Division of Disease Control and Health Protection

1. FDA Approves Tamiflu for Prevention

2. Influenza and RSV Update

3. Polio Outbreak in Haiti and the Dominican Republic

4. Weekly Disease Table: Week 47

November 20, 2000—FDA today approved another indication for Tamiflu (oseltamivir phosphate), a neuraminidase inhibitor. Its new additional indication is for prevention of influenza in adults and children 13 years and older. Tamiflu is an oral anti-viral drug previously approved by FDA for the treatment of uncomplicated influenza in adults.

In a pooled analysis of two seasonal prophylaxis studies in healthy unvaccinated adults and adolescents, Tamilflu 75 mg once daily taken for 42 days during a community outbreak reduced the incidence of laboratory confirmed clinical influenza from 4.8 percent for the placebo group to 1.2 percent for the Tamiflu group. In a seasonal prevention study in elderly residents of nursing homes, 75 mg of Tamiflu taken once a day for 42 days reduced the incidence from 4.4 percent for the placebo group to 0.4 percent for the Tamiflu group. Approximately 80 percent of this elderly population were vaccinated against the influenza.

In a study of post-exposure prevention in households, 75 mg of Tamiflu was given once daily within two days of onset of symptoms and continued for seven days. Results of this study show Tamiflu reduced the incidence of laboratory confirmed clinical influenza from 12 percent in the placebo group to 1 percent in the Tamiflu group.

Side effects from Tamiflu, when taken for prevention, were similar to those from patients who took the drug for treatment. The most common side effects were nausea, vomiting, headache and fatigue.

Efficacy for Tamiflu for the prevention of influenza has not been established in immunocompromised patients.

Patients should continue receiving an annual flu vaccination according to the guidelines on immunization practices. Tamiflu is not a substitute for the flu vaccine.

Tamiflu is manufactured by Roche Pharmaceuticals, Inc. of Nutley New Jersey and Gilead Sciences, Inc. in Foster City C.A.

National report: During week 45 (November 12-18, 2000), 583 specimens were tested by World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories across the United States. Eighteen isolates, 16 influenza A (H1N1), one influenza A(H3N2) and one influenza B virus. Since October 1, 77 (1%) influenza isolates (57 influenza A (H1N1), 5 influenza A (H3N2) and 8 influenza B) have been recovered from 6,763 specimens tested. Influenza A(H1N1) have been identified from California, Colorado, Florida and Texas; influenza A(H3N2) isolates have been identified in Florida, Hawaii and Kentucky and influenza B isolates have been identified in Alaska, California, Florida and Oklahoma.

The percentage of all deaths due to Pneumonia and Influenza (P&I) as reported by the vital statistics offices of 122 U.S. cities was 6.6% during week 46. This percentage is below the epidemic threshold of 7.8% for this time of year.

Regional influenza activity was reported from state and territorial health departments in Kentucky and Texas. Sixteen states (Alabama, Alaska, Arkansas, Colorado, Florida, Georgia, Hawaii, Indiana, Kansas, Louisiana, Maine, Michigan, New Mexico, Ohio, Oklahoma and Tennessee) reported sporadic influenza activity. No influenza activity was reported from twenty-four states.

During week 46, 1% of patient visits to U.S. sentinel physicians were due to influenza-like illness (ILI). The percentage of ILI was within baseline levels of 0% to 3% in all 9 surveillance regions.

Florida: Data from Florida suggest low levels of influenza activity. Overall, two percent of 13, 028 patients seeking care by reporting physicians in the influenza sentinel surveillance system met the case definition for ILI during week 46. Influenza-like illness activity was detected in 13 counties from Leon to Miami Dade. Higher flu activity than expected for this time of year (>3%) was reported by physicians in Leon and Polk counties. No new influenza virus isolates were recovered this week. This far 17 isolations have been made at the state labs this season.

Respiratory syncytial virus (RSV) activity appears to be higher in north Florida than in the southern part of the state. Eleven hospital laboratories in the state reported that 23.1-50% of RSV tests performed were positive. This is an increase from week 44 when the percentage of positive tests ranged from 25-42.5%. The highest percentage was reported from north east Florida, the lowest from the southwest.

Washington, December 1, 2000 -- A current outbreak of poliomyelitis in Dominican Republic and Haiti has raised serious concerns because the Western Hemisphere has been free of wild poliovirus circulation since 1991, and because the virus identified is an unusual derivative of the Sabin type 1 oral poliovirus vaccine (OPV), according to Dr. Ciro de Quadros, who directs the Pan American Health Organization’s Division of Vaccines and Immunization.

The Ministries of Health of the Dominican Republic and Haiti, with the assistance of the Pan American Health Organization (PAHO) and the Centers for Disease Control and Prevention (CDC), are investigating the outbreak to determine the extent of spread and evaluate the reasons for the outbreak. Aggressive control measures have already been put in place. A mass vaccination campaign with OPV has already started in the Dominican Republic, initially covering the three provinces with suspected cases, followed shortly by the rest of the country. In Haiti, three nationwide vaccination rounds with OPV are planned for January, February and March.

Since July 12, 2000, a total of 3 laboratory-confirmed cases due to derived poliovirus type 1 isolates have been identified, Dr. de Quadros said. An additional 16 persons with acute flaccid paralysis (AFP) are now under investigation in the Dominican Republic. In Haiti, a single laboratory-confirmed case due to the derived type 1 virus has been reported to date, with paralysis onset on August 30. After intensive case-finding activities, no other cases have been found so far. The virus detected, first isolated by the PAHO Poliovirus Laboratory at the Caribbean Epidemiology Center and subsequently characterized at the Poliovirus Laboratory at the Centers for Disease Control and Prevention (CDC) is unusual because it is derived from OPV, has 97 percent genetic similarity to the parental OPV strain (normally OPV derived viruses are greater than 9.5 percent), and appears to have assumed the characteristics of wild poliovirus type 1, both in terms of neurovirulence and transmissibility. The difference in nucleotide sequence suggests the virus has been either replicating for a prolonged period in an immunodeficient individual, or circulating for as long as two years in an area where vaccination coverage is very low, resulting in ongoing genetic changes in the original Sabin virus that gave it the properties of wild poliovirus.

Prolonged circulation of OPV-derived polioviruses in areas with very low OPV coverage has been documented in only one other setting--type 2 OPV-derived virus circulated in Egypt for an estimated 10 years (1983-1993) and was associated with more than 30 reported cases. In this instance, vaccination coverage was very low in the affected areas, and circulation of a vaccine-derived poliovirus was terminated rapidly once OPV vaccination coverage increased.

The key factor for control of circulating OPV-derived viruses is the same as that required to control wild poliovirus circulation: achieving and maintaining high vaccination coverage, Dr. de Quadros said No evidence for circulation of OPV-derived virus has ever been found in any area with high coverage.

"The current outbreak is a powerful reminder that even polio-free areas need to maintain high coverage with polio vaccine until polio eradication has been achieved," Dr. de Quadros said.

"Nearly four decades of experience with oral polio vaccine has shown that it is very safe and effective in preventing poliomyelitis. OPV is the vaccine of choice for the eradication of wild polioviruses. However, it is crucial to maintain high OPV coverage to protect against imported wild polioviruses and to prevent person-to-person transmission of OPV-derived viruses," he added.

"It is also important that all countries maintain high quality AFP and poliovirus surveillance, that current activities to complete the global eradication of wild polioviruses be accelerated, and that a global strategy is developed for the orderly cessation of immunization with OPV after global certification of polio eradication is achieved,"Dr. de Quadros said.

Travelers to the Dominican Republic and Haiti who are not adequately immunized must be considered at risk of acquiring poliomyelitis, and should make certain they are fully immunized against polio. Those countries using OPV for routine immunization recommend at least a 3-dose primary vaccination series.

PAHO, which also serves as the Regional Office for the Americas of the World Health Organization, works to improve health and raise living standards in all the countries of the Americas.

For further information, contact: Daniel Epstein, Pan American Health Organization, Office of Public Information.