TABLE 2. Monovalent vaccine effectiveness against symptomatic SARS-CoV-2 infection among young children, by vaccine product, number of doses, and time since last dose — Increasing Community Access to Testing program, United States, July 2022–February 2023.

Vaccine product, age group, analysis period,* no. of doses (time since last dose)†,§	No. (%) of positive test results	No. (%) of negative test results	VE¶ (95% CI)
Monovalent Moderna COVID-19 vaccine, children aged 3–5 yrs
1-dose VE analysis, Jul 4, 2022–Feb 5, 2023
Unvaccinated (Ref)	9,523 (27)	25,459 (73)	Ref
1 dose only (2 wks–1 mo)	107 (21)	402 (79)	40 (26 to 52)
2-dose VE analysis, Aug 1, 2022–Feb 5, 2023
Unvaccinated (Ref)	5,690 (23)	19,359 (77)	Ref
2 doses
2 doses (2 wks–2 mos)	81 (10)	735 (90)	60 (49 to 68)
2 doses (3–4 mos)	58 (12)	437 (88)	36 (15 to 52)
2 doses (5–6 mos)**	NA	NA	NA
Monovalent Pfizer-BioNTech COVID-19 vaccine, children aged 3–4 yrs
1-dose VE analysis, Jul 4, 2022–Feb 5, 2023
Unvaccinated (Ref)	6,212 (28)	16,111 (72)	Ref
1 dose only (2 wks–1 mo)	114 (26)	329 (74)	19 (−1 to 35)
2-dose VE analysis, Jul 25, 2022–Feb 5, 2023
Unvaccinated (Ref)	4,298 (25)	13,136 (75)	Ref
2 doses only (2 wks–3 mos)	137 (15)	796 (85)	40 (28 to 50)
3-dose VE analysis, Sep 19, 2022–Feb 5, 2023 ††
Unvaccinated (Ref)	1,273 (17)	6,275 (83)	Ref
3 doses only (2 wks–4 mos)	53 (13)	342 (87)	31 (7 to 49)

Abbreviations: NA = not applicable; Ref = referent group; VE = vaccine effectiveness.

* Different analysis periods were used for each vaccine product and dose number. Children became eligible to be included in each analysis 2 weeks after the initial date a child could have received each vaccine product and dose combination: 1 dose of Moderna and Pfizer-BioNTech on July 4, 2022; 2 doses of Pfizer-BioNTech on July 25, 2022; 2 doses of Moderna on August 1, 2022; and 3 doses of Pfizer-BioNTech on September 19, 2022.

^† Only month and year of receipt of each vaccine dose were reported from some participating pharmacies; therefore, the number of months between a vaccine dose and testing is a whole number calculated as the difference between the month and year of testing and the month and year of the vaccine dose. Tests from children for whom receipt of a third COVID-19 vaccine dose on or after December 2022 (when bivalent COVID-19 vaccine doses were recommended for this age group) was reported were excluded.

^§ For doses received in the same month or the month before SARS-CoV-2 testing, an additional question was asked to ascertain whether the dose was received ≥2 weeks before testing if the most recent vaccination date included only month and year. Only doses received ≥2 weeks before testing were included.

^¶ VE = (1 − adjusted odds ratio) x 100. Odds ratios were calculated using multivariable logistic regression, adjusting for single year of age, gender, race, ethnicity, Social Vulnerability Index of the testing location, underlying conditions (presence versus absence), U.S. Department of Health and Human Services region of testing site, pharmacy chain conducting the test, local incidence (cases per 100,000 population by site county in the 7 days before test date), and testing calendar date.

** Moderna 2 dose VE at 5–6 months after receipt of the second dose did not meet precision threshold as CI width >50 percentage points, and thus data are not shown. Among second dose recipients, 165 and 43 children received a second dose of Moderna vaccine 5 months and 6 months before testing, respectively.

^†† Pfizer-BioNTech 3-dose VE estimates did not have sufficient power to stratify by time since vaccination.