Study finds boosters give good protection against Omicron hospital casesA US study of almost 17,000 patients finds modest two-dose Pfizer COVID vaccine effectiveness (VE) against hospitalization and emergency department (ED) admission for Omicron BA.1 (the original Omicron variant) and the BA.2 subvariant, but three-dose VE was 79% and 71% for hospitalization, respectively, and 72% and 21% for ED visits.Also, VE 3 months or more after the third dose remained high except for BA.2 ED admission.The test-negative case-control study, by Kaiser Permanente and Pfizer scientists, was published in The Lancet Respiratory Medicine and involved 16,994 COVID-19 members of Kaiser Permanente Southern California—a US healthcare system—who were admitted for an acute respiratory infection.
Of those, 7,435 (43.8%) had BA.1, 1,056 (6.2%) had BA.2, and 8,503 (50.0%) did not have SARS-CoV-2.The researchers noted that two-dose Pfizer VE was 40% (95% confidence interval [CI], 27% to 50%) for hospitalization and 29% (95% CI, 18% to 38%) for ED admission against Omicron BA.1 and 56% (95% CI, 31% to 72%) for hospitalization and 16% (95% CI, –3% to 33%) for ED admission against BA.2.Three-dose VE was 79% (74% to 83%) for hospitalization and 72% (67% to 77%) for ED visit against BA.1 and 71% (55% to 81%) for hospitalization and 21% (1% to 37%) for ED visit against BA.2.
VE 3 months or more after the third dose was 76% (69% to 82%) against BA.1-related hospitalization and 65% (56% to 73%) against BA.1-related ED visit.
Against BA.2, VE 3 or more months after the third dose was 70% (53% to 81%) for hospitalization and 5% (−21% to 25%) for ED admission.In a related commentary, two infectious disease epidemiologists write, "Boosters restore vaccine