The third Covid-19 vaccine dose increases the level and duration of protection against the Omicron variant and hospitalisation compared to two vaccine doses, finds a new study. The study, published in the journal PLOS Medicine, showed that two vaccine doses provide only limited and short-lived protection against SARS-CoV-2 infection with the variant.
"Our findings indicate that a third dose is necessary to maintain protection against infection for a longer time and to ensure a high level of protection against Covid-19 hospitalisation with the Omicron variant," said researcher Mie Agermose Gram at Statens Serum Institut, Copenhagen, Denmark.
"Continued emergence of new variants and waning vaccine durability requires ongoing evaluation of vaccine effectiveness against infection and hospitalisation to inform future vaccination strategies," Gram added.
The emergence of new SARS-CoV-2 variants may decrease long-term vaccine durability, increasing the risk of infection and hospitalization. However, evidence is limited regarding the vaccine effectiveness of three vaccines over time.
For this study, the team conducted a nationwide cohort study of all previously uninfected Danish residents aged 12 and older by accessing individual-level data. The researchers then estimated vaccine effectiveness using vaccination status as a time-varying exposure, adjusting for age, sex, geographic location, and comorbidities before comparing infection and hospitalisation rates to unvaccinated individuals.
The researchers found that a third vaccine dose provided greater protection against infection and hospitalisation from the Omicron variant than with two vaccines and also that there was less evidence of waning protection.