\begin{tikzpicture}
	\begin{pgfonlayer}{nodelayer}
		\node [style=circle] (0) at (-5, 5) {Simulations};
		\node [style=circle] (1) at (5, 5) {Curves};
		\node [style=circle] (3) at (-5, -5) {Data};
		\node [style=circle] (4) at (5, -5) {};
		\node [style=circle] (5) at (0, 0) {SARS-CoV-2};
		\node [style=circle] (6) at (11, 0) {};
		\node [style=circle] (7) at (11, 0) {};
		\node [style=circle] (8) at (11, 0) {Bodies};
	\end{pgfonlayer}
	\begin{pgfonlayer}{edgelayer}
		\draw [style=edge] (3) to (0);
		\draw [style=edge] (0) to (1);
		\draw [style=edge, in=90, out=15, loop] (1) to ();
		\draw [style=edge] (1) to (4);
		\draw [style=edge] (4) to (3);
		\draw (5) to (8);
		\draw [style=edge, in=180, out=90, loop] (0) to ();
	\end{pgfonlayer}
\end{tikzpicture}