Effects of previous infection and vaccination on symptomatic Omicron infections

Population and data research

The study was conducted among the permanent population of Qatar. We obtain information from national and federal databases related to Covid-19 vaccination, laboratory testing, hospitalization, and mortality. These data were obtained from an integrated national digital health information platform. The databases contained all data related to SARS-CoV-2 and demographic information since the beginning of the pandemic. These databases include the results of all polymerase chain reaction (PCR) tests, which are not available at all, and recent rapid antigen tests performed in medical facilities on or before January 5, 2022.

All conventional PCR tests (but not the express antigen test) are classified based on symptoms and the cause of the test. 19.2% of all PCR tests performed during this study were performed due to clinical symptoms. Qatar has a particularly young and diverse population – only 9% of its population is over the age of 50 and 89% are migrants from more than 150 countries.10 Qatar began its Covid-19 vaccination program in December 2020 with the BNT162b2 and mRNA-1273 vaccines.11 Additional descriptions of the study population and national databases have been reported previously.4.10-15

Learning design

The study evaluated the effectiveness of previous infection, vaccination with BNT162b2 or mRNA-1273, and hybrid immunity (previous infection and vaccination) against symptomatic infection with BA.1, BA.2 and various omicron infections.2.15-18 We used a test-negative, case-control design, in which the effectiveness was assessed by comparing the participants in the process (those with a positive PCR test) with those who controlled the likelihood of a previous infection or vaccination, or both (PCR-negative people). .2.15-18 We also evaluated the efficacy of Covid-19 against severe, critical, or fatal cases.

To assess the effectiveness against symptomatic infection, we accurately matched the cases and controls identified between 23 December 2021 and 21 February 2022. The participants and control elements were matched in a 1: 1 ratio, depending on gender and age. , nationality and calendar week of PCR test. A series of matches were performed to control known differences in the risk of SARS-CoV-2 infection.10,19,20 Conformity to these factors has been demonstrated in studies of various designs to ensure adequate control of SARS-CoV-2 exposure risk differences, all of which involved control groups, such as test-negative, case-control studies.11,12,15,21,22 To evaluate the effectiveness of Covid-19 against any severe, severe, or fatal event, we used a 1: 5 correlation ratio to improve statistical accuracy of prices.

Only the first PCR-positive test identified for the individual participant during the study period was included, but all PCR-negative tests were included. The controls included people who did not have a PCR-positive test during the study period. Only PCR tests based on clinical symptoms were used in the analysis.

SARS-CoV-2 reinfection is conventionally defined as a documented infection that occurs at least 90 days after the previous infection, to avoid misclassification of long-lasting PCR positive as a disinfection if a shorter time interval is used.2.23 Therefore, the previous infection was identified as a PCR-positive test that took place at least 90 days before the PCR test used in the study. Tests for people with PCR-positive tests that were available 90 days prior to the PCR test used in the study were excluded. Therefore, in this study, previous infections were thought to be related to variants other than the omiron because they preceded the omicron wave in Qatar.2-4

PCR tests for people receiving vaccines other than BNT162b2 or mRNA-1273 and tests for people receiving mixed vaccines were excluded from the analysis. Tests were excluded within 14 days after the second dose or within 7 days after the third dose of the vaccine. These inclusion and exclusion criteria were implemented to strengthen immunity after vaccination4.14 and minimizing different types of potential adverse events, as reported in previous analyzes of the same population.12.22 Each control that met the inclusion criteria and matched the event was included in the analysis.

We compared five groups with previously uninfected and unvaccinated groups. Five groups were characterized by type of effect: no previous infection and no vaccination, two doses of vaccine and no previous infection, two doses of vaccine and previous infection, three doses of vaccine and no previous infection, three doses of vaccine and previous infection. The groups were identified based on previous immunological events (previous infection or vaccination) during the PCR test.

heavy classification,8 criticism,8 and leads to death9 Covid-19 cases were conducted in accordance with WHO guidelines and assessed by trained health workers by reviewing individual diagrams as part of a national protocol applicable to hospitalized patients with Covid-19. Detailed information on the severity, critical level, and mortality classification of Covid-19 is provided in Section S1 of the Appendix.

Laboratory methods and determination of subvariants

The largest omicron wave in the world began on December 19, 2021 and reached its peak in mid-January 2022.2-4 A total of 315 random SARS-CoV-2-positive samples collected between December 19, 2021 and January 22, 2022 performed sequencing of the entire virus genome in a GridION sequencing device (Nanopore Technologies). Of these samples, 300 (95.2%) were confirmed to be omicron infections and 15 (4.8%) were delta (or B.1.617.2).1 infections.2-4 Of the 286 confirmed microbial infections, 68 (23.8%) were BA.1 and 218 (76.2%) were BA.2.

We used the TaqPath COVID-19 Combo Kit (Thermo Fisher Scientific), which examines the SARS-CoV-2 spike (S) gene and the 69-70del mutation in the S gene.24 Detection of BA.1 and BA.2 infections. The S-gene target disorder was used as the proxy for BA.1 infection, and the non-S-gene target disorder was used as the proxy for BA.2 infection. Reverse transcriptase – Additional information on laboratory methods of quantitative PCR testing is provided in Section S2.


This retrospective study was approved by the Hamad Medical Corporation and the Weill Cornell Medicine-Qatar Institutional Review Board with no consent. The report of this study is in accordance with the guidelines for strengthening the report of observational studies in epidemiology (Table S1). Research sponsors played no role in research design, data collection, data analysis, data interpretation, or manuscript writing. All authors contributed to the collection and retrieval of data, the discussion and interpretation of the results, and the writing of the manuscript. All authors read and approved the final manuscript.

Statistical analysis

Although all PCR test records were checked to select cases and controls, only matching samples were analyzed. Cases and controls using frequency distribution and central trend measures were described and compared using standardized mean differences. The standardized mean difference was defined as the difference between the mean value of the covariance in one group and the corresponding mean value of the covariance in the other group divided by the standard deviation combined with values ​​less than 0.1 indicating adequacy. .25

Using conditional logistic regression, Odds coefficients and 95% confidence intervals were obtained that compared the probability of a previous infection or vaccination or both with controls. Introduced in accordance with the calendar week of the PCR test, this analytical method reduces the potential adverse effects due to variations in the epidemic phase.16.26 and vaccination during the study period.16.26 Reliability intervals are not plural, so they should not be used to make clear distinctions between impact groups. Relationships have not been studied. Efficacy and 95% confidence associated with it were calculated between 1 minus the probability ratio of previous infection or vaccination or two cases compared with controls.16.17 According to all estimates, the reference group included people who had no previous infection and had not been vaccinated.

Additional analysis was performed to investigate the effects of previous infection, two-dose vaccination, and three-dose vaccination as a function of the time following the immunological event (previous infection or vaccination). This assay used the same method as the main assay, but with stratification according to the time since the most recent immunological event.

If this test is positive by PCR, the person is considered to have passed the previous positive test. Susceptibility to efficacy against any symptomatic omycron infection was analyzed, but the previous positive test was based on positive PCR as well as positive rapid antigen tests to examine whether the removal of rapid antigen-positive tests could adversely affect our grades. Statistical analysis was performed using Stata / SE software, version 17.0 (StataCorp).

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