What role can health policy and systems research play in supporting responses to COVID-19 that strengthen socially just health systems? by Gilson, L, Marchal, B, Ayepong, I, Barasa, E, Dossou, J-P, George, A, Guinaran, R, Maceira, D, Molyneux, S, Prashanth, NS, Schneider, H, Shawar, Y, Shiffman, JR, Sheikh, K, Spicer, N, Van Belle, S, Whyle, E