The much-awaited swine flu vaccine, currently being developed, will not provide 100 per cent protection against the disease, the World Health Organisation said.

“No vaccines, including pandemic influenza vaccines, provide 100 per cent protection against the disease. But they do greatly reduce the risk of disease,” WHO said in a statement, replying questions related to the vaccine.

According to the WHO, the influenza vaccines will become effective only 14 days after vaccination. Those infected shortly before one to three days or shortly after immunisation can still get the disease.

Moreover, the pandemic influenza vaccines are not expected to provide protection against other influenza virus.

“Since current seasonal influenza vaccines do not contain the pandemic virus, people should be vaccinated against both pandemic influenza and seasonal influenza.”

There are two types of vaccines - one contains killed viruses, which is given by injection into the upper arm for most people. For infants and young children, thigh is the preferred site for the vaccine shot. Another type of vaccine is made with live viruses and it is administered by nasal spray.

Recommendations on number of dosages to be used, is yet to be finalised. While immunisation experts recommend a single dose of vaccine in adults and adolescents from 10 years of age and above, more study is advised on effective dosage regimens for immuno-suppressed persons for whom two doses of vaccine may be needed, the WHO said.