Decline in cases of rotavirus gastroenteritis presenting to The Children's Hospital of Philadelphia after introduction of a pentavalent rotavirus vaccine

Abstract

A pentavalent rotavirus vaccine for infants became available in the United States in February 2006. By 2007, vaccination rates nationwide were estimated to be approximately 50%. We studied the effectiveness of the vaccine in a real-world setting outside of a clinical trial. All children presenting to The Children's Hospital of Philadelphia with acute gastroenteritis have been monitored for the presence of rotavirus antigen in the stool by enzyme-linked immunosorbent assay (ELISA [followed by genotyping if ELISA positive]) since the 1994-1995 epidemic season, presenting a unique opportunity to assess the impact of the recently introduced vaccine. The annual number of community-acquired cases over the preceding 13 years had approached or exceeded 100, with 271 cases in 2005 to 2006 and 167 cases in 2006 to 2007. In the 2007-2008 season, only 36 community-acquired cases were identified, representing an 87% reduction from the same period in 2005 to 2006. G3 was the predominant serotype, accounting for 15 community cases (42%). Our study is limited by its observational design using historical comparisons. Nonetheless, the abrupt decline in rotavirus gastroenteritis cases during the 2007-2008 season likely resulted from vaccination. Because protection rates appeared to have exceeded vaccination rates, herd immunity may have contributed to some degree to the effectiveness of the vaccine.

FIG. 1.

Number of community-acquired rotavirus cases presenting to CHOP for the last 14 rotavirus epidemic seasons (1994 to 2005 through 2007 to 2008). On the basis of historical experience, the rotavirus epidemic season in Philadelphia was considered to extend from December through the following June. The collection of samples was incomplete during the 2002-2003 rotavirus season, when only 29 of 175 ELISA-positive specimens were available for serotyping. During the 2007-2008 season, 36 community-acquired cases were seen at CHOP. For the preceding 13 seasons, the mean number of cases was 157 (95% confidence interval, 126 to 187) and the median number of cases was 167 (interquartile range, 106 to 184).

FIG. 2.

(A) Number of community-acquired rotavirus cases presenting to CHOP for the last four rotavirus epidemic seasons (from 2004 to 2005 through 2007 to 2008) by month. The total number of ELISA-confirmed rotavirus cases during the 2007-2008 season was 50, including 36 community-acquired and 14 nosocomial cases. Table 1 gives the VP7 serotypes of the community-acquired cases of rotavirus gastroenteritis presenting to CHOP over the last four epidemic seasons. (B) Seasonality of the rotavirus epidemic season prior to licensure of the pentavalent rotavirus vaccine. The overall percentage of ELISA-confirmed community-acquired cases of rotavirus gastroenteritis presenting to CHOP is shown by month for the combined seasons from 1994 to 1995 through 2005 to 2006. The peak annual incidence was generally seen in March.

FIG. 3.

Age distribution of community-acquired rotavirus cases presenting to CHOP during the 2007-2008 epidemic season. m, months; y, years. For 13 years prior to the 2007-2008 season, the median age of children seen at CHOP with rotavirus gastroenteritis ranged from 8 to 14 months. The median age of cases during the 2007-2008 season was 20 months.

FIG. 4.

Serotype distribution of community-acquired rotavirus cases presenting to CHOP during the 2007-2008 epidemic season. Genotyping of the 36 community isolates in 2007 to 2008 revealed 10 cases of G1P1A[8]; 14 cases of G3P1A[8]; 3 cases of (G-nontypeable)P1A[8]; and 1 case each of G1P1B[4], G2P1A[8], G2P1B[4], G2/QNS (QNS, quantity not sufficient), G3(P-nontypeable), G4P1A[8], G9P1A[8], G12P1A[8], and nontypeable. Genotyping of the 14 nosocomial cases in 2007 to 2008 revealed 2 cases of G2P1B[4]; 7 cases of G3P1A[8]; 2 cases of (G-nontypeable)P1A[8]; and 1 case each of G1P1A[8], G2(P-nontypeable), and nontypeable. All serotypes causing nosocomial infections appeared earlier in the community.