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Getting a third dose of either Pfizer-BioNTech's (PFE) or Moderna's (MRNA) COVID-19 vaccine offers a "significant increase" in protection against the Omicron variant in elderly people, according to a Danish study published on Wednesday.
The study, which is not yet peer-reviewed, investigated the effectiveness of COVID-19 vaccines that use so-called mRNA technology against the Delta variant and the new, more infectious Omicron variant.
"Our study contributes to emerging evidence that BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna) primary vaccine protection against Omicron decreases quickly over time, with booster vaccination offering a significant increase in protection," the authors wrote in the study.
The study was conducted by researchers at Denmark's top infectious disease authority, Statens Serum Institut (SSI). It analyzed data from three million Danes gathered between Nov. 20 and Dec. 12.
Among those who recently had their second vaccine dose, effectiveness against Omicron was measured at 55.2% for Pfizer-BioNTech and 36.7% for Moderna, compared to unvaccinated people.
But that protection quickly waned over the course of five months, the researchers said.
"We see that the protection is lower and decreases faster against Omicron than against the Delta variant after a primary vaccination course," study author Palle Valentiner-Branth said.
A third dose of Pfizer-BioNTech's vaccine, however, restored protection to 54.6% in people aged 60 or more who had been inoculated 14 to 44 days earlier, compared to those with only two doses.
The study confirms the findings of a recent British study, which also showed a rapid decline in protection against Omicron over time and an increase following a booster with Pfizer-BioNTech's vaccine.
"In light of the exponential rise in Omicron cases, these findings highlight the need for massive rollout of vaccinations and booster vaccinations," the researchers said.
Reporting by Nikolaj Skydsgaard Editing by Jacob Gronholt-Pedersen and Mark Potter.