In a recent study published on the medRxiv * preprint server, researchers evaluated the effectiveness of coronavirus vaccines 2019 (COVID-19) against COVID-19 infections and related hospitalizations.
Study: Efficacy of the vaccine against SARS-CoV-2 infection and COVID-19-related hospitalization with SARS-CoV-2 variants Alpha, Delta and Omicron: a nationwide Danish cohort study. Image credit: insta_photos / Shutterstock
Vaccines against severe acute coronavirus 2 syndrome (SARS-CoV-2) have played a crucial role in reducing pandemic-related mortality and morbidity. However, emerging reports of breakthrough infections with SARS-CoV-2 pose a new public health challenge.
About the study
In the present study, the researchers evaluated the effectiveness of two and three doses of COVID-19 ribonucleic acid (mRNA) vaccines against SARS-CoV-2 alpha, delta and variant infection with Omicron variant and associated hospitalization.
The study population included residents of Denmark aged 12 or over over a period of time where Alpha, Delta or Omicron variants were dominant. The team included only the first SARS-CoV-2 positive polymerase chain reaction (PCR) test per participant. They received information on all laboratory-confirmed positive results of reverse transcription-PCR (RT-PCR) from the Danish Microbiological Database (MiBa). COVID-19-related hospitalization is defined as a new hospital admission lasting at least 12 hours, occurring within two days before or 14 days after diagnosis of SARS-CoV-2 Alpha, Delta or Omicron infection.
The time from vaccination to the first diagnosis of symptomatic or asymptomatic SARS-CoV-2 infection or SARS-CoV-2-related hospital admission was analyzed according to three periods in which the dominant variant was found in 75% of those confirmed by RT. -PCR cases: (1) Alpha period from February 20 to June 15, 2021; (2) Delta period from 4 July to 20 November 2021; and (3) the Omicron period from 21 December 2021 to 31 January 2022.
The team monitored vaccinated participants from the start of the study or 14 days after vaccination, which is the date of predicted protection induced after the second or third dose of vaccine. Follow-up continued until the participant reported SARS-CoV-2 infection, booster vaccination, emigration, completion of the study period, or death, whichever came first. Unvaccinated participants were followed from the start of the study to the date of their first vaccination, emigration, SARS-CoV-2 diagnosis, end of study, or death, whichever came first.
Results
The results of the study show that during the period of dominance of SARS-CoV-2 Delta, fewer people aged 60 and over were unvaccinated compared to those during the Alpha period. During the Omicron period, the majority of people aged 12 to 60 and 60 years and older were vaccinated with two or three doses of the vaccine. As of January 31, 2022, 85% of people between the ages of 12 and 59 and 95% of people aged 60 and over have been vaccinated with two doses. While on the same date, almost 64% and 90% of people aged 18 to 59 and 60 and older received three doses, respectively.
Among individuals 60 years of age and older, the effectiveness of the vaccine against infection after two doses was 91% 14 to 30 days after and 71.5% 120 days after vaccination during the Alpha period and 82.2% 14 to 30 days after and 49.8% 120 days after vaccination during the Delta period. Among participants aged 12 to 59 years, the effectiveness of the vaccine against infection after two doses was 92.2% 14 to 30 days after 64.9% 120 days after vaccination during the Delta period and 39.8% 14 to 30 days after 13.2% 120 days after vaccination during the Omicron period.
Among participants aged 18 to 59 years, the effectiveness of the vaccine against infection after three doses was 89.5% 14 to 30 days after and 83.5% 61 to 90 days after vaccination during the Delta period and 55.2% 14 up to 30 days after and 49.9% 120 days after vaccination during the Omicron period. Among participants aged 60 years and older, the effectiveness of the vaccine against infection after three doses was 57.6% 14 to 30 days after and 52.8% 120 days after vaccination during the Omicron period.
Among subjects 60 years of age and older, the effectiveness of the vaccine against hospitalization with SARS-CoV-2 Alpha or Delta variants after two doses of vaccine was 96.4% and 100%, respectively, 14 to 30 days after vaccination. More than 120 days after vaccination, the effectiveness of the hospitalization vaccine decreased to 90.5% for alpha and 86.2% for delta infections. Among individuals 60 years of age and older, the efficacy of the vaccine against hospitalization after Delta infection was 96.6% 14 to 30 days after and 91.4% 61 to 90 days after three-dose vaccination. On the other hand, among people aged 18 to 59 years, the effectiveness of the Delta vaccine was 94.8% 14 to 30 days after and 68.4% 31 to 60 days after three-dose vaccination.
Overall, the results of the study showed that vaccination with a third dose of mRNA increased protection against infection and associated hospitalization, especially against the SARS-CoV-2 Omicron variant.
*Important message
medRxiv publishes preliminary scientific reports that are not reviewed by partners and therefore should not be considered convincing, guide clinical practice / health-related behavior, or be treated as established information.
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