One dose of the vaccine against pandemic H1N1 influenza should be enough for everyone except children under the age of 10, and the vaccine is proving to be safe, the World Health Organization said this morning. Dr. Marie-Paule Kieny, the agency's vaccines chief, told a telephone news conference that data from clinical trials that have already been conducted indicate that one dose of vaccine is sufficient to provoke a strong immune response against the swine flu virus. The United States and some other countries have already concluded that one dose is sufficient, but others have questioned the conclusion. The European Medicines Agency said last week that the swine flu vaccines it had licensed should be given in two doses at least three weeks apart because the current data were "too limited" to allow it to recommend only one dose.
Experts had initially feared that two doses of the vaccine would be required for everyone because preliminary experiments hinted that the virus did not provoke a strong immune reaction. The conclusion that only one dose is necessary effectively doubles the amount of vaccine available -- a crucial result for those developing countries which are having problems obtaining the vaccines. The WHO said earlier this week that it would begin distributing 200 million doses to such countries.
The sole exception to the new recommendation is young children, who should continue to receive two doses. That recommendation is not surprising, because a similar requirement is in place for seasonal flu shots. Researchers have found in the past that some residual immunity from previous vaccinations boosts the body's response to a flu vaccine, which is why adults need only one dose. But children who have not previously been exposed to a flu vaccine need two shots to get the proper protection.
Kieny also said that the new swine flu vaccine appears to be safe, as authorities have been saying all along. "All the reports received to date following vaccination -- either in clinical trials or in mass vaccination campaigns -- have shown that the safety profile of these pandemic vaccines is good and is very similar to the one which is known for seasonal flu vaccine," she said. "Nothing special in terms of adverse events has been noted."
Kieny said that it was safe to vaccinate against both seasonal and swine flu simultaneously, as long as at least one of the vaccines is the injectable form. That follows U.S. guidelines, which say that two doses of the intranasal FluMist vaccines should not be given at the same time.
In other flu news:
-- At a Philadelphia meeting of the Infectious Diseases Society of America, officials of the group strengthened their recommendation that shots against both types of flu should be mandatory for healthcare workers and that unvaccinated doctors and nurses should either wear masks or not deal with patients. "All of us and all our colleagues who work in direct patient care should be immunized," said Dr. Ann Gershon of the Columbia University Medical Center, the group's president. "We owe it to our patients." The group said voluntary educational programs have failed to raise the vaccination rate above 70%, putting patients at risk.
-- Intravenous antiviral drugs are proving useful in severe illness caused by swine flu infections, experts told physicians Thursday in a conference call for physicians sponsored by the Centers for Disease Control and Prevention. The Food and Drug Administration last week approved emergency use of the intravenous antiviral peramivir and a related drug, zanamivir, even though clinical trials of the drugs have not been completed. Dr. Stacene Maroushek, an infectious-disease specialist at Hennepin County Medical Center in Minneapolis, described the case of a 17-year-old boy who became sick at the Minnesota State Fair and who was failing rapidly and was expected to die, even though he was receiving Tamiflu through a nasogastric tube. Physicians gave him IV peramivir for five days, and he began improving on the second day of treatment. Although he is still weak, he is improving with therapy and rehabilitation and is now at home, she said. The 25-day hospitalization cost about $300,000.
Dr. Aditya Gaur of St. Jude's Children's Research Hospital in Memphis described the case of a 10-year-old girl who was immunocompromised because she was undergoing treatment for leukemia. She was initially treated with Tamiflu and discharged, but 12 days later was rehospitalized with pneumonia. Tests showed her strain of the swine flu was resistant to Tamiflu. She was given IV zanamivir and her symptoms have improved substantially, Gaur said. Experts said that it is crucial that the IV drugs be continued for at least 10 days to make sure the virus is eradicated.
-- Thomas H. Maugh II