Vaccine effectiveness against SARS-CoV-2 infection with the Omicron or Delta variants following a two-dose or booster BNT162b2 or mRNA-1273 vaccination series: A Danish cohort study

Hansen, Christian Holm; Schelde, Astrid Blicher; Moustsen-Helms, Ida Rask; Emborg, Hanne‐Dorthe; Krause, Tyra Grove; Moelbak, Kaare; Valentiner‐Branth, Palle

doi:10.1101/2021.12.20.21267966

Cited by 134 publications

(149 citation statements)

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“…Our results align more closely with recent Danish data, where VE was estimated for both BNT162b2 and mRNA-1273 vaccines between November 20 and December 12, 2021. 12 In both Ontario and Denmark, VE was estimated against any infection; these estimates are expected to be lower than against symptomatic infection. In the Danish study, there was no significant protection against Omicron infection beyond 31 days after the second dose of BNT162b2, with significant negative VE estimates 91-150 days after the second dose.…”

Section: Discussionmentioning

confidence: 99%

“…Despite very high 2-dose COVID-19 vaccine coverage (88% among those aged ≥12 years by mid-December), 2 the rate of cases among fully vaccinated individuals increased substantially during this period. 3 While reduced neutralizing antibodies against Omicron following second and third doses of mRNA vaccines has been established, [4][5][6][7][8][9] real-world data evaluating vaccine performance against Omicron infection are more limited, [10][11][12] particularly in a North American context. The objective of this study was to estimate vaccine effectiveness (VE) against infection caused by Omicron or Delta in Ontario.…”

Section: Introductionmentioning

confidence: 99%

“…While reduced neutralizing antibodies against Omicron following second and third doses of mRNA vaccines has been established, 4-9 real-world data evaluating vaccine performance against Omicron infection are more limited, 10-12 particularly in a North American context. The objective of this study was to estimate vaccine effectiveness (VE) against infection caused by Omicron or Delta in Ontario.…”

Section: Introductionmentioning

confidence: 99%

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Effectiveness of COVID-19 vaccines against Omicron or Delta symptomatic infection and severe outcomes

Buchan

Chung

Brown

et al. 2022

Preprint

133

125

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Background The incidence of SARS-CoV-2 infection, including among those who have received 2 doses of COVID-19 vaccines, has increased substantially since Omicron was first identified in the province of Ontario, Canada. Methods Applying the test-negative design to linked provincial data, we estimated vaccine effectiveness against infection (irrespective of symptoms or severity) caused by Omicron or Delta between November 22 and December 19, 2021. We included individuals who had received at least 2 COVID-19 vaccine doses (with at least 1 mRNA vaccine dose for the primary series) and used multivariable logistic regression to estimate the effectiveness of two or three doses by time since the latest dose. Results We included 3,442 Omicron-positive cases, 9,201 Delta-positive cases, and 471,545 test-negative controls. After 2 doses of COVID-19 vaccine, vaccine effectiveness against Delta infection declined steadily over time but recovered to 93% (95%CI, 92-94%) ≥7 days after receiving an mRNA vaccine for the third dose. In contrast, receipt of 2 doses of COVID-19 vaccines was not protective against Omicron. Vaccine effectiveness against Omicron was 37% (95%CI, 19-50%) ≥7 days after receiving an mRNA vaccine for the third dose. Conclusions Two doses of COVID-19 vaccines are unlikely to protect against infection by Omicron. A third dose provides some protection in the immediate term, but substantially less than against Delta. Our results may be confounded by behaviours that we were unable to account for in our analyses. Further research is needed to examine protection against severe outcomes.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effectiveness of COVID-19 vaccines against Omicron or Delta symptomatic infection and severe outcomes

Buchan

Chung

Brown

et al. 2022

Preprint

133

125

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“…With over 30 mutations in the spike protein, a substantial ability to evade the neutralizing antibody response has been described [3][4][5][6] . This associates with greater capacity for reinfection 7 , as well as lower early estimates of vaccine effectiveness against symptomatic disease 8,9 . SARS-CoV-2-specific T cells play a key role in modulating COVID-19 severity [10][11][12] , and provide protective immunity in the context of suboptimal antibody titers 13 .…”

Section: Main Textmentioning

confidence: 99%

SARS-CoV-2 spike T cell responses induced upon vaccination or infection remain robust against Omicron

Keeton

Tincho

Ngomti

et al. 2021

Preprint

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The SARS-CoV-2 Omicron variant has multiple Spike (S) protein mutations that contribute to escape from the neutralizing antibody responses, and reducing vaccine protection from infection. The extent to which other components of the adaptive response such as T cells may still target Omicron and contribute to protection from severe outcomes is unknown. We assessed the ability of T cells to react with Omicron spike in participants who were vaccinated with Ad26.CoV2.S or BNT162b2, and in unvaccinated convalescent COVID-19 patients (n = 70). We found that 70-80% of the CD4 and CD8 T cell response to spike was maintained across study groups. Moreover, the magnitude of Omicron cross-reactive T cells was similar to that of the Beta and Delta variants, despite Omicron harbouring considerably more mutations. Additionally, in Omicron-infected hospitalized patients (n = 19), there were comparable T cell responses to ancestral spike, nucleocapsid and membrane proteins to those found in patients hospitalized in previous waves dominated by the ancestral, Beta or Delta variants (n = 49). These results demonstrate that despite Omicron's extensive mutations and reduced susceptibility to neutralizing antibodies, the majority of T cell response, induced by vaccination or natural infection, cross-recognises the variant. Well-preserved T cell immunity to Omicron is likely to contribute to protection from severe COVID-19, supporting early clinical observations from South Africa.

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“…Recent observational studies have suggested that vaccines for the omicron variant of SARS-Cov2 may have little or no effect in preventing infection while being effective in preventing hospitalisation. For example, a Danish study 1 found low vaccine efficacy against omicron infections: 55% for the BNT162b2 and 37% for the mRNA-1273 vaccine. However, for longer follow up (after 90 days) the "effectiveness" observed was negative (less than 0), triggering reports than vaccines paradoxically might increase omicron infections, which was picked up by multiple blogs and subsequently fact-checked by AP News 2 .…”

Section: Introductionmentioning

confidence: 99%

Testing behaviour may bias observational studies of vaccine effectiveness

Glasziou

McCaffery

Cvejic

et al. 2022

Preprint

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Background Recent observational studies have suggested that vaccines for the omicron variant of SARS-Cov2 may have little or no effect in preventing infection. However, the observed effects may be confounded by patient factors and preventive behaviours or vaccine-related differences in testing behaviour. To assess the potential degree of confounding, we aimed to estimate differences in testing behaviour between unvaccinated and vaccinated populations. Methods We recruited 1,526 Australian adults for an online randomised study about COVID testing between October and November 2021, and collected self-reported vaccination status and three measures of COVID-19 testing behaviour. We examined the association between testing intentions and vaccination status in the cross-sectional baseline data of this trial. Results Of the 1,526 participants (mean age 31 years): 22% had a COVID-19 test in the past month and 61% ever; 17% were unvaccinated, 11% were partially vaccinated (1 dose), 71% were fully vaccinated (2+ doses). Fully vaccinated participants were twice as likely to report positive COVID testing intentions than those who were unvaccinated (p<.001). Partially vaccinated participants had less positive intentions than those fully vaccinated (p<.001) but higher intentions than those who were unvaccinated (p=.002). Discussion For all three measures vaccination predicted greater COVID testing intentions. If the unvaccinated tested at half the rate of the vaccinated, a true vaccine effectiveness of 30% could appear to be a negative observed vaccine effectiveness of -40%. Assessing vaccine effectiveness should use methods to account for differential testing behaviours. Test negative designs are currently the preferred option, but its assumptions should be more thoroughly examined.

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Vaccine effectiveness against SARS-CoV-2 infection with the Omicron or Delta variants following a two-dose or booster BNT162b2 or mRNA-1273 vaccination series: A Danish cohort study

Cited by 134 publications

References 1 publication

Effectiveness of COVID-19 vaccines against Omicron or Delta symptomatic infection and severe outcomes

Effectiveness of COVID-19 vaccines against Omicron or Delta symptomatic infection and severe outcomes

SARS-CoV-2 spike T cell responses induced upon vaccination or infection remain robust against Omicron

Testing behaviour may bias observational studies of vaccine effectiveness

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