Three new studies report on COVID-19 vaccine effectiveness (VE) and antibody responses to Omicron, with one from Sweden finding a drop in two-dose VE against severe disease after the transition from the BA.1 to the BA.2 subvariant but three-dose protection remaining above 80% against severe disease.Also, a study from Hong Kong shows good antibody response against BA.2 after three doses, and one from the United States finds that nursing home patients who received a third dose had a 47% lower risk of Omicron infection.Three-dose vaccine efficacy above 80%A team led by a Skane University Hospital researcher conducted a vaccine-registry COVID-19 surveillance study of all 1,384,531 residents of a county in southern Sweden from Dec 27, 2020, when the COVID-19 vaccine rollout began in that country, to Mar 15, 2022.
The findings were published yesterday in Eurosurveillance.Most doses (77%) were of the Pfizer/BioNTech COVID-19 vaccine, with Moderna and AstraZeneca/Oxford making up the remaining doses.The study spanned three periods: week 52 of 2021 to week 1 of 2022, in which Omicron BA.1 was dominant (60% vs 25% Delta and 15% BA.2); weeks 2 and 3 of 2022, the transition period (BA.1 [47%], Delta [4.5%], and BA.2 [49%]); and weeks 4 to 11 of 2022, when BA.2 was dominant (82% vs 17% BA.1 and 0.5% Delta).A total of 593 severe COVID-19 infections occurred, corresponding to 65, 78, and 56 cases each week during BA.1 dominance, the transition period, and BA.2, respectively.
Relative to the BA.1 period, during the BA.2 period, patients with severe illness were older and had a more even sex distribution.
The overrepresentation of patients born outside of Sweden during BA.1 lessened during BA.2, but these patients had a similar