From the Journals

Delaying flu vaccine didn’t drop fever rate for childhood immunizations



Fevers were no less common or less severe when influenza vaccine was delayed 2 weeks for children receiving DTaP and pneumococcal vaccinations, according to a randomized trial.

A close-up of medical syringe with a vaccine. MarianVejcik/Getty Images

An increased risk for febrile seizures had been seen when the three vaccines were administered together, wrote Emmanuel B. Walter, MD, MPH, and coauthors, so they constructed a trial that compared a simultaneous administration strategy that delayed inactivated influenza vaccine (IIV) administration by about 2 weeks.

In all, 221 children aged 12-16 months were enrolled in the randomized study. A total of 110 children received quadrivalent IIV (IIV4), DTaP, and 13-valent pneumococcal conjugate vaccine (PCV13) simultaneously and returned for a dental health education visit 2 weeks later. For 111 children, DTaP and PCV13 were administered at study visit 1, and IIV4 was given along with dental health education 2 weeks later. Most children in both groups also received at least one nonstudy vaccine at the first study visit. Eleven children in the simultaneous group and four in the sequential group didn’t complete the study.

There was no difference between study groups in the combined rates of fever on the first 2 days after study visits 1 and 2 taken together: 8% of children in the simultaneous group and 9% of those in the sequential group had fever of 38° C or higher (adjusted relative risk, 0.87; 95% confidence interval, 0.36-2.10).

However, children in the simultaneous group were more likely to receive antipyretic medication in the first 2 days after visit 1 (37% versus 22%; P = .020), reported Dr. Walter, professor of pediatrics at Duke University, Durham, N.C., and coauthors. Because it’s rare for febrile seizures to occur after immunization, the authors didn’t make the occurrence of febrile seizure a primary or secondary endpoint of the study; no seizures occurred in study participants. They did hypothesize that the total proportion of children having fever would be higher in the simultaneous than in the sequential group – a hypothesis not supported by the study findings.

Children were excluded, or their study vaccinations were delayed, if they had received antipyretic medication within the 72 hours preceding the visit or at the study visit, or if they had a temperature of 38° C or more.

Parents monitored participants’ temperatures for 8 days after visits by using a study-provided temporal thermometer once daily at about the same time, and also by checking the temperature if their child felt feverish. Parents also recorded any antipyretic use, medical care, other symptoms, and febrile seizures.

The study was stopped earlier than anticipated because unexpectedly high levels of influenza activity made it unethical to delay influenza immunization, explained Dr. Walter and coauthors.

Participants were a median 15 months old; most were non-Hispanic white and had private insurance. Most participants didn’t attend day care.

“Nearly all fever episodes and days of fever on days 1-2 after the study visits occurred after visit 1,” reported Dr. Walter and coinvestigators. They saw no difference between groups in the proportion of children who had a fever of 38.6° C on days 1-2 after either study visit.

The mean peak temperature – about 38.5° C – on combined study visits 1 and 2 didn’t differ between groups. Similarly, for those participants who had a fever, the mean postvisit fever duration of 1.3 days was identical between groups.

Parents also were asked about their perceptions of the vaccination schedule their children received. Over half of parents overall (56%) reported that they disliked having to bring their child in for two separate clinic visits, with more parents in the sequential group than the simultaneous group reporting this (65% versus 48%).

Generalizability of the findings and comparison with previous studies are limited, noted Dr. Walter and coinvestigators, because the composition of influenza vaccine varies from year to year. No signal for seizures was seen in the Vaccine Safety Datalink after IIV during the 2017-2018 influenza season, wrote the investigators. The 2010-2011 influenza season’s IIV formulation was associated with increased febrile seizure risk, indicating that the IIV formulation for that year may have been more pyrogenic than the 2017-2018 formulation.

Also, children deemed at higher risk of febrile seizure were excluded from the study, so findings may have limited applicability to these children. The lack of parental blinding also may have influenced antipyretic administration or other symptom reporting, although objective temperature measurement should not have been affected by the lack of blinding, wrote Dr. Walker and collaborators.

The study was funded by the Centers for Disease Control and Prevention. One coauthor reported potential conflicts of interest from financial support received from GlaxoSmithKline, Sanofi Pasteur, Pfizer, Merck, Protein Science, Dynavax, and Medimmune. The remaining authors have no relevant financial disclosures.

SOURCE: Walter EB et al. Pediatrics. 2020;145(3):e20191909.

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