Top 5 Takeaways

  1. Effectiveness of Monovalent mRNA Vaccines: During the SARS-CoV-2 Omicron BA.1/BA.2 and BA.4/BA.5 periods, the effectiveness of three-dose monovalent mRNA vaccines against COVID-19–associated hospitalization waned over time.
  2. Vaccine Effectiveness Decrease: The study observed a decrease in effectiveness from 79% to 60% in the initial 120 days after the third dose, dropping further to 41% and 29%, respectively, after 120 days.
  3. Public Health Implication: This indicates the need for updated bivalent COVID-19 mRNA vaccines, especially to maximize protection against newer BA.4/BA.5 lineages and prevent COVID-19–associated hospitalization.
  4. Waning Protection: Vaccine-induced immunity wanes over time, more notably in the BA.4/BA.5 period, highlighting the importance of booster doses.
  5. Study Period and Methodology: The study was conducted from December 26, 2021, to August 31, 2022, across 18 states, utilizing a test-negative, case-control analysis within the IVY Network.

Original Article Author and Citation

Corresponding Author

Diya Surie,

Suggested Citation

Surie D, Bonnell L, Adams K, et al. Effectiveness of Monovalent mRNA Vaccines Against COVID-19–Associated Hospitalization Among Immunocompetent Adults During BA.1/BA.2 and BA.4/BA.5 Predominant Periods of SARS-CoV-2 Omicron Variant in the United States — IVY Network, 18 States, December 26, 2021–August 31, 2022. MMWR Morb Mortal Wkly Rep 2022;71:1327–1334. DOI: .


The study investigated the effectiveness of monovalent mRNA COVID-19 vaccines against hospitalization during the BA.1/BA.2 and BA.4/BA.5 periods. It found that vaccine effectiveness wanes significantly over time.


The research was conducted as a test-negative, case-control analysis within the IVY Network, involving adults aged ≥18 years. It compared vaccinated and unvaccinated groups for COVID-19–associated hospitalization.


The findings highlight the diminishing effectiveness of the monovalent mRNA vaccines over time, especially during the BA.4/BA.5 period. This decrease underlines the necessity of updated booster vaccines.


The study concludes that the effectiveness of monovalent mRNA COVID-19 vaccines against hospitalization wanes over time, emphasizing the importance of updated bivalent boosters for better protection against emerging SARS-CoV-2 lineages.


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