Table 1.

Characteristics and number of sera used in the validation of a measles avidity assay

Characteristic	No. of wk after vaccination or rash onset (IgM result)
	0 to 3 (+)	4 to 12 (+ or −)	13 to 18 (not tested)	>1 year (+ or −)
Group Aa
Confirmed measles cases	45	14	0	33
MMR1 recipients	31	50	0	31
Total	76	64	0	64
Group Bb
MMR1 recipientsc	0	0	8	0
Unvaccinated case, age younger than 9 monthsc	3	2	0	0
Outbreak immunization response recipientc	2	1	0	0
Collected during outbreaks in endemic settingsc
Unknown vaccination status	21	13	0	0
Unknown date of rash onsetd	0	4	0	0
Unvaccinated, unreliable information	6	0	0	0
Vaccinated with symptomse,f	0	0	0	20
Collected during outbreaks in elimination settingse
Unknown vaccination statusg	0	0	0	29
Unknown date of rash onseth	0	0	0	4
Unknown date of collection (both vaccinated)	0	0	0	2
Total	32	20	8	55

^aSamples for ROC analysis were distributed into two groups: (i) a recent-exposure group with previously unvaccinated measles IgM-positive persons aged ≥9 months collected 0 to 12 weeks after their first dose of measles, mumps, and rubella vaccine (MMR1) or after rash onset (samples collected at 0 to 3 weeks were used to select the low-avidity threshold, and samples collected at 0 to 12 weeks were used to select the high-avidity threshold) and (ii) a distant-exposure group with samples collected from IgM-negative adults more than a year after natural measles or vaccination and used to select both avidity thresholds.

^bSamples for ROC analysis were distributed into two groups: (i) a recent-exposure group with samples described in note c (samples collected at 0 to 3 weeks were used to select the low-avidity threshold, and samples collected at 0 to 18 weeks were used to select the high-avidity threshold) and (ii) a distant-exposure group with samples described in note f was used to select both avidity thresholds. Assumptions were made to use samples with uncertain epidemiological information. Groups A and B together make up group C.

^cRecent-exposure group for group B.

^dVaccination status was unknown for three individuals, and one was unvaccinated.

^eDistant-exposure group for group B.

^fSamples were collected 0 to 50 days after onset of rash.

^gSamples were collected −1 to 38 days after onset of rash.

^hVaccination status was unknown for three individuals, and one was vaccinated.