Two key late-stage studies of Pfizer's blockbuster pneumococcal vaccine for children show it works at least as well as a rival in adults, a big market the drugmaker wants to tap.
The studies of Pfizer Inc.'s Prevnar 13 vaccine against pneumonia, meningitis and other infections were presented Monday at two medical conferences in Milan, Italy. The results have been submitted to regulators in the U.S., European Union and more than a dozen other countries where New York-based Pfizer is seeking approval for people over 49.
It said the studies show the shots worked as well as or better than an older pneumococcal vaccine made by Merck & Co, Pneumovax 23.
Prevnar, developed by Pfizer unit Wyeth, is the world's top-selling vaccine, with 2010 sales of about $3.7 billion.
Pfizer hopes to boost that significantly to offset increasing generic competition for other products. Its cholesterol fighter Lipitor, the world's best-selling medicine, loses U.S. patent protection on Nov. 30 and its $11 billion in annual sales will quickly plunge. Several smaller sellers have gotten generic competition recently, eroding revenue.
Prevnar 13, launched early last year for children aged six weeks through five years old, protects against 13 strains of pneumococcal disease, compared with seven for the original version. Merck's shot protects against 23 strains, 12 of them covered by Prevnar 13.
The two new studies are among six that tested about 6,000 adults aged 50 years and older.
One found Pfizer's shot induced a stronger antibody response then Merck's vaccine for most pneumococcal strains that both vaccines target.
The second study, of patients aged 70 years or older, found those who received two Prevnar shots a year apart had a stronger antibody response than participants who first got the Merck shot and then got the Pfizer vaccine a year later.
Vaccines induce the immune system to make antibodies against bacteria or viruses so the body can mount a quick defense against any future infection.
In both studies, the Pfizer and Merck vaccines produced similar side effects, mostly swelling and redness where injected.
Merck's Pneumovax 23 is recommended for people 65 and older and for younger patients with weak immune systems. Like many other vaccines for adults, it's not that widely used; 2010 sales totaled only $376 million.
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 shots adults should get, but for children it's four shots between 2 and 15 months.