Younger children will need two doses of the new swine flu vaccine, but clinical trials suggest the drug is working well, health officials said Monday.

    "Immunologically this is acting like seasonal flu and we are very pleased with that," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. "The response in younger children is less robust, but that is not unexpected."

    A single 15 microgram dose of swine flu vaccine is enough for kids 10 and older, while children under 10 will need two doses, 21 days apart.

    Younger kids need the double dose because their immune systems are not fully mature, Fauci said.

    Officials called the trial results "encouraging" given that three quarters of healthy kids over 10 developed an immunity to the virus.

    "Overall, this is very good news for the vaccination program," Fauci said. "76 percent is not bad at all - it's quite good I think."

    One dose was about half as effective in kids nine and younger, Fauci said, but the second dose will boost their immunity substantially.

    Kids in the clinical trial reported only minor side effects that are typical of the seasonal flu vaccine, such as soreness in the arm after a shot, Fauci said

    Some 47 children have died of swine flu since it first emerged in the spring. Unlike seasonal flu, which tends to be worst among the elderly, swine flu hits kids hardest.

    The officials recommend children and adults get the seasonal flu vaccine ahead of the swine flu vaccine to prevent logistical problems with separating the doses.

    The first of swine flu vaccine will be nasal sprays, not shots, meaning many at-risk groups will have to wait for the injectable vaccine to be released in late October.

    The city Department of Health, which will offer free vaccines to all school aged children this fall, says the spray and shot are equally effective among healthy people ages 2 to 49.

    健康官員們在周一說，年幼的孩子們將需要兩個劑量新的豬流感疫苗，而臨床試驗顯示這種藥物正在很好地起作用。

    "從免疫學上看，這樣的行為象季節性流感，并且我們對此很滿意，"美國國家過敏癥和傳染病協會的主任安東尼 福奇博士說。"在年幼的孩子中的反應不太穩健，但是那并不意外。"

    對于 10 歲和 10 歲以上的孩子們，單個 15 微克劑量的豬流感疫苗就足夠了，而 10 歲以下的孩子們將需要二個劑量，間隔 21 天。

    年幼的孩子們需要雙倍劑量，因為他們的免疫系統沒有完全成熟，福奇說。

    官員們稱試驗的結果"令人鼓舞",已知四分之三 10 歲以上的健康孩子對這種病毒發生了免疫力。

    "總的來說，這對疫苗接種計劃來說是非常好的消息，"福奇說。"76% 一點也不差--我覺得它很不錯。"

    一個劑量大約是九歲和九歲以下孩子們的有效劑量的一半，福奇說，但是第二劑量會顯著地增強他們的免疫力。

    臨床試驗的孩子們只報告有輕微的副作用，是季節性流感疫苗的典型特征，例如注射后的手臂酸痛，福奇說

    自從豬流感在春天首次出現以來，大約 47 名兒童死于豬流感。不像季節性流感，往往是稍年長者情況最差，豬流感打擊孩子最嚴重。

    官員們推薦的兒童和成人在豬流感疫苗之前接種季節性流感疫苗，采取分開的劑量防止后勤供應問題。

    第一劑豬流感疫苗將是鼻腔噴霧劑而不注射，意味著許多處于風險的群組將不得不等待 10 月下旬發放的注射疫苗。

    城市衛生部門--他們今年秋天將對所有學校年齡的孩子們提供免費疫苗--說，在年齡 2 至 49 歲的健康人中，噴霧和注射是同樣有效的。