Treyfish
Moderator
Update: Influenza Activity --- United States and Worldwide, 2006--07 Season, and Composition of the 2007--08 Influenza Vaccine
During the 2006--07 season, influenza activity peaked in mid-February in the United States and was associated with less mortality and lower rates of pediatric hospitalizations than during the previous three seasons. In the United States, influenza A (H1) viruses predominated overall, but influenza A (H3) viruses were isolated more frequently than influenza A (H1) viruses late in the season. Although influenza A (H1), A (H3), and B viruses cocirculated worldwide, influenza A (H3) viruses were the most commonly reported type in Europe and Asia. Sporadic cases of avian influenza A (H5N1) virus infections associated with severe illness or death were reported among humans in Cambodia, China, Egypt, Indonesia, Laos, Nigeria, and Viet Nam. This report summarizes influenza activity in the United States and worldwide during the 2006--07 influenza season (October 1, 2006--May 19, 2007) and describes the composition of the 2007--08 influenza vaccine. United States
The national percentage of respiratory specimens testing positive for influenza and the proportion of outpatient visits to sentinel providers for influenza-like illness (ILI)* peaked in mid-February. Although influenza A (H1) viruses were most commonly isolated overall, influenza A (H3) viruses were more frequently identified than influenza A (H1) viruses from early March through May. A small number of influenza B viruses also were identified. Viral Surveillance
During October 1, 2006--May 19, 2007, World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories in the United States tested 179,268 respiratory specimens for influenza viruses; 23,753 (13.2%) were positive (Figure 1). Of these, 18,817 (79.2%) were influenza A viruses and 4,936 (20.8%) were influenza B viruses. Among the influenza A viruses, 6,280 (33.4%) were subtyped; 3,912 (62.3%) were influenza A (H1) viruses and 2,368 (37.7%) were influenza A (H3) viruses. The proportion of specimens testing positive for influenza first exceeded 10% during the week ending December 23, 2006 (week 51), peaked at 28.0% during the week ending February 10, 2007 (week 6), and declined to less than 10% during the week ending April 28, 2007 (week 17). The proportion was above 10% positive for 14 consecutive weeks. The peak percentage of specimens testing positive for influenza during the previous three seasons ranged from 22.6% to 34.7%, and the peak occurred during early December to early March (1; CDC, unpublished data, 2007). During the previous three influenza seasons, the number of consecutive weeks during which more than 10% of specimens tested positive for influenza ranged from 13 to 17 weeks (1; CDC, unpublished data, 2007). Composition of the Influenza Vaccine for the 2007--08 Season
The Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee recommended that the 2007--08 trivalent influenza vaccine for the United States contain A/Solomon Islands/3/2006-like (H1N1), A/Wisconsin/67/2005-like (H3N2), and B/Malaysia/2506/2004-like viruses. This represents a change only in the influenza A (H1N1) component. A/Solomon Islands/3/2006 is a recent antigenic variant of the 2006--07 vaccine strain A/New Caledonia/20/99. The influenza A (H3N2) and influenza B components remain the same. These recommendations were based on antigenic analyses of recently isolated influenza viruses, epidemiologic data, postvaccination serologic studies in humans, and the availability of candidate vaccine strains and reagents. Antigenic Characterization
Since October 1, 2006, CDC has antigenically characterized 1,107 influenza viruses collected by U.S. laboratories: 486 influenza A (H1) viruses, 289 influenza A (H3) viruses, and 332 influenza B viruses. Of the 486 influenza A (H1) viruses, 439 (90%) were characterized as similar to A/New Caledonia/20/99, the influenza A (H1N1) component recommended for the 2006--07 influenza vaccine. Forty-five (9%) viruses showed reduced titers with antisera produced against A/New Caledonia/20/99 and are similar to A/Solomon Islands/3/2006, which is a recent antigenic variant of A/New Caledonia/20/99 and is the influenza A (H1N1) component recommended for the 2007--08 influenza vaccine. Two influenza A (H1) viruses showed reduced titers with antisera produced against both A/New Caledonia/20/99 and A/Solomon Islands/3/2006. Of the 289 influenza A (H3) viruses, 69 (24%) were characterized as similar to A/Wisconsin/67/2005, the H3N2 component recommended for the 2007--08 vaccine, and 220 (76%) of the 289 viruses showed reduced titers with antisera produced against A/Wisconsin/67/2005. Influenza B viruses currently circulating can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/02/87 viruses. A total of 254 (77%) of the 332 influenza B viruses that have been characterized belong to the B/Victoria lineage: 128 (50%) were similar to B/Ohio/01/2005, and 126 (50%) showed reduced titers with antisera produced against B/Ohio/01/2005. B/Ohio/01/2005 is antigenically equivalent to B/Malaysia/2506/2004, the recommended influenza B component for the 2007--08 influenza vaccine. Seventy-eight (23%) of the 332 influenza B viruses were identified as belonging to the B/Yamagata lineage. Influenza-Like Illness (ILI) Surveillance
The weekly percentage of patient visits to U.S. sentinel providers for ILI exceeded or was at baseline levels (2.1%)<SUP>?</SUP> during the weeks ending December 16, 2006--March 24, 2007 (weeks 50--12) and peaked twice, once at 3.0% for the week ending December 30, 2006 (week 52), and again at 3.5% for the week ending February 17, 2007 (week 7) (Figure 2). The increase in the percentage of patient visits for ILI during the week ending December 30, 2006 (week 52) might have been influenced by a reduction in routine health-care visits during the holiday season, as has occurred in previous seasons. During the previous three influenza seasons, the peak percentage of patient visits for ILI has ranged from 3.3% to 7.6% and the peak occurred during late December to mid-February (1; CDC, unpublished data, 2007). State-Specific Activity Levels
State and territorial epidemiologists report the geographic distribution of influenza in their state through a weekly influenza activity code. The geographic distribution of influenza activity peaked during the week ending February 24, 2007 (week 8), when 25 states reported widespread activity and 19 states reported regional activity.<SUP>? </SUP>Forty-one states reported widespread influenza activity at least once during the 2006--07 season. No states reported widespread influenza activity during the weeks ending April 21--May 19, 2007 (weeks 16--20). The peak number of states reporting widespread or regional activity during the previous three seasons ranged from 41 to 50 states (1; CDC, unpublished data, 2007). Influenza-Associated Pediatric Hospitalization
Pediatric hospitalizations associated with laboratory-confirmed influenza infections are monitored in two population-based surveillance networks: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN). During October 1, 2006--April 28, 2007, the preliminary influenza-associated hospitalization rate reported by EIP for children aged 0--17 years was 0.81 per 10,000. For children aged 0--4 years and 5--17 years, the rates were 1.62 per 10,000 and 0.23 per 10,000, respectively. During November 5, 2006--May 26, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate for children aged 0--4 years in NVSN was 3.46 per 10,000. EIP hospitalization data collection ended on April 28, 2007, whereas NVSN hospitalization data collection ended on May 26, 2007. Rate estimates are preliminary and might continue to change as data are finalized.
In years 2000--2006, the end-of-season hospitalization rate for NVSN ranged from 3.7 (2002--03) to 12 (2003--04) per 10,000 children aged 0--4 years. During the 2004--05 influenza season, the end-of-season hospitalization rate for EIP was 3.3 per 10,000 children aged 0--4 years and 0.6 per 10,000 children aged 5--17 years; during the 2005--06 season, the rates were 2.8 and 0.4, respectively. Differences in rate estimates between the NVSN and the EIP systems likely result from different case-finding methods, the diagnostic tests used, and the populations monitored.<SUP>?</SUP> Pneumonia- and Influenza-Related Mortality
During the 2006--07 influenza season, the percentage of deaths attributed to pneumonia and influenza (P&I) did not exceed the epidemic threshold** in the 122 Cities Mortality Reporting System (Figure 3). The percentage of P&I deaths peaked three times, once at 7.5% during the week ending January 20, 2007 (week 3), once at 7.7% during the week ending February 24, 2007 (week 8), and again at 7.5% during the week ending March 24, 2007 (week 12). During the previous three influenza seasons, the peak percentage of P&I deaths ranged from 7.8% to 10.4%, and the total number of weeks above the epidemic threshold ranged from one to 16 (1; CDC, unpublished data, 2007). Influenza-Associated Pediatric Mortality
As of August 6, 2007, among persons aged <18 years, a total of 68 deaths associated with influenza infection occurring during October 1, 2006--May 19, 2007, were reported to CDC. These deaths were reported from 26 states (Alabama, Alaska, Arizona, California, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Kansas, Louisiana, Minnesota, North Carolina, Nebraska, Nevada, New Mexico, New York, Ohio, Oklahoma, South Dakota, Tennessee, Texas, Virginia, Washington, and Wisconsin). All patients had laboratory-confirmed influenza virus infection. Age-specific information was available for all 68 persons; 10 were aged <6 months, 10 were aged 6--23 months, nine were aged 2--4 years, and 39 were aged 5--17 years. Of the 63 patients for whom influenza virus type was known, 47 had influenza A and 16 had influenza B viruses. Of the 53 patients aged >6 months for whom vaccination status was known, 50 (94%) had not been vaccinated against influenza. These data are provisional. Worldwide
During the 2006--07 influenza season, influenza A (H1), A (H3), and B viruses cocirculated worldwide. In Africa, small numbers of influenza A and B viruses were reported. In Europe and Asia, influenza A (H3) viruses were identified most frequently, but influenza A (H1) viruses circulated at low levels. Influenza B viruses circulated at lower levels overall in Asia and Europe but predominated in some countries. Human Infections with Avian Influenza A (H5N1) Viruses
From December 1, 2003, through July 25, 2007, a total of 319 human cases of avian influenza A (H5N1) infection were reported to WHO (2). Of these, 192 (60%) were fatal (Table). All cases were reported from Asia (Azerbaijan, Cambodia, China, Indonesia, Iraq, Laos, Thailand, Turkey, and Viet Nam) and Africa (Djibouti, Egypt, and Nigeria). To date, no human case of avian influenza A (H5N1) virus infection has been identified in the United States. <snip>:tiphat: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5631a2.htm
During the 2006--07 season, influenza activity peaked in mid-February in the United States and was associated with less mortality and lower rates of pediatric hospitalizations than during the previous three seasons. In the United States, influenza A (H1) viruses predominated overall, but influenza A (H3) viruses were isolated more frequently than influenza A (H1) viruses late in the season. Although influenza A (H1), A (H3), and B viruses cocirculated worldwide, influenza A (H3) viruses were the most commonly reported type in Europe and Asia. Sporadic cases of avian influenza A (H5N1) virus infections associated with severe illness or death were reported among humans in Cambodia, China, Egypt, Indonesia, Laos, Nigeria, and Viet Nam. This report summarizes influenza activity in the United States and worldwide during the 2006--07 influenza season (October 1, 2006--May 19, 2007) and describes the composition of the 2007--08 influenza vaccine. United States
The national percentage of respiratory specimens testing positive for influenza and the proportion of outpatient visits to sentinel providers for influenza-like illness (ILI)* peaked in mid-February. Although influenza A (H1) viruses were most commonly isolated overall, influenza A (H3) viruses were more frequently identified than influenza A (H1) viruses from early March through May. A small number of influenza B viruses also were identified. Viral Surveillance
During October 1, 2006--May 19, 2007, World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories in the United States tested 179,268 respiratory specimens for influenza viruses; 23,753 (13.2%) were positive (Figure 1). Of these, 18,817 (79.2%) were influenza A viruses and 4,936 (20.8%) were influenza B viruses. Among the influenza A viruses, 6,280 (33.4%) were subtyped; 3,912 (62.3%) were influenza A (H1) viruses and 2,368 (37.7%) were influenza A (H3) viruses. The proportion of specimens testing positive for influenza first exceeded 10% during the week ending December 23, 2006 (week 51), peaked at 28.0% during the week ending February 10, 2007 (week 6), and declined to less than 10% during the week ending April 28, 2007 (week 17). The proportion was above 10% positive for 14 consecutive weeks. The peak percentage of specimens testing positive for influenza during the previous three seasons ranged from 22.6% to 34.7%, and the peak occurred during early December to early March (1; CDC, unpublished data, 2007). During the previous three influenza seasons, the number of consecutive weeks during which more than 10% of specimens tested positive for influenza ranged from 13 to 17 weeks (1; CDC, unpublished data, 2007). Composition of the Influenza Vaccine for the 2007--08 Season
The Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee recommended that the 2007--08 trivalent influenza vaccine for the United States contain A/Solomon Islands/3/2006-like (H1N1), A/Wisconsin/67/2005-like (H3N2), and B/Malaysia/2506/2004-like viruses. This represents a change only in the influenza A (H1N1) component. A/Solomon Islands/3/2006 is a recent antigenic variant of the 2006--07 vaccine strain A/New Caledonia/20/99. The influenza A (H3N2) and influenza B components remain the same. These recommendations were based on antigenic analyses of recently isolated influenza viruses, epidemiologic data, postvaccination serologic studies in humans, and the availability of candidate vaccine strains and reagents. Antigenic Characterization
Since October 1, 2006, CDC has antigenically characterized 1,107 influenza viruses collected by U.S. laboratories: 486 influenza A (H1) viruses, 289 influenza A (H3) viruses, and 332 influenza B viruses. Of the 486 influenza A (H1) viruses, 439 (90%) were characterized as similar to A/New Caledonia/20/99, the influenza A (H1N1) component recommended for the 2006--07 influenza vaccine. Forty-five (9%) viruses showed reduced titers with antisera produced against A/New Caledonia/20/99 and are similar to A/Solomon Islands/3/2006, which is a recent antigenic variant of A/New Caledonia/20/99 and is the influenza A (H1N1) component recommended for the 2007--08 influenza vaccine. Two influenza A (H1) viruses showed reduced titers with antisera produced against both A/New Caledonia/20/99 and A/Solomon Islands/3/2006. Of the 289 influenza A (H3) viruses, 69 (24%) were characterized as similar to A/Wisconsin/67/2005, the H3N2 component recommended for the 2007--08 vaccine, and 220 (76%) of the 289 viruses showed reduced titers with antisera produced against A/Wisconsin/67/2005. Influenza B viruses currently circulating can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/02/87 viruses. A total of 254 (77%) of the 332 influenza B viruses that have been characterized belong to the B/Victoria lineage: 128 (50%) were similar to B/Ohio/01/2005, and 126 (50%) showed reduced titers with antisera produced against B/Ohio/01/2005. B/Ohio/01/2005 is antigenically equivalent to B/Malaysia/2506/2004, the recommended influenza B component for the 2007--08 influenza vaccine. Seventy-eight (23%) of the 332 influenza B viruses were identified as belonging to the B/Yamagata lineage. Influenza-Like Illness (ILI) Surveillance
The weekly percentage of patient visits to U.S. sentinel providers for ILI exceeded or was at baseline levels (2.1%)<SUP>?</SUP> during the weeks ending December 16, 2006--March 24, 2007 (weeks 50--12) and peaked twice, once at 3.0% for the week ending December 30, 2006 (week 52), and again at 3.5% for the week ending February 17, 2007 (week 7) (Figure 2). The increase in the percentage of patient visits for ILI during the week ending December 30, 2006 (week 52) might have been influenced by a reduction in routine health-care visits during the holiday season, as has occurred in previous seasons. During the previous three influenza seasons, the peak percentage of patient visits for ILI has ranged from 3.3% to 7.6% and the peak occurred during late December to mid-February (1; CDC, unpublished data, 2007). State-Specific Activity Levels
State and territorial epidemiologists report the geographic distribution of influenza in their state through a weekly influenza activity code. The geographic distribution of influenza activity peaked during the week ending February 24, 2007 (week 8), when 25 states reported widespread activity and 19 states reported regional activity.<SUP>? </SUP>Forty-one states reported widespread influenza activity at least once during the 2006--07 season. No states reported widespread influenza activity during the weeks ending April 21--May 19, 2007 (weeks 16--20). The peak number of states reporting widespread or regional activity during the previous three seasons ranged from 41 to 50 states (1; CDC, unpublished data, 2007). Influenza-Associated Pediatric Hospitalization
Pediatric hospitalizations associated with laboratory-confirmed influenza infections are monitored in two population-based surveillance networks: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN). During October 1, 2006--April 28, 2007, the preliminary influenza-associated hospitalization rate reported by EIP for children aged 0--17 years was 0.81 per 10,000. For children aged 0--4 years and 5--17 years, the rates were 1.62 per 10,000 and 0.23 per 10,000, respectively. During November 5, 2006--May 26, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate for children aged 0--4 years in NVSN was 3.46 per 10,000. EIP hospitalization data collection ended on April 28, 2007, whereas NVSN hospitalization data collection ended on May 26, 2007. Rate estimates are preliminary and might continue to change as data are finalized.
In years 2000--2006, the end-of-season hospitalization rate for NVSN ranged from 3.7 (2002--03) to 12 (2003--04) per 10,000 children aged 0--4 years. During the 2004--05 influenza season, the end-of-season hospitalization rate for EIP was 3.3 per 10,000 children aged 0--4 years and 0.6 per 10,000 children aged 5--17 years; during the 2005--06 season, the rates were 2.8 and 0.4, respectively. Differences in rate estimates between the NVSN and the EIP systems likely result from different case-finding methods, the diagnostic tests used, and the populations monitored.<SUP>?</SUP> Pneumonia- and Influenza-Related Mortality
During the 2006--07 influenza season, the percentage of deaths attributed to pneumonia and influenza (P&I) did not exceed the epidemic threshold** in the 122 Cities Mortality Reporting System (Figure 3). The percentage of P&I deaths peaked three times, once at 7.5% during the week ending January 20, 2007 (week 3), once at 7.7% during the week ending February 24, 2007 (week 8), and again at 7.5% during the week ending March 24, 2007 (week 12). During the previous three influenza seasons, the peak percentage of P&I deaths ranged from 7.8% to 10.4%, and the total number of weeks above the epidemic threshold ranged from one to 16 (1; CDC, unpublished data, 2007). Influenza-Associated Pediatric Mortality
As of August 6, 2007, among persons aged <18 years, a total of 68 deaths associated with influenza infection occurring during October 1, 2006--May 19, 2007, were reported to CDC. These deaths were reported from 26 states (Alabama, Alaska, Arizona, California, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Kansas, Louisiana, Minnesota, North Carolina, Nebraska, Nevada, New Mexico, New York, Ohio, Oklahoma, South Dakota, Tennessee, Texas, Virginia, Washington, and Wisconsin). All patients had laboratory-confirmed influenza virus infection. Age-specific information was available for all 68 persons; 10 were aged <6 months, 10 were aged 6--23 months, nine were aged 2--4 years, and 39 were aged 5--17 years. Of the 63 patients for whom influenza virus type was known, 47 had influenza A and 16 had influenza B viruses. Of the 53 patients aged >6 months for whom vaccination status was known, 50 (94%) had not been vaccinated against influenza. These data are provisional. Worldwide
During the 2006--07 influenza season, influenza A (H1), A (H3), and B viruses cocirculated worldwide. In Africa, small numbers of influenza A and B viruses were reported. In Europe and Asia, influenza A (H3) viruses were identified most frequently, but influenza A (H1) viruses circulated at low levels. Influenza B viruses circulated at lower levels overall in Asia and Europe but predominated in some countries. Human Infections with Avian Influenza A (H5N1) Viruses
From December 1, 2003, through July 25, 2007, a total of 319 human cases of avian influenza A (H5N1) infection were reported to WHO (2). Of these, 192 (60%) were fatal (Table). All cases were reported from Asia (Azerbaijan, Cambodia, China, Indonesia, Iraq, Laos, Thailand, Turkey, and Viet Nam) and Africa (Djibouti, Egypt, and Nigeria). To date, no human case of avian influenza A (H5N1) virus infection has been identified in the United States. <snip>:tiphat: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5631a2.htm