Vaccine effectiveness towards SARS-CoV-2 reinfection in periods with totally different dominant SARS-CoV-2 variants
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A brand new research posted on the medRxiv* preprint server discovered that regardless of a decrease coronavirus illness 2019 (COVID-19) vaccine efficacy towards reinfection with the Omicron variant, these vaccines show a marked efficacy towards reinfection with extreme acute respiratory coronavirus 2 (SARS-CoV-2) Alpha and Delta variants, in addition to the Omicron variant––lasting as much as 9 months, post-vaccination. Therefore, people who’ve been contaminated by the virus up to now should additionally receive COVID-19 vaccination.

Study: Vaccine effectiveness towards SARS-CoV-2 reinfection in periods of Alpha (B.1.1.7), Delta (B.1.617.2) or Omicron (B.1.1.529) dominance: A Danish nationwide research. Image Credit: Willyam Bradberry/Shutterstock


Observational research have investigated incidences of SARS-CoV-2 reinfection regardless of COVID-19 vaccination. However, information on the span of COVID-19 vaccine efficacy put up a SARS-CoV-2 an infection is missing.

Although reinfections with non-Omicron variants appear to be naturally restricted, decrease safety towards reinfection with the Omicron variant was documented in Denmark and Qatar.

The research

A brand new research aimed to look at the extra advantages of COVID-19 vaccination in people with a previous episode of SARS-CoV-2 an infection.

A COVID-19 vaccination drive was deployed in Denmark in accession, starting on the finish of December 2020. Thereafter, a booster vaccination marketing campaign was outlined equally from September 2021. The vaccines administered have been Comirnaty (BNT162b2), Vaxzevria (ChAdOx1), Spikevax (mRNA-1273), and Janssen (Ad26.COV2-S).

This nationwide, population-based cohort research additionally investigated the time because the mass vaccinations when the SARS-CoV-2 variants Alpha, Delta, or Omicron turned dominant.


Higher than 84% of the people included acquired Comirnaty and Spikevax messenger ribonucleic acid (mRNA) vaccines. While most people who accomplished the first vaccination collection through the Alpha interval have been of superior age, females, and had comorbidity. On the opposite hand, the vast majority of people who accomplished the first vaccination collection through the Alpha interval had the bottom median age.

The Alpha interval recorded 437 confirmed SARS-CoV-2 reinfections; the vaccine effectiveness (VE) elicited vital ranges 14-43 days after vaccination and to 85% about 104 days after vaccination. Reinfections have been documented in 1,678 people through the Delta wave; the adjusted VE was 88% post-vaccination (14-43 days after). The VE was statistically insignificant 284 days post-vaccination.

With the Omicron variant, though the VE peaked at 60% post-vaccination (14-43 days), it plummeted to 14% inside 164-193 days after vaccination. The VE was statistically insignificant after 284-313 days.

The outcomes indicated that the VE decreased with time, and this waning was extra fast for the Omicron variant when in comparison with the Delta variant. However, VE towards hospitalization and dying couldn’t be estimated.

The outcomes confirmed that main COVID-19 vaccination elicited vital efficacy for defense towards SARS-CoV-2 reinfection through the Alpha, Delta, and Omicron waves of the pandemic. Periods of Delta and Omicron dominance recorded the best short-term VEs – which have been decrease through the Omicron interval than within the Delta interval.

Meanwhile, the Alpha wave documented an initially low VE, which rose 104 days post-vaccination. This was possible as a result of slower immune response generated by the populations that acquired vaccinations throughout this era – who have been older and/or immunocompromised.

Additionally, one other research from the United States revealed that hospitalized sufferers who acquired two doses of COVID-19 mRNA vaccines had a decrease VE through the Omicron interval than these within the Delta interval.


The findings confirmed that vaccinated people who have been beforehand contaminated stay protected towards SARS-CoV-2 reinfections from Alpha, Delta, and Omicron variants as much as 9 months after the completion of the first vaccination collection. However, the diploma of safety towards the omicron variant is subdued. The outcomes are of relevance to public well being and ensure that beforehand contaminated people additionally profit from COVID-19 vaccinations as these vaccines present immunity to all three SARS-CoV-2 variants of concern.

*Important discover

medRxiv publishes preliminary scientific stories that aren’t peer-reviewed and, due to this fact, shouldn’t be considered conclusive, information medical observe/health-related habits, or handled as established data.

Journal reference:

  • Nielsen, Okay. et al. (2022) “Vaccine effectiveness against SARS-CoV-2 reinfection during periods of Alpha (B.1.1.7), Delta (B.1.617.2) or Omicron (B.1.1.529) dominance: A Danish nationwide study”. medRxiv. doi: 10.1101/2022.06.01.22275858. material/10.1101/2022.06.01.22275858v1

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