Dataset Information

Vaccine effectiveness against Delta, Omicron BA.1 and BA.2 in a highly vaccinated Asian setting: a test-negative design study

ABSTRACT:

Objectives

We compared the vaccine effectiveness over time of the primary series and booster against infection and severe disease with Delta, Omicron BA.1 and BA.2 variants in Singapore, an Asian setting with high vaccination coverage.

Methods

We conducted a test-negative case-control study on all adult Singapore residents who received COVID-19 PCR testing in acute hospitals. Individuals with negative PCR from 1 September 2021 to 30 November 2021 and 1 December 2021 to 25 April 2022 served as controls for Delta and Omicron variants respectively, while PCR-positive individuals within these two time periods served as cases. Association between vaccination status and SARS-CoV-2 infection and severe disease with Delta or Omicron variants were measured with Poisson regressions. Vaccine effectiveness was calculated by taking 1 minus risk ratio.

Results

There were 68,114 individuals comprising 58,495 controls and 9,619 cases for the Delta period, of whom 53,093 completed the primary series and 9,161 were boosted. For the Omicron period, 104,601 individuals comprising 80,428 controls, 8,643 BA.1 cases and 15,530 BA.2 cases were included, of whom 29,183 and 71,513 were vaccinated with the primary series and boosted respectively. The primary series provided greater protection against infection with Delta (45%, 95% CI 40–50%) compared with Omicron (21%, 95% CI 7–34% for BA.1; 18%, 95% CI 6–29% for BA.2) at <2 months from vaccination. Vaccine effectiveness of the booster against infection with BA.1 (44%, 95% CI 38–50%) and BA.2 (40%, 95% CI 35–40%) was similar. Protection against severe disease by the booster for BA.1 (83%, 95% CI 76–88%) and BA.2 (78%, 95% CI 73–82%) is comparable to that by the primary series for Delta (80%, 95% CI 73–85%).

Conclusion

Our findings support the use of a booster dose to reduce the risk of severe disease and mitigate the impact on the healthcare system in an Omicron-predominant epidemic.

SUBMITTER: Tan C

PROVIDER: S-EPMC9398552 | biostudies-literature | 2022 Aug

REPOSITORIES: biostudies-literature

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Project description:ImportanceStudies have reported increased risk of autoimmune sequelae after SARS-CoV-2 infection. However, risk may potentially be attenuated by milder Omicron (B.1.1.529) variant infection and availability of booster vaccination.ObjectiveTo estimate the 300-day risk of new-incident autoimmune sequelae after SARS-CoV-2 Delta or Omicron BA.1 or BA.2 variant infection in adults who received COVID-19 vaccines and boosters, compared with a contemporary control group without infection.Design, setting, and participantsThis cohort study in Singapore enrolled adults from September 1, 2021, to March 7, 2022, and followed up for 300 days. Participants were adults aged 18 years or older with SARS-CoV-2 infection during the predominance of the Delta and Omicron BA.1 or BA.2 variants and were still alive at 30 days after COVID-19 diagnosis.ExposureThe national SARS-CoV-2 testing registry was used to construct cohorts of adults with SARS-CoV-2 Delta or Omicron BA.1 or BA.2 variant infection (hereafter, cases) and a contemporaneous group with negative polymerase chain reaction or rapid antigen test results (hereafter, controls).Main outcomes and measuresNew-incident autoimmune diagnoses after SARS-CoV-2 infection. This information was recorded in the MediClaims national health care claims database and identified 31 to 300 days after index date of infection. Risks and excess burdens were estimated using Cox proportional hazards regression model with overlap weights applied.ResultsIn total, 1 766 036 adults (915 096 females [51.9%]; mean [SD] age, 49 [18] years) were included in the study population, with 480 082 (27.2%) categorized as cases and 1 285 954 (72.8%) as controls. Of these adults, 73.1% had Chinese, 13.7% Malay, and 9.9% Indian ethnicity. There were 104 179 cases and 666 575 controls included during the Delta variant-predominance transmission, while 375 903 cases and 619 379 controls were included during the Omicron variant-predominance transmission. During the Delta variant period, 81.1% of cases had completed primary vaccination; during the Omicron variant period, 74.6% of cases received boosters. No significantly elevated risk of 12 prespecified autoimmune sequelae was recorded across the Omicron and Delta variant cohorts. Elevated risks of inflammatory bowel disease (adjusted hazard ratio [AHR], 2.23; 95% CI, 1.45-3.46; P < .001) and bullous skin disorders (AHR, 4.88; 95% CI, 2.47-9.66; P < .001) were observed only in the subset of COVID-19 cases requiring hospitalization during the predominance of the Omicron variant. While elevated risk of vasculitis (AHR, 5.74; 95% CI, 1.48-22.23; P = .01) was observed in vaccine-breakthrough Omicron variant infections, no increased risk of vasculitis was observed in the corresponding subgroup who received boosters.Conclusions and relevanceThis cohort study observed no significantly elevated long-term risk of autoimmune sequelae after SARS-CoV-2 Delta and Omicron BA.1 or BA.2 variant infection, except for a modestly increased risk of inflammatory bowel disease and bullous skin disorders in the hospitalized subgroup during the predominance of the Omicron variant. Booster vaccination appeared to mitigate the risk of long-term autoimmune sequelae.