Effect of Inactivated Influenza Vaccine & Immunogenicity in
A Study was conducted to systematically review studies comparing vaccine effectiveness (VE) and immunogenicity after 1 or 2 doses of inactivated influenza vaccine (IIV) in children.

Researchers included studies published in a peer reviewed journal with children aged 6 months through 8 years.

VE among fully and partially vaccinated children was compared with that of unvaccinated children. Researchers extracted geometric mean titers of serum hemagglutination inhibition (HAI) antibodies against influenza A(H1N1), A(H3N2), and B-lineage vaccine antigens after 1 and 2 IIV doses. Outcomes were evaluated by age, timing of doses, vaccine composition, and prevaccination titers.

--A total of 10 VE and 16 immunogenicity studies were included.

--VE was higher for fully vaccinated groups than partially vaccinated groups, especially for children aged 6–23 months.

--The findings show increased HAI titers after 2 doses, compared with 1.

--Older children and groups with prevaccination antibodies have robust HAI titers after 1 dose. Similar vaccine strains across doses, not the timing of doses, positively affects immune response.
Researchers typically administered one-half the standard dose of IIV. HAI antibodies are an imperfect correlate of protection.

In particular, findings supports policies recommending 2 IIV doses in children to provide optimal protection against influenza.

Source: https://pediatrics.aappublications.org/content/147/6/e2020019901?rss=1