization, they wrote in the New England Journal of Medicine.

Not surprisingly, Pfizer’s vaccine was slightly less effective against Delta-related hospitalization at 20 weeks or more among adults ages 65 and up who were classified as “extremely clinically vulnerable” (78.6%, 95% CI 66.6-86.2), the authors noted.

Bernal’s group cited prior research from other countries, including Israel, that reported “substantially reduced protection against infection with the [Delta] variant.”

“Nevertheless, the extent to which reduced vaccine effectiveness is a result of a new variant or waning immunity remains unclear,” they wrote.

Their test-negative study design examined data from Dec. 8, 2020 to Oct. 1, 2021. It determined vaccination status for symptomatic adults with laboratory confirmed COVID (cases) versus vaccination status in adults who had COVID symptoms but tested negative via PCR (controls). These data were linked to the Emergency Care Data Set, which included emergency department visits resulting in inpatient admission among those with symptoms within 14 days after a positive test.

Overall, 6,056,673 PCR tests within 10 days of symptom onset were linked with vaccination status. Of those, 1,125,257 were infected with the Delta variant. There were 22,575 participants who were hospitalized within 14 days of testing positive, and 6,336 of those died within 28 days.

While Bernal’s group found that waning vaccine effectiveness was greater in adults ages 65 and up versus those ages 40-64, there was insufficient follow-up to estimate waning effectiveness in individuals ages 16-39, they said.

Protection against hospitalization with Delta was still extremely high among clinically vulnerable adults 40-64 at 20 weeks after vaccination (93.1%, 95% CI 94.3-96.9), they noted.

Limitations to the data include its observational nature, potential for bias, and that the study estimated vaccine effectiveness for those who sought testing, and may not be generalizable to the whole population. The authors did report similar evidence of waning of protection against symptomatic infection after the receipt of two doses of the Oxford/AstraZeneca vaccine, which currently is not FDA approved or authorized for use in the U.S.

“Our findings and those from Qatar and the United States raise important questions about the timing of third doses of vaccine in adults who remain protected against hospitalization and death for at least 5 months after the receipt of two doses,” Bernal’s group wrote. “The duration of protection offered by the third dose, however, is uncertain.”