DENVER (KDVR) — Two companies claim to have a vaccine for COVID-19, and initial reports put the effectiveness on par with other largely eradicated diseases.

Drug maker Moderna said Monday its vaccine is 94.5% effective, just a week after Pfizer Inc. made a similar claim.

They will likely seek emergency distribution.

Vaccines began in the late 18th century with smallpox. Through the next two centuries, technology and knowledge advanced in the medical field. The U.S. Food and Drug Administration now licenses nearly 100 vaccines for 26 infectious diseases.

The U.S. Centers for Disease Control and Prevention uses two metrics for a vaccine’s effectiveness in preventing disease infection, hospitalization and death: vaccine efficacy and vaccine effectiveness.

Vaccine efficacy involves a lab-controlled setting that tests under ideal circumstances, while vaccine effectiveness measures the vaccine’s success in field conditions – necessary for a pandemic already far underway. Efficacy is the best case scenario, effectiveness the worst.

Flu vaccines vary in effectiveness widely across age groups and years due to the many influenza strains circulating in the population at a given time.

As a specific strain, COVID-19 bears more similarity to other diseases with available vaccines.

At 94.5%, Moderna’s vaccine would make a COVID-19 vaccination nearly as effective as vaccines for rubella, polio and measles, each of which has been swept from former positions as public health menaces in the 19th and 20th centuries.