- Associated Press - Monday, November 14, 2011

WASHINGTON (AP) - Federal health scientists say Pfizer’s best-selling vaccine, Prevnar 13, is at least as effective as rival Merck’s at helping prevent sometimes deadly infections in adults.

Prevnar 13 is intended to reduce the risk of infection by 13 strains of pneumococcal disease, which causes ear infections, meningitis and pneumonia. Vaccination with Prevnar is recommended for all U.S. infants and young children, because of their vulnerability to infection. But the disease also affects 36,000 older adults per year, killing 5,000 of them, according to the latest figures from the Centers for Disease Control and Prevention.

Pfizer, which is based in New York, has asked the FDA to expand Prevnar’s approval for adults 50 and older.

In a review posted online Monday, FDA scientists said Prevnar triggered an immune system response comparable to Merck’s Pneumovax, the only vaccine currently approved for adults. Vaccines strengthen the body’s immune system by spurring production of antibodies against bacteria or viruses. In six studies of more than 6,000 adult patients, Prevnar generated at least as many antibodies against pneumococcal disease as Pneumovax.

Side effects were comparable for the two vaccines, including swelling and redness at the injection site as well as fever, chills and fatigue.

On Wednesday the FDA will ask a panel of outside experts whether Prevnar appears safe and effective for adults. The group’s recommendation is not binding, but the agency often follows its guidance.

The CDC currently recommends vaccination for all adults 65 or older with Merck’s Pneumovax, which protects against 23 strains of pneumococcal disease, including 12 that overlap with Prevnar. Only about two-thirds of eligible seniors get the injection.

But Merck’s vaccine has not been shown to protect against pneumococcal pneumonia, one of the most dangerous infections associated with the disease. The FDA agreed to give Prevnar an accelerated review, based on currently available studies, because of its potential to defend against pneumonia. Pfizer is still conducting an 85,000-patient study in the Netherlands to assess Prevnar’s strength against pneumonia in adults. The company must submit the results to the FDA after the study concludes, which is expected in the next two years.

Merck’s Pneumovax is only approved for children older than 2 and adults over 50 who are at increased risk for pneumococcal disease. Sales last year totaled $376 million. Prevnar, approved for babies as young as six weeks old, was the top-selling vaccine in the world last year, with sales of about $3.7 billion.

Pneumovax sells for about $50 a shot on average, while Prevnar 13 costs $114 on average. Adults need one or two Pneumovax shots and then a booster after age 65. Pfizer hasn’t determined how many Prevnar boosters will be needed after the initial dose.

Because Merck’s vaccine protects against strains not covered by Prevnar, it is likely seniors would receive both.

Pneumovax was first approved in 1977 and uses an older vaccine mechanism than Prevnar, which was first approved in 2000. Prevnar is a conjugated vaccine, which means it contains pneumococcal bacteria connected to a protein. The addition of the protein helps the immune system recognize the bacteria, especially in babies.

Shares of Pfizer Inc. fell 23 cents to $19.76 in trading. Shares of Whitehouse Station, N.J.-based Merck & Co. Inc. fell 40 cents to $35.57.

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