Hi, I am a nursing student at the University of Minnesota. I would like to help you smooth out the inconsistencies you are finding in regards to the post-vaccination varicella rash.
In all the research I have done to help answer your question I believe it is consistent to say that a post-vaccination varicella rash is contagious and they call this vaccine-virus transmission, however, it is very uncommon (http://www..science.mcmaster.ca/Biology/Virology/14/CHICVACC.HTM). The transmission rate of vaccine-virus varicella is 9%-28% (http://wonder..cdc.gov/wonder/preguid/p0000108/p0000108.htm). Furthermore, according to the research there is no evidence that a vaccine-virus is transmitted without a rash (http://www.ices.on.ca/docs/fb5490.htm). The chance of transmitting the vaccine-virus increases if the rash is vesicular lesions compared to papular lesions (LaRussa, Steinberg, Meurice, & Gershon (1997). Only 4% of kids vaccinated for varicella develop a generalized rash (median of 5 lesions 5-26 days post-vaccination) and only 4% develop a localized rash (median of 2 lesions 8-19 days post-vaccination-This rash may be maculo-papular with no vesicles (http://www.cdc.gov/nip/publications/manual/varicell.htm).
Although the post-vaccination rash is contagious it is important to note that most of the transmissions of the vaccine-virus has occured when the vacinee has been immunosuppressed. One study showed no transmission of the virus to immunosuppressed children from healthy children. However, a pregnant woman was infected from her vaccinated healthy child (http://www.science.mcmaster.ca/Biology/Virology/14/CHICVACC.HTM). I believe the above studies do show that there is still some uncertainty to how the transmission of vaccine-virus varicella occurs.
The only information I could find in regards to the rash returning is as follows: As I am sure you know second cases of varicella do occur, although rarely among immunologically normal persons. The virus remains in a latent state in the nerve tissue and may reactivate in 15% of affected persons as herpes zoster. Also there is what they call "Breakthrough disease" which is a case of wild type varicella infection occuring more that 42 days post-vaccination. The disease is mild and has usually fewer than 50 lesions (http://www.cdc.gov/nip/publications/manual/varicell.htm). I did not find any information on the vaccine-virus rash reappearing.
I did not find any specific information on whether or not a child can return to school with a post-vaccination varicella rash. One source states that if a child does develop a rash, the child should limit their exposure to high risk indiviuals (http://www.metrokc.gov/health/phnr/prot_res/vacscene/vol3022.htm). Another source states that the child with the rash carries a minimal risk of transmitting the virus to suseptible close contacts and that the rash should be covered (http://www.hc-sc.gc.ca/hpb/Icdc/publicat/;ccdr/99vol25/25sup/acs1.html). My opinion would be to first check with the school nurse and then to assess where the lesions are on the child's body. If the child has few lesions that are well covered and scabbing over he/she could perhaps go to school as long as the child is feeling well.
I would like to add that according to Georges (1996) an infection from the vaccine type virus is preferable to the wild-type virus and it is therefore reccommended for one to have the varicella vaccination.
Georges,P. (1996). More questions about varicella vaccination. The Pediactric Infectious Disease Journal, 15 (6), 560-1. http://wonder.cdc.gov/wonder/prevgui...8/p0000108.htm http://www.cdec.gov.nip/publications...l/varicell.htm http://www.hc-sc.gc.ca.hpb/Icdc/publ...5sup/acs1.html http://www.ices.on.ca/docs/fb5490.htm http://www.metrokc.gov/health/phnr/p...ne/vol3022.htm http://www.science.mcmaster.ca/Biolo...4/CHICVACC.HTM
LaRussa, P., Steinberg, S., Meurice, F., & Gershon, A. (1997). Transmission of vaccine strain varicella-zoster virus from a healthy adult with vaccine-associated rash to susceptible household contacts. Journal of Infectious Diseases, 176 (4), 1072-5.