The surge in measles outbreaks across the country during the past year absolutely highlights the importance of vaccinations. And Kate Langwig, an infectious disease ecologist and assistant professor in the Department of Biological Sciences is researching ways in which vaccine efficacy can be improved.
“For many infectious diseases, we rely on herd immunity to prevent outbreaks of vaccine-preventable infections. Herd immunity is the protection of the ‘herd,’ our population, by preventing infections in the vast majority of people,” Langwig said. “We can calculate the percentage of the population that needs to be vaccinated to prevent diseases from spreading and maintain herd immunity. For some pathogens, like measles, the number that needs to be vaccinated is very high because the measles virus spreads so easily.”
The measles vaccine has been shown to have 97 percent efficacy, but “understanding the circumstances that contribute to vaccine ineffectiveness can help to better protect populations,” Langwig said.
Langwig and her lab ran mathematical modeling simulations to determine if vaccine efficacy might be lower when individuals are exposed to high pathogen doses, and when individuals vary in their susceptibility. For example, if you have been vaccinated against the measles, but someone sneezes very close to your face, or you’re caring for a sick child who is sneezing, are you more likely to get sick?
Langwig and her lab found in their simulations that vaccines are predicted to be less effective at higher pathogen doses and when individuals in the population have similar susceptibility.
“Susceptibility, meaning how likely an individual is to get infected, is also important. Individuals that are younger or have poor nutrition can be more likely to get infected, even if they have been vaccinated. We found that populations that have more variable susceptibility have higher vaccine efficacy,” said Langwig, a member of the Global Change Center, an arm of the Fralin Life Sciences Institute.
Langwig and her lab, which includes undergraduate students, were interested in validating their simulations with some real-world data, so they did a systematic literature review to determine whether there were examples of diseases where vaccine efficacy is reduced at high doses.
“What we found was a bit of a shock — there are a very small number of studies that test whether vaccines are effective across multiple pathogen doses. We reviewed almost 6,000 articles and identified only about a dozen studies that had tested vaccines across multiple pathogen doses. Within those few studies, the pattern was generally consistent with our simulation — vaccine efficacy tended to be lower at high pathogen doses,” Langwig said.
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