How Effective Does a COVID-19 Vaccine Need to Be?

The “effectiveness” of a vaccine can refer to a constellation of factors: What percentage of vaccinated people develop antibodies? How well do antibodies protect against the disease? How long does this protection last? 

Over the summer, the Food and Drug Administration (FDA) announced that, to receive a regulatory green light, an experimental COVID-19 vaccine must “prevent disease or decrease its severity in at least 50% of people who are vaccinated.”



The FDA has established a threshold for effectiveness that makes it possible for a vaccine to become available that helps only half of the people receiving it while offering no benefit to the other half. It’s also possible that the vaccine may have varying effects—preventing the disease in some while reducing its severity in others. 

A vaccine that’s only 50% effective can still make a difference. For example, flu vaccine effectiveness varies widely from year to year—ranging between 20% and 60% over the last decade. And yet, year after year, flu vaccines reduce illness, hospitalizations, and deaths. 

No vaccine is 100% effective. But some are better than others. Among the most successful is the measles vaccine. According to the Centers for Disease Control and Prevention (CDC), two doses of the measles vaccine is 97% effective in preventing the disease. 

A near-perfect COVID-19 vaccine may not be necessary at all—depending on how many people took it. For example, experts say that if everyone took a 60% effective vaccine, the pandemic could still be tamed via herd immunity. 

Clinical trials assessing the safety and effectiveness of multiple COVID-19 vaccine candidates are currently underway. Through Operation Warp Speed, the government has provided billions of dollars to various biotechnology companies developing vaccines. For example, Moderna has received nearly $2.5 billion to support the development of its vaccine candidate. 

While most trials are evaluating whether a vaccine prevents COVID-19, findings may reveal additional information, such as whether a vaccinated individual that still contracts the virus becomes less sick than someone who hasn’t been vaccinated. 

Study results may also tell us who benefits most from vaccination by comparing men and women, age groups, and people with and without underlying health conditions. Long-term follow-ups are expected to tell us whether vaccines reduce hospitalizations and deaths. 

It’s important to keep in mind that a successful vaccine candidate won’t translate to an immediate end to the pandemic. According to the experts, immunizing millions of people will take time, during which precautions such as face masks, social distancing, and routine hand-washing will remain as crucial as ever. 

What are you doing to keep your organization at the forefront of COVID-19 research and response? Now is a critical time to invest in new skills and training. Get your teams up to speed with professional training and certification courses from the Center for Professional Innovation and Education (CfPIE). 

Are you interested in keeping your organization COVID-ready? Get in touch with a member of the CfPIE team by calling 1-610-648-7550 or emailing [email protected].