Abstract To directly compare serum rotavirus specific IgA as a marker of protection in children vaccinated with the RRV‐TV (Rotashield™) vaccine and in naturally infected children, we studied pre‐existing rotavirus IgA antibodies by ELISA assays in these groups of children within the first 5 days after the onset of a diarrhea episode, due or not to rotavirus. In immunized children, rotavirus IgA titers were similar between infected and non‐RV infected children. In non‐immunized children, the proportion with rotavirus IgA titers was significantly greater in non‐RV infected children (58%) than in infected children (31%). Additionally, a titer ≥1:800 was associated with 68% protection. Thus, in this study serum rotavirus IgA showed a good correlation with protection in children pre‐exposed to natural infection but not in those immunized with the RRV‐TV vaccine. J. Med. Virol. 76:608–612, 2005. © 2005 Wiley‐Liss, Inc.