A vaccine against RSV has proven elusive despite decades of attempts. Pfizer is moving at a surprisingly quick pace to catch up to rivals led by GlaxoSmithKline, who have finally begun showing progress on an inoculation. GSK began a 25,000-patient study in May that’s due to yield primary results in May 2022. Pfizer says its trial may conclude as early as the first quarter of 2022.

Johnson & Johnson is not far behind. The company began a 23,000-patient study of its RSV shot in July and expects primary results by June 2023. Like GSK and Pfizer, its vaccine focuses on a viral protein called F that RSV uses to attack human cells. Moderna, meanwhile, is in earlier testing of an inoculation using mRNA technology similar to its COVID-19 vaccine.

While most people who become infected with RSV experience only cold-like symptoms, the virus can be deadly for certain populations. Under normal conditions, RSV causes about 177,000 hospitalizations and 14,000 deaths a year among adults 65 and over, according to the Centers for Disease Control and Prevention.

Infants are also vulnerable to severe infections. The CDC estimates that RSV leads to about 2.1 million outpatient visits and 58,000 hospitalizations every year for patients under 5 years old.

A successful vaccine could generate billions of dollars in sales, according to analysts at Cowen, who predict a total market worth nearly $10 billion by 2028.