COVID Spreads Easily Between Schools and Families: Getting 5-11 Year Olds Vaccinated is Important

Kids ages 5-11 became eligible for vaccination on November 3rd. That means that there are nearly 45,000 kids in Dane County (8% of the total population) who can now get vaccinated! We’re all very excited, but have also been wondering: what impact might this have on the spread of COVID in our community? We looked at 86 households where someone age 5-11 tested positive and someone 12+ tested positive to see how COVID was spreading in these scenarios. Here is what we found:

Kids ages 5-11 are being impacted by COVID

Most K-12 schools began fall instruction in the beginning of September. Since then, kids ages 5-11 have had a significantly higher case rate than every other age group:

Figure 1. Cases per 100,000 population by age group, 9/1/21 – 11/20/21

 

Ages 35-44 have the next highest rates, and ages 25-34 and 35-44 have the highest raw numbers of cases, and these would include most parents of the 5-11 age group. When comparing case rates by vaccination status, children under the age of 12 who were not eligible to be vaccinated during this timeframe have higher case rates than all age groups of vaccinated people, but have one of the lowest case rates among all age groups of unvaccinated people.

It is common for children to bring COVID home from schools

We were able to figure out the “index case” (the person who first got COVID) for 78 out of 86 families. Out of the 78 index cases, 40 were under the age of 12 (39 were ages 5-11).  Out of the 40 families where a child under 12 brought COVID home, more than two-thirds of those children likely got COVID from school. Out of all 78 families where we were able to identify an index case, 40% likely got COVID from school, 9% were likely exposed at work, and 31% had an undetermined source of exposure. While this is just a sample and doesn’t represent all of Dane County, it does suggest that school is an important factor in spreading COVID both to children and adults.

Vaccinating 5-11 year olds will likely be a key tool in reducing COVID in our community

We’ve consistently been seeing around one-third of our cases getting COVID from someone in their own home. Since all kids ages 5-11 live with at least one other person, it makes sense that if they are exposed at school they can easily bring COVID home and spread it to others.

Getting 5-11 year olds vaccinated will help keep 5-11 year olds healthy, and prevent school disruptions. It will also likely prevent some spread among adults—parents or caregivers who get sick when they are caring for children. That’s a big win and a lot of great reasons to get 5-11 year olds vaccinated!

If you’re interested in diving into the details of how we figured this out, see below:

How we analyzed the data

Methods

Due to our case investigation data showing that there have been a lot of cases affiliated with school clusters over the past couple months (last page of each data snapshot), we hypothesized that a substantial number of kids were getting COVID at school, then bringing it home and spreading it to other members of their household. In order to test this hypothesis, we:

• First identified all cases among 5-11 year olds in a recent two week period (10/18/21 – 10/31/21) to make sure we had a current understanding of what transmission looked like right before 5-11 year olds became eligible for vaccination.
• Next, we zoomed into the scenarios where there was another case within the same household around the same time, so we could try to understand household transmission patterns.
• From this group, we looked at households with both at least one 5-11 year old case and one 12+ year old case in order to look at potential spread between vaccinated and unvaccinated household members.

Figure 2. Flowchart of cases included in analysis

 

From this sample of 86 households, we used case investigation data to try and determine which case was the index case in each household (the first person who became infected and potentially spread COVID to the other members of the household). This was determined by looking at the date of symptom onset, the test date, case investigation notes, the likely source of exposure* for each individual, and whether each individual was linked to any known clusters (such as a school cluster or workplace cluster).

*The most likely source of exposure is derived from a section of questions that was added to the Wisconsin Electronic Disease Surveillance System in May 2021. Prior to this date, the source of exposure was not able to be easily compiled and analyzed.

Results

Overview of index and secondary cases within the 86 households with likely household transmission

Among the 86 households, there was a total of 78 index cases, 190 secondary cases (non-index cases), and 14 cases (among six households) where it could not be determined whether they were the index case or not. We found that of the 78 known index cases, 45 (58%) were children and 33 (42%) were adults. The index case was unable to be determined in 6 of the 86 households (7%), and in two of the households (2%), there was no index case due to each individual having the same common exposure outside of the household.

Table 1. Index and secondary cases of 86* households by child/adult and vaccination status

 *Two households were not included in the “index cases” column because each person in the household was a secondary case due to each individual having the same common exposure outside of the household.

Note that although there were more vaccinated adult cases than unvaccinated adults, only about 17% of adults in Dane County are not fully vaccinated, while 33% of adult index cases and 23% of adult secondary cases in this analysis were unvaccinated adults. (For more on rates of infection after vaccination, visit our weekly data snapshot).

Table 2. 78 known index cases and 190 known secondary cases by age group

Where each index case was most likely exposed

It’s important to know where people are getting infected so that we can break chains of transmission before people contract and then spread the virus to other people within their household. We identified the most likely source of exposure for each index case by examining case interview data and whether each individual was linked to any known clusters (such as a school cluster or workplace cluster).

Table 3. Most likely source of exposure for index cases under age 12 and age 12+

Out of the 40 index cases of children under the age of 12, more than two-thirds likely contracted COVID from school. Out of all 78 known index cases, 31 (40%) were likely exposed at school, 7 (9%) were likely exposed at work, and 24 (31%) had an undetermined source of exposure.

When spread is happening within households that have kids ages 5-11, most commonly the cluster is initiated when an unvaccinated child brings it into the household, and that child appears more often than not to be getting it from school. We know that unvaccinated people are significantly more likely to test positive for COVID, and vaccinated kids ages 12-17 have consistently had the lowest case rates among all age groups in Dane County for at least the past three months. Therefore, vaccinating kids ages 5-11 will reduce the number of cases in this age group, which will also reduce the number of cases and quarantines in schools, and reduce the spread that is occurring in households with kids. This finding is supported by recent research that examined a large outbreak that spread to factories and families via children in school, and concluded “children aged less than 12 years may be critical hidden spreaders, which indicates an urgent need of vaccination for this particular population.”