Why is it so hard to find a vaccine for COVID-19?

There are more than 40 COVID-19 vaccines in development, but it will probably be at least 12 to 18 months before a safe, effective vaccine is available. The time-consuming part of making a vaccine is showing that it is safe and actually prevents people from getting COVID-19. Making sure the vaccine is safe is important because lots of healthy people will get the vaccine, so if it doesn’t work or even a few people got sick from it, that would be a big deal.

Here’s how doctors go about showing a vaccine works and is safe. First, they test it on animals to show that giving the vaccine causes the animals to make protective proteins called antibodies, which our bodies use to fight the virus that causes COVID-19. 

Then, doctors move on to human testing. Doctors recruit small numbers of volunteers to make sure that the vaccine is safe for humans and that it also causes humans to make protective antibodies. This is called a Phase I clinical trial.

Next, doctors move on to larger trials, called Phase II and Phase III trials. In these trials, doctors give the vaccine to more people to make sure it prevents them from getting sick with COVID-19. Each of these trials can take months to complete, even under ideal circumstances, because people’s bodies take a few weeks to produce antibodies after they get vaccinated. And after that, it takes even more time to confirm that the vaccine actually keeps people from getting sick. The whole time, doctors carefully monitor all the people in the studies for bad reactions to the vaccine.

Vaccines are one of the safest and most effective public health interventions available, in large part because doctors are so careful about making them. It’s hard to be patient when facing a crisis, but it’s important to make sure we get it right!

Last Updated: April 7, 2020 11:05 am ET

Science review by: GSN, ERS, JAB