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).

Read more...