The new coronavirus vaccine may be the key to ending the pandemic. It joins a list of vaccines that over time have prevented serious illness and even death in the United States.

As demand surges for the COVID-19 vaccine, the spotlight now turns to understanding how vaccines, in fact, work.

Kate Langwig, a quantitative disease ecologist and an assistant professor in the Department of Biological Sciences at Virginia Tech, breaks down the basics about vaccines, why they are important, and how they have protected mankind for decades.

Q. Why are vaccines important?

Langwig: Vaccines are one of the most important ways to succeed in eradicating or controlling any infectious diseases. One of the reasons that humans today have fairly long average lifespans is because of vaccines. Vaccines have been this amazing scientific marvel, the best health care advance that we can even imagine over the last century that has allowed us to combat diseases that were lethal.

Q. What vaccines have been the most effective over time?

Langwig: Smallpox is the only human disease to date that we have actually eradicated. That is in part because of the very high efficacy of the vaccine. Smallpox was responsible for some of the largest scale disease-caused human mortality events throughout history. We were able to eradicate it through vaccines. Also, polio, which can cause debilitating paralysis, has been eradicated in the U.S. and most of the rest of the world because of vaccines. They are absolutely critical to maintaining our health infrastructure.

Loading player for https://video.vt.edu/media/1_1nk43fyl...

Q. What does it mean for a vaccine to be effective? What should it do?

Langwig: Most of the time we expect that vaccines are transmission blocking, although for most studies, vaccines need to be more than 50 percent effective in preventing symptoms of disease. Transmission blocking vaccines protect individuals against becoming infected in the first place. 

The COVID-19 vaccines currently licensed in the U.S. are more than 90 percent effective in preventing symptoms of the coronavirus in trials. We just don’t know whether they block transmission yet.

Q. What has been most challenging about getting the message out to the public that having the coronavirus vaccine is important?

Langwig: One of the core issues that we’ve been dealing with in terms of vaccines in the last decade or so has been vaccine hesitancy. People have become more skeptical of vaccines and part of that is because we do such a good job of controlling a lot of these diseases. The public health impact of these diseases is no longer at the forefront of our consciousness.

I think that COVID-19 might affect vaccine hesitancy. By the end of this, I don’t know that there will be anyone left in this country who has not been touched by COVID in some way. I wonder if that will result in sort of a renewed faith and a renewed enthusiasm for vaccinations.

Q. What is herd immunity and why is it important?

Langwig: Herd immunity is this idea that you’ve vaccinated or protected enough individuals in the population so that you’re able to control or even eradicate a disease. As a disease ecologist, we can make these calculations based on some really simple estimates, to know what proportion of the population has to be vaccinated in order for us to achieve a threshold at which we know that the reproductive rate of this pathogen is going to be less than one. It means essentially an epidemic will shrink.

If an individual gets infected, if every member of their group is protected by a vaccine, then that infection will not be transmitted to anyone else. That’s the most important goal, assuming these vaccines do block transmission, for us to achieve.

Q. Is herd immunity a goal for all vaccines, not just the COVID-19 vaccine?

Langwig: Absolutely. Our goal for vaccination is always to reach herd immunity, and that’s the way we actually eradicate pathogens or control diseases. For example, measles is this incredibly contagious disease. So, as a result of how contagious measles is, it means we have to have a huge fraction of the population vaccinated. We have to have over 90 percent of our population vaccinated in order to be at herd immunity levels.

Oftentimes, we get pockets of people in specific areas that are below that threshold. For whatever reason, this is part of the vaccine hesitancy issue that has arisen over the last decade. We are seeing U.S. outbreaks of vaccine preventable disease. So we have measles, which can be really well controlled by a vaccine, but we’re seeing it take hold through certain communities.

Q. How does getting a vaccine for yourself protect others?

Langwig: We are starting to learn this the hard way. When you get a vaccine, you’re not just protecting yourself, you’re protecting others around you.

There are going to be instances where for whatever reason a vaccine doesn’t work or maybe an individual can’t get it, perhaps due to age or certain allergies. When we decide not to get a vaccine, it means that we’re potentially putting another person at risk.

Q. How likely is it that people may have to get the COVID-19 vaccine more than once in the future, similar to a yearly flu shot?

Langwig: A major unknown about this [coronavirus] is how the strains are going to change.  As an epidemiologist, what I worry about the most are these new variants that have emerged and are circulating in South Africa and the U.K.

The reason the virus is evolving is because it’s having a lot of opportunities to evolve. The bigger your population size, the more opportunities you do have to change. So, as we get better at controlling this, we should have a better idea of what strains will be circulating. As we hopefully shrink the number of people infected, there should be less opportunity for it to evolve.

I would not be surprised at all in the future, if those vaccinated in the first round have to get the [COVID-19] vaccine again, due to mutations in the virus. It’s not uncommon at all that a vaccine would go through a change to modify the strains of the virus it targets. We do this for the flu vaccine every year. This isn’t nearly as complicated as developing the vaccines in the first place, but rather it is making a small modification to vaccines that already exist.

Interview by Jenny Kincaid Boone