In a White House news conference on Tuesday, Anthony Fauci, the head of the National Institute of Allergy and Infectious Disease, told President Donald Trump a coronavirus vaccine would likely not be available within the next year or two. Trump responded: “I like the sound of a couple of months better.”

But a vaccine is not going to be available in the next couple of months, and according to Dr. Paul Offit, that’s appropriate. Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, is the co-developer of the rotavirus vaccine. It took roughly 26 years to perfect that protection against a disease that, according to the CDC, was the leading cause for severe diarrhea in children prior to the vaccine’s introduction in 2006.

Offit talked to the Philadelphia Inquirer about the process of vaccine development, the risks of rushing, and the role of vaccination amid the coronavirus outbreak.

Responses have been edited for length and clarity.

Question: Why is it unrealistic to expect a vaccine for coronavirus in a few months?

Answer: Nobody’s ever seen this virus before. Therefore, if you’re interested in making a vaccine, you first had access to that virus only a couple months ago. That’s not long.

(To make a vaccine) you first need to make a decision as to what approach you want to take. Then you have to do extensive animal model testing to make sure that the approach that you’ve taken is safe in animals, and that it induces an immune response which would likely be protective. Then you gradually do studies in people to make sure it’s safe, and then to make sure that it induces an immune response. That takes time, a lot of time, typically years. Then and only then, are you ready to put it into people to see whether or not it works in an outbreak situation.

Q: In 2018, after the World Health Organization declared an Ebola outbreak in the Democratic Republic of Congo, there was an experimental vaccine very quickly.

A: I think people got fooled by Ebola. When the outbreak occurred in West Africa and we had a vaccine pretty much that rolled off shelf within weeks, people thought, Ha! That’s easy.

But what they didn’t realize is people have been working on an Ebola vaccine for 20 years. They’ve done the animal model testing. They’ve done the testing to make sure that the vaccine was safe and was immunogenic.

But that’s not true here. This is a new virus. So we’re starting from scratch.

Q: What is it about this virus that makes people confident that a vaccine will be available?

A: I don’t know. You know, I’d say about 15% to 20% of the respiratory infections that we see in our hospital in the winter months are (types of) coronavirus. This is a virus that has been around for 50 years.

But here are these three newer strains of coronavirus — MERS, SARS and now this COVID-19. The first two viruses, SARS and MERS, have come and gone.

I think this (COVID-19) virus likely will come back because it’s different. If you were infected with SARS or MERS viruses, you were sick. And it’s very easy to tell who was sick and who wasn’t. You could then quarantine those people — put a moat around them, if you will — so that they wouldn’t infect others. So those infections quickly died out. This virus is more like flu. It spreads in a similar manner to flu by respiratory droplet. It’s about as contagious as flu. It has the same set of symptoms as flu. And I think in the end, frankly, it’s going to have the same mortality rate as flu.

There are certainly human studies showing that if you’re infected with a coronavirus — meaning one of the typical coronaviruses — you can have immunity to that strain for at least a year and probably longer. That’s encouraging. If natural infection can protect you, then it’s encouraging that it can produce an immune response which is protective and which you should be able to mimic with vaccination.

Q: Vaccine development is tightly regulated. How much that is about safety vs. red tape?

A: If you’re going to be testing this in otherwise healthy people who are very, very unlikely to die from this infection, you better make sure it’s safe. So you want those regulations in place.

An example is the dengue vaccine. When it was tested in Latin America and Philippines, it was found to actually increase your risk of dengue shock syndrome. Children who were less than 9 years of age, who had never been exposed to the virus before, were actually more likely to be hurt by the vaccine than helped by it. Now, you only knew that from doing large clinical trials with tens of thousands of people.

The history of medical breakthroughs is littered with tragedy. You want to make sure that things are safe.

Q: What do you think is behind the rush?

A: I think that because we falsely overrate, or incorrectly rate, what the mortality rate is, we’re willing to accept that things will be rushed through. In fact, coronavirus doesn’t have a high mortality rate.

There’s a virus that the CDC currently estimated has killed between 20,000 and 45,000 people in the United States — influenza. But only half the country gets that vaccine.

There’s only 14 deaths (in the U.S., as of Friday afternoon) from COVID-19, but everybody would get a vaccine now.

The point being: We’re not very good at assessing risk.