Children younger than 5 years whose parents were vaccinated against COVID-19 appeared to be at reduced risk of hospitalization during the Delta and Omicron variant waves in France, according to a research letter published yesterday in JAMA Network Open.
Universite de Paris-Cite researchers led the observational study of 163 preschoolers hospitalized during the Delta (39%) and Omicron (58%) periods from May 12, 2021, to Feb 14, 2022. During the study period, French children in that age-group were not eligible for COVID-19 vaccination, while the rate of two-dose vaccination in adults rose from 7% to 92%.
The data were extracted from the COVID-19 Pediatric Observatory (PANDOR) surveillance study of hospitalized pediatric COVID-19 patients in France.
The estimated hazard ratios for hospitalization among children with vaccinated versus unvaccinated parents were 0.03 (95% confidence interval [CI], 0.02 to 0.06) during the Delta era and 0.21 (95% CI, 0.14 to 0.33) amid Omicron, or 97% and 79% protection, respectively.
"The association between parent vaccination and reduced risk of admission for SARS-CoV-2 in children younger than 5 years suggests that parents played a major role in transmitting SARS-CoV-2 to their young children during both waves, but the association between protection and vaccination seemed lower in the Omicron vs Delta period," the study authors wrote. "The Omicron variant has been shown to be more transmissible, and the vaccine effectiveness against infection seems lower."
The researchers noted that the study didn't consider whether the children had siblings, other potential sources of infection in the household, environmental changes, lockdowns, compliance with physical distancing, dates of parental vaccination, or receipt of booster vaccines, the latter of which constitutes a bias, considering the change in vaccine effectiveness over time and across variants.
"These results should not be extrapolated to other variants, such as the predominant [Omicron] variants BA.4 and BA.5," they wrote. "Nonetheless, these results reinforce recommendations for widespread vaccination of parents of young children."