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Swine Flu Outbreak May Be on the Wane: CDC

FRIDAY May 22, 2009 -- While many states are still reporting new cases of infection with the H1N1 swine flu virus, there seems to be an overall decline in visits to doctors and hospitals by people with the disease, indicating that the outbreak might be subsiding, a U.S. health official said Thursday.

"At the national level, we're seeing that the percent of visits [to doctors and hospitals] for influenza-like illness is starting to turn down," Dr. Anne Schuchat, the Centers for Disease Control and Prevention's interim deputy director for science and public health program, said during an afternoon teleconference. "That's a good sign. It's consistent with the idea that the worst may be over."

"We are seeing activity decline in some areas, but we are seeing increased or localized outbreaks in other areas," she added.

Schuchat also discussed the finding, first reported Wednesday, that some older people may have partial immunity to the new H1N1 swine flu virus because of possible exposure to another H1N1 flu strain circulating prior to 1957.

The finding "suggests that older adults might have some preexisting antibody against this new H1N1 strain," Schuchat said. "But we don't know yet what that will mean in terms of actual immunity or clinical protection."

So far, 64 percent of cases of swine flu infection are among people aged 5 to 24, while only 1 percent involves people over 65, she said.

On Wednesday, Dr. Daniel Jernigan, deputy director of the CDC's Influenza Division, said that some older people may have partial immunity to the new H1N1 swine flu virus because of possible exposure to another H1N1 flu strain circulating prior to 1957.

"The further back you go in time, the more likely you are to have been exposed to H1N1 virus back before 1957, and there is a possibility that having exposure to that virus many years ago may allow you to have some [antibody] reaction to the new H1N1 that's now circulating," he said.

That could explain why the new swine flu outbreak is striking a disproportionately large number of children and young adults. The regular seasonal flu typically takes the biggest toll among the very young and the elderly.

The current H1N1 virus is a genetic cousin of the more virulent H1N1 "Spanish flu" virus of 1918 that killed 20 million to 50 million people worldwide, and up to 500,000 in the United states. Seasonal versions of this virus circulated throughout the United States until it was replaced in 1957 by the H2N2 "Asian flu" pandemic virus, which caused 70,000 deaths in the United States, according to the U.S. National Institute of Allergy and Infectious Diseases.

Jernigan said studies have found evidence of H1N1 antibody activity in blood from older people. "We can infer from that, to some degree, that there is some level of protection," he said.

But he added a note of caution, saying that many years have passed and the new virus, although the same subtype, is different from the H1N1 seasonal flu virus circulating before 1957.

Jernigan also said that in the United States, the steps needed to produce a swine flu vaccine are moving ahead on schedule, and a vaccine should be ready by the fall. "We are moving along and have not had significant delays here in the U.S. with the development of the vaccine candidates," he said.

He also suggested the possibility of making the regular seasonal flu vaccine available earlier to Americans than its usual late September or early October introduction this year, to be followed by a second vaccine for swine flu, if needed.

"At this point when to vaccinate [with the new H1N1 vaccine] is going to be driven largely by when it's available," Jernigan said. "If possible we want to have an earlier roll-out of the seasonal influenza vaccine, to make it easier for an additional vaccine if that's the ultimate policy," he said.

In the United States, most cases of swine flu continue to be no worse than seasonal flu, health officials said. Testing has also found that the swine flu virus remains susceptible to two common antiviral drugs, Tamiflu and Relenza, according to the CDC.

The new swine flu is a highly unusual mix of swine, bird and human flu viruses. Experts worry that, if the new flu virus mutates, people would have limited immunity to fight the infection. The CDC is concerned that, as the H1N1 virus moves into the Southern Hemisphere, where the flu season is about to start, it could mutate and return in a more virulent form in the Northern Hemisphere next fall.

On Thursday, the CDC was reporting 5,764 U.S. cases of swine flu in 48 states, including nine deaths, although health officials said the death toll could be as high as 10.

The World Health Organization on Friday was reporting 11,168 diagnosed cases in 42 countries, including 86 deaths, mostly in Mexico, believed to be the source of the outbreak.

Mexico City on Thursday lowered its swine flu alert level from yellow to green after no new infections had been reported for a week, the Associated Press reported.

U.S. Human Cases of H1N1 Flu Infection
(As of May 21, 2009, 11:00 AM ET)
States # of
confirmed and
probable cases
Deaths
Alabama
64
1 deaths
Arkansas
3
 
Arizona
488
2 deaths
California
553
 
Colorado
55
 
Connecticut
59
 
Delaware
88
 
Florida
122
 
Georgia
25
 
Hawaii
30
 
Idaho
8
 
Illinois
794
 
Indiana
105
 
Iowa
71
 
Kansas
34
 
Kentucky**
20
 
Louisiana
73
 
Maine
9
 
Maryland
39
 
Massachusetts
175
 
Michigan
171
 
Minnesota
39
 
Mississippi
5
 
Missouri
20
1 deaths
Montana
9
 
Nebraska
28
 
Nevada
33
 
New Hampshire
22
 
New Jersey
22
 
New Mexico
68
 
New York
284
1 deaths
North Carolina
12
 
North Dakota
5
 
Ohio
13
 
Oklahoma
43
 
Oregon
94
 
Pennsylvania
61
 
Rhode Island
8
 
South Carolina
36
 
South Dakota
4
 
Tennessee
86
 
Texas
556
3 deaths
Utah
116
1 deaths
Vermont
1
 
Virginia
23
 
Washington
411
1 death
Washington, D.C.
13
 
Wisconsin
766
 
TOTAL*(48)
5,764 cases
9 deaths
*includes the District of Columbia
**One case is resident of Ky. but hospitalized in Ga.Source: U.S. Centers for Disease Control and Prevention

More information

For more on swine flu, visit the U.S. Centers for Disease Control and Prevention.

Posted: May 2009


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