Two Doses of Flu Vaccine Provides Optimal Protection in Youn
A literature review offers strong endorsement for public-health policies advising two doses of inactivated influenza vaccine in children aged six months through eight years to provide optimal protection against influenza, report researchers with the U.S. Centers for Disease Control and Prevention (CDC).

Both the U.S. Advisory Committee on Immunization Practices (ACIP) and the World Health Organization (WHO) recommend two doses of influenza vaccine before the start of influenza season for children 6 months through 8 years, during their first season of vaccination.

"However, administering two doses of influenza vaccine during the same season is logistically challenging because it may require extra clinic visits and, ideally, should be done before influenza virus circulation," CDC researcher Dr. Fatimah Dawood and colleagues note in Pediatrics.

They did a systematic literature review to summarize the current evidence on antibody immune responses and effectiveness of two versus one dose of inactivated influenza vaccine among vaccine-naive children aged 6 months through 8 years during their first season of vaccination. They made four key observations.

"First, a full two-dose influenza vaccine series in children receiving influenza vaccine for the first time provides optimal protection against influenza-related medical visits in the first season of vaccination. Higher effectiveness is observed among fully vaccinated children, compared with partially vaccinated children, and two doses of vaccine are more immunogenic than one dose," the team reports.

Second, children younger than 2 years, who are less apt to have had a first influenza infection, may benefit the most from a second dose of influenza vaccine.

Third, children with positive prevaccination titers and who are older - and therefore more likely to have been exposed to influenza naturally - may have a protective immune response after a single dose of influenza vaccine.

Finally, the data suggest that the timing between two doses of influenza vaccine or schedule (i.e., administering doses across seasons) does not appear to negatively affect the immune response when antigen components are similar.

The team say further research is needed to determine if the imprinting benefits of early vaccination in immunologically naive children could provide durable and broad protection against homosubtypic and heterosubtypic strains. "Imprinting children through optimal vaccination strategies could have far reaching benefits for the control of seasonal influenza and improving public health," they conclude.

Source:
https://pediatrics.aappublications.org/content/early/2021/05/25/peds.2020-019901
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