COVID-19 mRNA booster vaccines provided protection against severe COVID-19 caused by the Omicron variant for at least 6 months, and three doses of inactivated vaccines from China were more protective than two doses, but not as as protective as three doses of mRNA vaccines, finds a study from Singapore published today in JAMA Network Open.
Researchers at Singapore’s National Center for Infectious Diseases studied the effectiveness against infection and severe disease of two or more doses of the Pfizer/BioNTech or Moderna mRNA COVID-19 vaccines or the Chinese Sinovac inactivated COVID-19 vaccines , CoronaVac or Sinopharm. 2,441,581 residents aged 30 and over from December 27, 2021 to March 10, 2022, during Omicron’s dominance. Of all participants, 52.4% were women and 34.7% were 60 years or older.
A total of 90.2% of all participants received three doses of the COVID-19 vaccine at the end of the study period, 97.8% of them with an mRNA vaccine and 2.2% with an inactivated vaccine, while 9.8% had received only two doses, 93.8%. % with an mRNA vaccine.
mRNA vaccines were rolled out in Singapore in late 2020 and early 2021, while inactivated vaccines were not widely available until fall 2021. To meet vaccination requirements in Singapore, residents who receive three doses of inactivated vaccine should follow the series with an mRNA booster dose. .
A booster may be necessary after the inactivated vaccine series
Among the 2,441,581 participants, 319,943 (13.1%) tested positive for COVID-19 and 1,513 (0.4%) were severe infections.
The estimated vaccine effectiveness (VE) of an mRNA booster against Omicron infection was 31.7% to 41.3% after 15 to 60 days and declined rapidly over time. The estimated VE of mRNA boosting against severe COVID-19 was 87.4% and did not decrease up to 6 months. The estimated VE of three doses of inactivated vaccine against severe disease was 69.6%.
Five or more months after the booster dose, the estimated VE of mRNA against infection decreased, ranging from -2.8% to 14.6%. The estimated EV against severe disease was 87.4% (95% confidence interval). [CI]83.3% to 90.5%) 15 to 60 days after receiving an mRNA boost, falling slightly to 87.2% (95% CI, 84.2% to 89.7%) at 5 or 6 months, regardless of the vaccine combination.
The estimated effectiveness of three doses of inactivated COVID-19 vaccine against severe infections was 69.6% (95% CI, 48.7% to 81.9%) between 15 and 330 days, regardless of the combination More than 2 months after a third dose of inactivated vaccine, the effectiveness against infection was 12.5% (95% CI, 8.5% to 16.3%).
“We found that booster mRNA vaccination markedly increased protection against severe COVID-19 and was durable for at least a 6-month period, regardless of vaccine combination, suggesting that a fourth vaccine dose of mRNA is not necessary for adults without risk factors for additional protection against severe COVID-19 in this time frame,” the researchers wrote.
But because EV against Omicron infection declines rapidly after two and three doses of mRNA vaccine, a fourth dose of mRNA may increase protection, the authors said.
“Our results support the consideration of boosting after a 2- or 3-dose inactivated SARS-CoV-2 vaccine regimen,” they concluded. “Continued monitoring of booster efficacy over longer time intervals and in response to any other SARS-CoV-2 variant is crucial to determine optimal vaccination strategies against COVID-19.”