Postvaccination Fever Response Rates in Children Derived Using the Fever Coach Mobile App: A Retrospective Observational Study

Abstract

Background: Postvaccination fever is a mild adverse event that naturally improves without complications, but is highly prevalent and can be accompanied by febrile convulsions in some cases. These adverse effects may cause parents to delay or avoid vaccinating their children.

Objective: This study aimed to identify postvaccination fever patterns and the ability of antipyretics to affect changes in these patterns from data collected from a mobile app named Fever Coach.

Methods: Data provided by parents of feverish children derived from a mobile app, Fever Coach, were used to identify postvaccination fever patterns according to vaccinations and the use of antipyretic drugs. We selected single vaccination records that contained five or more body temperature readings performed within 48 hours of vaccination, and we analyzed postvaccination fever onset, offset, duration, and maximum body temperature. Through observing the postvaccination fever response to vaccination, we identified the effects of antipyretic drugs on postvaccination fever onset, offset, and duration times; the extent of fever; and the rate of decline. We also performed logistic regression analysis to determine demographic variables (age, weight, and sex) involved in relatively high fevers (body temperature ≥39°C).

Results: The total number of Fever Coach users was 25,037, with 3834 users having entered single vaccination records, including 4448 vaccinations and 55,783 body temperature records. Most records were obtained from children receiving the following vaccinations: pneumococcus (n=2069); Japanese encephalitis (n=911); influenza (n=669); diphtheria, tetanus, and pertussis (n=403); and hepatitis A (n=252). According to the 4448 vaccination records, 3427 (77.05%) children had taken antipyretic drugs, and 3238 (89.15%) children took antibiotics at body temperatures above 38°C. The number of children taking antipyretics at a body temperature of 38°C was more than four times that of those taking antipyretics at 37.9°C (307 vs 67 cases). The number of instances in which this temperature threshold was reached was more than four times greater than the number when the temperature was 37.9°C. A comparative analysis of antipyretic and nonantipyretic cases showed there was no difference in onset time; however, offset and duration times were significantly shorter in nonantipyretic cases than in antipyretic cases (P<.001). In nonantipyretic cases, offset times and duration times were 9.9 and 10.1 hours shorter, respectively, than in antipyretic cases. Body temperatures also decreased faster in nonantipyretic cases. Influenza vaccine-associated fevers lasted relatively longer, whereas pneumococcus vaccine-associated fevers were relatively short-lived.

Conclusions: These findings suggest that postvaccination fever has its own fever pattern, which is dependent on vaccine type and the presence of antipyretic drugs, and that postvaccination temperature monitoring may ease fever phobia and reduce the unnecessary use of antipyretics in medical care.

Keywords: digital health care; mobile app; patient-generated health data; postvaccination fever; vaccination.

Figure 1

Screenshots of vaccination and fever response in the Fever Coach app. The left screen (“Today’s Records”), middle screen (“Enter the temperature”), and right screen (“Enter the dose”) have areas for user-input data. The functions corresponding to vaccination data, fever response, and antipyretic data in the three screens are indicated with dotted boxes. The original app showed Korean menu names; for international use, they have been translated into English.

Figure 2

Onset, offset, and duration time definitions. The x-axis represents the time since vaccination and the y-axis represents the body temperature. The blue dot represents the actual body temperature. The black line between the blue dots is the imputated body temperature.

Figure 3

Data collection flowchart.

Figure 4

Time of first administration of antipyretic after vaccination and body temperature at the time of antipyretic use.

Figure 5

Comparison of onset, offset, duration times, and maximum temperatures among vaccine types, and the effects of antipyretics on postvaccination fever response. From left to right: box plots of onset, offset, duration times, and maximum body temperature are depicted. The bar indicates the median; x indicates the mean.

Figure 6

Body temperature graph over time for each vaccine showing the effects of antipyretic administration. The empty circle indicates the mean; the error bar represents a 95% confidence interval.