Table 6.

Interpretation and application of measles avidity results obtained in the absence of vaccination within 10 days of rash onset and from samples collected within the first 8 weeks

Avidity	IgM	Clinical and epidemiological information			Application
		Symptoms	Exposure	Infection history
Lowa	Pb or Nc	Classic	Wild type	Unvaccinated; no history	Confirms as measles
Low	P or N	Classic	Wild type	Unvaccinated; wild typed	Confirms as measles
Low	P	Classic	Unknown	Vaccinatede; no history	Confirms as measles
Low	P	Classic	Wild type	Vaccinated	Classifies as PVF
Highf	P or N	Classic	Wild type	Vaccinated	Classifies as SVF
High	P or N	Modified	Wild type	Vaccinated	Classifies as SVF
High	N	Fever; rash	Recent MMR2g	Vaccinated	Confirms previous exposure
High	P or N	Modified	Wild type	Previous wild-type exposureh	Confirms previous exposure

^aLow avidity is interpreted as primary immune response and is diagnostic for acute classic measles.

^bP, positive result. IgM is usually positive from days 3 to 28.

^cN, negative result. Avidity testing extends the opportunity to identify cases up to 8 weeks.

^dMay have been misdiagnosed initially; consider contagious.

^eVaccination in the distant past (at least 1 year).

^fHigh avidity is interpreted as a secondary immune response.

^gSymptoms are side effects from second MMR vaccine dose.

^hRare event; likely not contagious.