Outbreak of influenza type A (H1N1) in Iporanga, São Paulo State, Brazil

• Main Authors: Terezinha Maria de PAIVA, Maria Akiko ISHIDA, Kazue Aparecida Yamamoto HANASHIRO, Regina Maria SCOLARO, Maria Gisele GONÇALVES, Margareth Aparecida BENEGA, Meire Aparecida S. OLIVEIRA, Aurea Silveira CRUZ, Sueko TAKIMOTO
• Format: Article in Journal/Newspaper
• Language: English
• Published: Universidade de São Paulo (USP) 2001
• Subjects: Influenza virus; Influenza surveillance; Influenza vaccine; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doaj.org/article/17b7f4d11b5f4d17b832672e7d0798a1

From June to July 1999 an outbreak of acute respiratory illness occurred in the town of Iporanga. Out of a total of 4,837 inhabitants, 324 cases were notified to the Regional Surveillance Service. Influenza virus was isolated from 57.1% of the collected samples and 100% seroconversion to influenza A (H1N1) was obtained in 20 paired sera tested. The isolates were related to the A/Bayern/07/95 strain (H1N1). The percentages of cases notified during the outbreak were 28.4%, 29.0%, 20.7%, 6.2% and 15.7% in the age groups of 0-4, 5-9, 10-14, 15-19 and older than 20 years, respectively. The highest proportion of positives was observed among children younger than 14 years and no cases were notified in people older than 65 years, none of whom had been recently vaccinated against influenza. These findings suggest a significant vaccine protection against A/Bayern/7/95, the H1 component included in the 1997-98 influenza vaccine for elderly people. This viral strain is antigenically and genetically related to A/Beijing/262/95, the H1 component of the 1999 vaccine. Vaccines containing A/Beijing/262/95 (H1N1) stimulated post-immunization hemagglutination inhibition antibodies equivalent in frequency and titre to both A/Beijing/262/95-like and A/Bayern/7/95-like viruses. Thus, this investigation demonstrates the effectiveness of vaccination against influenza virus in the elderly.