There’s no need to worry on the safety or efficacy of the anti-swine flu vaccines being currently developed in different countries, said the World Health Organization.

Taking notice of the fears being expressed in different quarters on the safety or risks in using the vaccines, the WHO said the regulatory procedures in place for the licencing of pandemic vaccines, including procedures for expediting regulatory approval, are rigorous and do not compromise safety or quality.

Drug companies in several countries are in an advanced stage of developing a H1N1 influenza vaccine to check the swine flu pandemic which has swept across over 160 countries, affecting over 1.5 million (confirmed cases; actual number may be far higher) and killing nearly 1,000 persons. In India, too, over two dozen people have lost their lives due to swine flu in recent weeks, in different cities.

Some Indian drug companies are also engaged in developing a swine flu vaccine based on the seed strain of H1N1 influenza virus provided by the WHO. However, it may take a few months to develop and test the vaccines and get approval for their general use.

In a statement issued from Geneva, the WHO has said: "Influenza vaccines have been used for over 60 years and have an established record of safety in all age groups." At the same time, it has also cautioned that some adverse events may arise during a pandemic when the vaccine is administered on a massive scale.

"Some adverse events, which may be too rare to show up even in large clinic trials, may become apparent when very large numbers of people receive a pandemic vaccine," the WHO has said, while maintaining that such cases will be rare.