Population Optimally Immunized after Accounting for Type-Specific COVID-19 Vaccine Waning Intervals: State-Level Prevalence and Trends

BACKGROUNDCOVID-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. METHODSWe 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.) RESULTSThe 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. CONCLUSIONSOur 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.