COVID-19 vaccine protects vaccinated children but may not prevent transmission to unvaccinated: IU News

Note for journalists: This study was published as a working paper by the National Bureau of Economic Research on October 16. References to these results should include their pre-publication status and a note that the results have not been peer-reviewed, meaning that they have not been reviewed by a group of peer scientists in the field of study.

BLOOMINGTON, Indiana — New research from Indiana University on COVID-19 immunizations in school-age children suggests that vaccinating a child provides strong protection for themselves, but may provide less protection than expected for other unvaccinated children.

Preliminary results from a study by researchers at IU and the University of Wisconsin-Madison, released as a National Bureau of Economic Research working paper prior to peer review, show that the COVID-19 vaccine is effective in preventing disease in vaccinated individuals is effective, increases in school-wide immunization rates did not provide a measurable protection against transmission of the virus to unvaccinated students.

Seth Freedman.

Seth Freedman, an associate professor at IU’s Paul H. O’Neill School of Public and Environmental Affairs, said this means that unvaccinated children are not necessarily around vaccinated children.

“It’s really important to know if vaccinating a person prevents the virus from spreading to other unvaccinated peers, especially in an environment like schools,” Freedman said. “Our study suggests that this is not the case, at least when vaccination rates are fairly low overall. But we also find that school-age children who were vaccinated received really strong protection for themselves.”

Key findings from the paper show that:

  • The effects of the vaccine in the real world were similar to the effects seen in clinical trials. In children who received the vaccine earlier because they were earlier eligible, the study finds that the vaccine was 80% effective at preventing infection.

  • Increasing school-wide immunization rates from 5% to 25% did not reduce the likelihood of unvaccinated students catching COVID-19.

Freedman and co-authors Kosali Simon and Coady Wing of IU and Dan Sacks of the UW-Madison Wisconsin School of Business studied two cohorts of children across two school years, 2020-21 and 2021-22, using linked data from the Indiana Vaccine Registry. PCR COVID-19 test registry and a large data system for electronic medical records.

The team studied the direct effects of the vaccine, ie how much it protects those vaccinated, by following a grade 5 to grade 6 control group and a grade 6 to grade 7 treatment group over a two-year period. While neither group was eligible for a vaccine in the first year due to age requirements, the treatment group became vaccinable in the second year. The number of COVID-19 cases in the first year was the same for both groups, but the treatment group had a lower number of COVID-19 cases in the second year.

For children who received the vaccine earlier because they were earlier eligible, research finds that t...

In children who received the vaccine earlier because they were earlier eligible, the study finds that the vaccine was 80% effective at preventing infection. Photo by Getty Images

Quantitatively, the researchers found that the vaccine’s direct action reduced COVID-19 incidence by about 80% – similar to what was found in clinical trials of vaccines.

To examine the indirect effects of the vaccine, the researchers focused on sixth graders in both years, who largely failed to vaccinate in both years. In Indiana, some sixth graders go to elementary schools (K-6) and others go to middle schools (usually grades 6-8). This means that the sixth-graders of the middle school sophomores attended school with vaccinated seventh- and eighth-graders; About a quarter of their school was vaccinated. In contrast, the sixth graders in elementary school had unvaccinated classmates; less than 5% of their school was vaccinated.

If there were large spillover effects from the vaccine, the researchers expected the number of COVID-19 cases among middle school sixth-graders who went to school with vaccine-eligible peers to decrease. However, the study found similar levels of COVID-19 in middle school and elementary school sixth graders.

Therefore, the indirect effects were small, at least given the level of vaccine uptake among Indiana youth at the time, which was below 30%.

“One important caveat is that we’re looking at a group where vaccination coverage is low,” Sacks said. “And for a truly contagious disease like COVID-19, you may need a much higher vaccination rate before the indirect effects start to matter.”

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