Results of Earlier An infection and Vaccination on Symptomatic Omicron Infections


Research Inhabitants and Information Sources

The research was performed within the resident inhabitants of Qatar. We analyzed info from the nationwide, federated databases concerning Covid-19 vaccination, laboratory testing, hospitalization, and loss of life. These information had been retrieved from the built-in nationwide digital-health info platform. The databases included all SARS-CoV-2–associated information and related demographic info for the reason that begin of the pandemic. These databases embody, with no lacking info, outcomes of all polymerase-chain-reaction (PCR) testing and, extra not too long ago, fast antigen testing performed at well being care services on or after January 5, 2022.

All PCR testing (however not fast antigen testing) carried out in Qatar is assessed on the idea of signs and the explanation for testing. Of all of the PCR checks performed throughout this research, 19.2% had been carried out due to scientific signs. Qatar has an unusually younger, various inhabitants — solely 9% of its residents are 50 years of age or older, and 89% are expatriates from greater than 150 international locations.10 Qatar launched its Covid-19 vaccination program in December 2020 with the BNT162b2 and mRNA-1273 vaccines.11 Additional descriptions of the research inhabitants and the nationwide databases have been reported beforehand.4,10-15

Research Design

The research assessed the effectiveness of earlier an infection, vaccination with BNT162b2 or mRNA-1273, and hybrid immunity (earlier an infection and vaccination) in opposition to symptomatic an infection with BA.1, BA.2, and any omicron an infection.2,15-18 We used a test-negative, case–management design, by which effectiveness estimates had been derived by evaluating the chances of earlier an infection or vaccination or each amongst case members (individuals with a constructive PCR take a look at) with that amongst controls (PCR-negative individuals).2,15-18 We additionally assessed effectiveness in opposition to any extreme, important, or deadly case of Covid-19.

To estimate the effectiveness in opposition to symptomatic an infection, we precisely matched circumstances and controls that had been recognized from December 23, 2021, by February 21, 2022. Case members and controls had been matched in a 1:1 ratio based on intercourse, 10-year age group, nationality, and calendar week of PCR take a look at. Matching was carried out to manage for identified variations within the threat of SARS-CoV-2 publicity in Qatar.10,19,20 Matching based on these elements was beforehand proven to supply enough management of variations within the threat of SARS-CoV-2 publicity in research of various designs, all of which concerned management teams, comparable to test-negative, case–management research.11,12,15,21,22 To evaluate effectiveness in opposition to any extreme, important, or deadly case of Covid-19, we used a 1:5 matching ratio to enhance the statistical precision of the estimates.

Solely the primary PCR-positive take a look at that was recognized for a person participant throughout the research interval was included, however all PCR-negative checks had been included. Controls included individuals with no document of a PCR-positive take a look at throughout the research interval. Solely PCR checks performed due to scientific signs had been used within the analyses.

SARS-CoV-2 reinfection is conventionally outlined as a documented an infection that happens no less than 90 days after an earlier an infection, to keep away from misclassification of extended PCR positivity as reinfection if a shorter time interval is used.2,23 Earlier an infection was due to this fact outlined as a PCR-positive take a look at that occurred no less than 90 days earlier than the PCR take a look at used within the research. Checks for individuals who had PCR-positive checks that occurred inside 90 days earlier than the PCR take a look at used within the research had been excluded. Accordingly, earlier infections on this research had been thought-about to be because of variants aside from omicron, since they occurred earlier than the omicron wave in Qatar.2-4

PCR checks for individuals who obtained vaccines aside from BNT162b2 or mRNA-1273 and checks for individuals who obtained blended vaccines had been excluded from the analyses. Checks that occurred inside 14 days after a second dose or 7 days after a 3rd dose of vaccine had been excluded. These inclusion and exclusion standards had been applied to permit for build-up of immunity after vaccination4,14 and to attenuate various kinds of potential bias, as knowledgeable by earlier analyses in the identical inhabitants.12,22 Each management that met the inclusion standards and that might be matched to a case was included within the analyses.

We in contrast 5 teams with the group that had no earlier an infection and no vaccination. The 5 teams had been characterised by kind of publicity: earlier an infection and no vaccination, two-dose vaccination and no earlier an infection, two-dose vaccination and former an infection, three-dose vaccination and no earlier an infection, and three-dose vaccination and former an infection. The teams had been outlined on the idea of the standing of earlier immunologic occasions (earlier an infection or vaccination) on the time of the PCR take a look at.

Classification of extreme,8 important,8 and deadly9 Covid-19 circumstances adopted World Well being Group pointers, and assessments had been made by skilled medical personnel with the usage of particular person chart critiques as a part of a nationwide protocol utilized to hospitalized sufferers with Covid-19. Particulars concerning Covid-19 severity, criticality, and fatality classification are supplied in Part S1 within the Supplementary Appendix.

Laboratory Strategies and Subvariant Ascertainment

The massive omicron wave in Qatar began on December 19, 2021, and peaked in mid-January 2022.2-4 A complete of 315 random SARS-CoV-2–constructive specimens collected from December 19, 2021, by January 22, 2022, underwent viral whole-genome sequencing on a GridION sequencing gadget (Nanopore Applied sciences). Of those specimens, 300 (95.2%) had been confirmed to be omicron infections and 15 (4.8%) to be delta (or B.1.617.2)1 infections.2-4 Of the 286 omicron infections with confirmed subvariant standing, 68 (23.8%) had been BA.1 and 218 (76.2%) had been BA.2.

We used the TaqPath COVID-19 Combo Equipment (Thermo Fisher Scientific), which checks for the spike (S) gene of SARS-CoV-2 and the 69-70del mutation within the S gene,24 to determine BA.1 and BA.2 infections. An S-gene goal failure was used as a proxy for BA.1 an infection, and a non–S-gene goal failure was used as a proxy for BA.2 an infection. Extra particulars concerning laboratory strategies for real-time reverse-transcriptase–quantitative PCR testing are supplied in Part S2.


This retrospective research was authorised by the institutional overview boards at Hamad Medical Company and Weill Cornell Medication–Qatar, with a waiver of knowledgeable consent. The reporting of this research follows the Strengthening the Reporting of Observational Research in Epidemiology pointers (Desk S1). The funders of the research had no function in research design, information assortment, information evaluation, information interpretation, or writing of the manuscript. All of the authors contributed to information assortment and acquisition, dialogue and interpretation of the outcomes, and the writing of the manuscript. All of the authors learn and authorised the ultimate manuscript.

Statistical Evaluation

Though all data of PCR testing had been examined for choice of circumstances and controls, solely matched samples had been analyzed. Instances and controls had been described with the usage of frequency distributions and measures of central tendency and in contrast with the usage of standardized imply variations. The standardized imply distinction was outlined because the distinction between the imply worth of a covariate in a single group and the corresponding imply worth of a covariate within the different group, divided by the pooled normal deviation, with values of lower than 0.1 indicating enough matching.25

Odds ratios, which in contrast the chances of earlier an infection or vaccination or each amongst circumstances with that amongst controls, and related 95% confidence intervals had been derived with the usage of conditional logistic regression. This analytic method, which additionally integrated matching based on calendar week of PCR take a look at, minimizes potential bias because of variation in epidemic part16,26 and roll-out of vaccination throughout the research interval.16,26 Confidence intervals weren’t adjusted for multiplicity and due to this fact shouldn’t be used to deduce definitive variations amongst publicity teams. Interactions weren’t investigated. Effectiveness and related 95% confidence intervals had been calculated as 1 minus the chances ratio of earlier an infection or vaccination or each amongst circumstances as in contrast with controls.16,17 The reference group for all estimates included individuals with no earlier an infection and no vaccination.

An extra evaluation was performed to analyze the consequences of earlier an infection, two-dose vaccination, and three-dose vaccination as a perform of time for the reason that immunologic occasion (earlier an infection or vaccination). This evaluation used the identical method as the first evaluation, however with stratification based on time since the newest immunologic occasion.

An individual was thought-about to have had a earlier constructive take a look at if that take a look at was constructive by PCR assay. A sensitivity evaluation of effectiveness in opposition to any symptomatic omicron an infection was performed, however with earlier constructive testing being primarily based on constructive PCR in addition to constructive fast antigen checks, to analyze whether or not exclusion of fast antigen–constructive checks might have biased our estimates. Statistical analyses had been carried out with the usage of Stata/SE software program, model 17.0 (StataCorp).


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