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Efficacy of vaccination in opposition to SARS-CoV-2 Omicron BA.1 and BA.2 sublineages in Sweden

In a latest examine posted to the medRxiv* preprint server, researchers in contrast the vaccine effectiveness (VE) in opposition to infections by extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant of concern (VOC) Omicron BA.1 and BA.2 sublineages in Sweden.

Study: COVID-19 vaccine effectiveness against severe disease from the Omicron BA.1 and BA.2 subvariants – surveillance results from southern Sweden, December 2021 to March 2022. Image Credit: Tong_stocker/Shutterstock
Research: COVID-19 vaccine effectiveness in opposition to extreme illness from the Omicron BA.1 and BA.2 subvariants – surveillance outcomes from southern Sweden, December 2021 to March 2022. Picture Credit score: Tong_stocker/Shutterstock

Research have reported that the Omicron BA.2 sublineage is extra transmissible than BA.1, with decrease safety conferred by vaccines in opposition to BA.2-associated hospitalizations and deaths. Nevertheless, some research have reported equal safety for each sublineages. Due to this fact, strong proof on the comparative VE in opposition to BA.1 and BA.2 sublineages is missing.

In regards to the examine

Within the current cohort examine, researchers in contrast VE in opposition to extreme coronavirus illness 2019 (COVID-19) brought on by BA.1 and BA.2 sublineages of the Omicron VOC between December 27, 2021, and March 15, 2022, amongst Scania County residents of southern Sweden. The people had been longitudinally adopted up for optimistic COVID-19 reviews, and hospitalizations, and had been assessed for COVID-19 severity.

Information for all residents of Scania had been obtained from routine pattern sequencing of COVID-19 circumstances for comparative VE evaluation throughout three durations: (i) BA.1 predominance (60%) in week 52, 2021 and week 1, 2022, (ii) transitional interval throughout week 2 and three, 2022 (BA.1 47%, BA.2 49%), and (iii) Omicron BA.2 predominance (82%), weeks 4 to 11 of 2022.

Information on all of the residents had been obtained from regional and nationwide registries by linking the private identification variety of the residents. Updates had been obtained weekly on the vaccination sort, date, and doses offered by the nationwide vaccination register.

Information on extreme COVID-19 sufferers had been offered by the SMINet, an digital system of Sweden’s public well being company. As well as, regional registers of well being had been used as sources of complementary information to quickly present COVID-19 exams information and to judge the impression of comorbidities on COVID-19 outcomes. The comorbid situations assessed included diabetes, weight problems, and problems of renal, hepatic, pulmonary, neurological methods, most cancers, immunosuppressive situations, and genetic ailments similar to Down’s Syndrome, thalassemia, and sickle cell anemia.

Extreme COVID-19 circumstances had been these with a minimal of one-day hospitalization 5 days earlier than and as much as two weeks after optimistic COVID-19 reviews with oxygen supplementation necessities of ≥ 5 L/minute or intensive care unit (ICU) admissions.

The continual density case-control sampling approach was used for matching the case and controls for age and intercourse and making information changes for variations in comorbidities and COVID-19 historical past. Logistic regression modeling and 95% confidence intervals (CI) had been used to check VE for extreme SARS-CoV-2 infections.

For each extreme COVID-19 case, 10 people with SARS-CoV-2-negative reviews obtained 90 days earlier than or in the identical timeframe as that of SARS-CoV-2-positive circumstances had been randomly chosen as controls. Solely vaccinations administered per week earlier than the date of COVID-19 prognosis had been chosen for the analyses.


Over 590 extreme COVID-19 circumstances had been detected in the course of the follow-up assessments, that corresponded to weekly 65 BA.1 predominant circumstances, 78 BA.1 to BA.2 transition circumstances, and 56 BA.2 circumstances. Though most (83%) of the examine members had been vaccinated, solely 57% booster vaccine uptake was noticed. Most (77%) of the examine members had been vaccinated with the BNT16b2 messenger ribonucleic acid (mRNA) vaccine. The extreme BA.2 circumstances had been extra prevalent within the aged with a extra uniform prevalence amongst each the sexes in comparison with BA.1 circumstances.

Earlier than follow-up, VE in opposition to extreme SARS-CoV-2 infections was excessive (imply VE 89%) between March and November 2021) and was steady throughout BA.1 predominance in December 2021.  Nevertheless, after two doses, VE declined remarkably from 90% (95% CI 78% to 95%) throughout BA.1 predominance to 54% (95% CI 13% to 75%) throughout BA.2 predominance. As well as, vaccine safety from prior COVID-19 historical past was additionally decrease after the transition to BA.2. This decline in VE was constant throughout all ages, comorbidities, and sexes. In distinction, amongst members who acquired three vaccine doses, the VE remained steady after the transition from BA.1 to BA.2.

To summarize, the examine findings highlighted the significance of booster vaccination to mitigate COVID-19 and that the immune-evasive Omicron BA.2 sublineage was extra prone to trigger extreme SARS-CoV-2 infections in comparison with the BA.1 sublineage. Nevertheless, additional research for continued monitoring of VE in opposition to BA.2 are required.

Research limitations

Information on the causative viral variants for each case for each interval had been missing. Thus, the true modifications in VE in the course of the transition from BA.1 to BA.2 may have been underestimated. As well as, the safety from the historical past of Omicron infections couldn’t be evaluated because the interval of follow-up with Omicron predominance is brief.

Additional, since routine testing is just not really useful any longer, VE in opposition to infections couldn’t be completely investigated. Moreover, the examine outcomes had excessive statistical uncertainty, indicated by broad CIs among the many subgroups.

*Vital discover

medRxiv publishes preliminary scientific reviews that aren’t peer-reviewed and, subsequently, shouldn’t be thought to be conclusive, information scientific apply/health-related habits, or handled as established info.


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