More girls than boys are being infected with HIV by their mothers, researchers have said.
The nine-year study was carried out by the Ministry of Health, the Kenya Medical Research Institute (Kemri), and the Clinton Health Access Initiative, US, to assess the status of mother-to-child HIV transmission in the country.
One of its key and surprising findings was that more girls than boys were getting HIV through infected mothers.
The study published last week assessed the HIV status of 365,841 Kenyan infants aged below two years from January 2007-July 2015.
The researchers reported a significant gender imbalance in mother-to-child HIV transmission.
"Overall, we observed slightly higher odds of positivity in female infants compared to male infants from birth to six weeks," observed the researchers.
The study was led by Dr Matilu Mwau of Kemri and Dr Martin Siengo, head of the National Aids and STI Control Programme, who said the finding was hardly by chance.
"This phenomenon has been described previously and there are theories that female infants may be more susceptible to HIV infection in the womb and soon after birth," says the study.
The scientists also hypothesise that more of HIV-infected male infants die before birth compared to girls, hence more infected female live births.
The authors however called for more studies to better understand the phenomenon. They pointed out that despite huge efforts and gains in controlling mother-to-child HIV transmission, thousands of children were still being infected. At greatest risk, the study says, are infants whose infected mothers are not on treatment, babies not on preventive drugs, and those on mixed breastfeeding.
"Thousands of infants are still becoming infected each year because their mothers are not enrolled in care," says the study.
The researchers said many mothers and infants in Kenya have no access HIV care.
"Barriers to care include distance to health facility and transportation costs, facility inefficiencies such as stock-outs and long wait times, and persistent stigma," they said.
The situation is compounded by the fact that many women go to health facilities late, with a considerable number delivering at home. The scientists observed cases where infants were infected despite their mothers being on HIV medication.