Infants too young for vaccination were hospitalized with Covid-19 more often than any age group other than the elderly during the omicron BA.5 wave over the summer, according to the Centers for Disease Control and Prevention.
The CDC, in a report published Thursday, found that hospitalizations among infants younger than six months surged elevenfold from April through July of this year when omicron BA.2 and subsequently BA.5 were the dominant variants circulating.
The average weekly hospitalization rate among young infants during this period was about 13.7 per 100,000. This was about the same as patients ages 65 to 74 at 13.8 per 100,000. It was more frequent than all other children and adults younger than 65, according to the CDC report.
Fortunately, the surge in hospitalizations among young infants was not associated with increased severity. In fact, the length of hospital stay and the proportion of admissions that needed intensive care was actually lower during omicron than when the delta variant was dominant, the report found.
The spike in hospitalizations among young infants was due to high community transmission of the virus during omicron, according to CDC. The threshold for admitting young infants is also much lower than older children. Adolescents and adults younger than age 65 also had more immunity due to vaccination, infection or both which likely kept their hospitalization rates down, according to the report.
The authors of the report said the elevated hospitalization rate underscores the importance of pregnant mothers staying up to date on their Covid vaccines, including getting the new booster shot that targets omicron BA.5. Infants younger than six months are the only age group in the U.S. ineligible for the shots.
Two doses of Covid vaccine given to the mother during pregnancy is about 52% effective at preventing hospitalization among infants younger than six months, according to CDC. This is likely due to the mothers protective antibodies induced by vaccination transferring to the fetus during pregnancy.
The CDC and the American College of Obstetricians and Gynecologists recommend Covid vaccination for women who are pregnant, trying to get pregnant or breastfeeding.
Young infants born during the omicron BA.5 dominant period may have had less protection against disease because many mothers received their vaccines before pregnancy and immunity waned as more time had passed since their last dose, according to the report. In addition, BA.5 and other emerging variants are simply more adept at evading the protection provide vaccines.