The efficacy of COVID-19 vaccine booster shots against symptomatic cases of the Omicron variant wanes significantly after 10 weeks, according to new data from the UK.
In the report, the UK Health Security Agency said, “Among those who received an AstraZeneca primary course, vaccine effectiveness was around 60% 2 to 4 weeks after either a Pfizer or Moderna booster, then dropped to 35% with a Pfizer booster and 45% with a Moderna booster by 10 weeks after the booster. Among those who received a Pfizer primary course, vaccine effectiveness was around 70% after a Pfizer booster, dropping to 45% after 10-plus weeks and stayed around 70 to 75% after a Moderna booster up to 9 weeks after booster.”
The report warned that other factors could have affected the results of the study.
“These results should be interpreted with caution due to the low counts and the possible biases related to the populations with highest exposure to Omicron (including travelers and their close contacts) which cannot fully be accounted for,” the report said.
According to the report, “There are insufficient severe cases of Omicron as yet to analyze vaccine effectiveness against hospitalization, but this is expected to be better sustained, for both primary and booster doses.”
However, the report said that the Omicron variant appears to be significantly less severe than the Delta variant, with similar findings to studies from Scotland and South Africa.
“The University of Edinburgh study, drawing on the health records of 5.4 million people in Scotland, found the risk of hospitalization with Covid-19 was two-thirds lower with Omicron than with Delta. The new variant became dominant in Scotland last week,” the Wall Street Journal reported. “A separate study published online by researchers at South Africa’s National Institute for Communicable Diseases similarly found people infected with Omicron were 70% to 80% less likely to need hospital treatment than people infected with earlier variants, including Delta.”
