Population Optimally Immunized after Accounting for Type-Specific COVID-19 Vaccine Waning Intervals: State-Level Prevalence and Trends
BACKGROUND: COVID-19 vaccines exhibit real-world waning effectiveness against SARS-CoV-2 infection within the first 3-6 months after a completed series. Consequently, the main metric tracked by the CDC (percent "fully vaccinated," with no adjustment for booster status) has become insufficiently informative. METHODS: We analyzed CDC daily vaccination data to quantify COVID-19 immunization status for 4 mutually-exclusive groups: (1) not immunized; (2) partially immunized (people who received the 1st dose of a 2-dose series); (3) immunized with waning immunity (previously immunized people whose booster dose is overdue); and (4) optimally immunized (people who: (a) received the Janssen vaccine <2 months ago or completed an mRNA vaccine series <6 months ago, or (b) received the Janssen vaccine >2 months ago or completed an mRNA vaccine series >6 months ago and received a booster dose.) RESULTS: The proportion of the total US population who were optimally immunized against COVID-19 fell from a high of 45.3% on July 17 to 29.4% on November 30. During November, the majority of states experienced a worsening trend in the percent of the total population who were overdue for a booster dose, including the 4 largest states, with percentage point increases of 3.5 in New York, 3.4 in California, 2.3 in Texas and 1.7 in Florida. CONCLUSIONS: Our proposed classification scheme accounts for type-specific vaccine waning intervals, provides an accurate assessment of progress toward national immunization goals, and reveals the urgent need for additional public health mitigation strategies to successfully combat the COVID-19 pandemic in the United States.