FDA recently approved two new vaccines manufactured by Merck and Co. The first one, called Gardasil, prevents cervical cancer, precancerous genital lesions and genital warts caused by human papillomavirus (HPV).

Gardasil is effective against four types of HPV: types 16 and 18, which cause about 70% of cervical cancers, and types 6 and 11, which cause about 90% of genital warts. Gardasil is approved for use in girls and women aged 9 to 26. Merck is currently studying the safety and effectiveness of the vaccine in males.

In clinical studies conducted in 21,000 women, Gardasil was nearly 100% effective in preventing HPV disease for the four virus types covered by the vaccine. Of course, the vaccine won't protect a woman against a type of HPV that isn't in the vaccine, and it won't work as a treatment against HPV. For those reasons, and because no vaccine is 100 % effective, routine Pap screening is still recommended.

Merck's other vaccine, called Zostavax, is used to reduce the risk of shingles in people 60 and older.

Shingles is caused by a reactivation of the varicella zoster, or chickenpox, virus. It can occur at any age, but it is most common in people over 60, and the risk increases as people get older.

In clinical studies conducted in approximately 38,000 people, the vaccine reduced the overall occurrence of shingles by about 50%. The vaccine's effectiveness was 64% in people between the ages 60-69, but it declined with increasing age to 41% for those in their 70's, and 18% for those 80 and older.

Zostavax should not be used in people who are allergic to neomycin or any component of the vaccine. And since Zostavax is a live attenuated vaccine, it should not be given to people who have weakened immune systems or to women who are or may be pregnant. Zostavax should also not be used in children and it is not a substitute for Varivax, the vaccine used to prevent chicken pox.