Received: 24 September 2020
Accepted: 14 December 2020
First Online: 11 January 2021
Ethics approval and consent to participate
: Ethics approval was obtained from the University of Cape Town Faculty of Health Sciences Human Research Ethics Committee (Human Research Ethics committee reference numbers 401/2009 and 651/2013) and the Provincial Child Health Research committee. Mothers provided written informed consent at enrolment and annually.
: Not applicable.
: The authors declare that they have no competing interests.