Getting Full Series of Flu Vaccine Doses Increases Effectiveness

The study team behind a recent analysis showed that getting the recommended number of doses of the influenza vaccine led to higher vaccine effectiveness than partial vaccine over 4 flu seasons. The study was published online in JAMA Pediatrics.

The findings suggested that flu burden for children in the US could be reduced by improving adherence to a two-dose series of flu vaccinations in previously unvaccinated children.

Jessie Chung, MPH, and a team of investigators conducted the study in outpatient clinics at 5 sites of the US Influenza Vaccine Effectiveness Network from the 2014-2015 through the 2017-2018 flu seasons. The team aimed to learn patterns of vaccination in young children who received outpatient care for acute respiratory tract illness and compare vaccine effectiveness against laboratory-confirmed flu by how many vaccine doses were received.

Chung, from the Influenza Division at the Centers for Disease Control and Prevention, and the investigators analyzed children who presented with a cough of <8 days at 1 of the 5 study sites during the designated flu seasons. Patients were between 6 months and 8 years old.

The investigators collected combined nasal and oropharyngeal swab specimens that were tested for flu viruses using real-time, reverse-transcriptase polymerase chain reaction. Parents or guardians of the children completed an enrollment interview to answer questions about the child’s demographics and general health status.

Using electronic health records (EHRs), the investigators learned flu vaccination histories and doses received in the enrollment season.

Vaccine effectiveness was assessed through a test-negative design during each of the flu seasons. Effectiveness compared the odds of a positive test between vaccinated and unvaccinated participants.

Overall, 7533 children were included in the analysis—46% were girls, 62% were non-Hispanic white, and 65% were <5 years old. A majority of the children (68%) were first vaccinated before the current season, 12% were vaccinated for the first time in the current season, and 20% were never vaccinated.

Most of the children who were vaccinated had their first dose when they were <2 years old. The first type of vaccine given to 94% of the children was the inactivated flu vaccine.

Among the vaccinated children, 60% received 2 documented doses during their first vaccination season. These children were younger when they were first vaccinated (median, 8 months; IQR, 6-11) compared to those who only received 1 dose during their first vaccination season (median, 11 months; IQR, 6-18). The children who received 2 doses within their first vaccination season were more likely to be non-Hispanic white (68%) and have private health insurance (40%).

More than half (52%) of the children were unvaccinated in the enrollment season, 39% were fully vaccinated, and 9% were partially vaccinated. The adjusted vaccine effectiveness against any flu was 51% (95% CI, 44-57) among fully vaccinated children and 41% (95% CI, 25-54) among those who were partially vaccinated.

In a sample of 1519 children who were unvaccinated between the ages of 6 months and 2 years old, the effectiveness of 2 doses in the enrollment season was 53% (95% CI, 28-70) and 23% (95% CI, -11 to 47) for 1 dose. Children who had 2 doses were less likely to test positive for flu compared with those who only had 1 dose (aOR, .57; 95% CI, .35-.93).

The findings were consistent with US flu vaccine recommendations and suggested that there should be more promoting efforts made to improve flu vaccine coverage, particularly with 2 doses in the first vaccination season.

This story was originally featured on HCPLive.