Numbered align with bracket

Question

I have the following code

\begin{align}
s'(t) &= -\beta s(t) i(t)\\
i'(t) &= \beta s(t) i(t) - \gamma i(t)\\
r'(t) &= \gamma i(t),
\end{align}

and I want to enclose this with a bracket like a case, but maintaining the numbered equations.

Answer 1

Simple with empheq. Needless to load amsmath, as it loads mathtools, which loads amsmath:

\documentclass{article}
\usepackage[overload]{empheq}

\begin{document}

\begin{align}[left=\empheqlbrace]
    s'(t) &= -\beta s(t) i(t)\\
    i'(t) &= \beta s(t) i(t) - \gamma i(t)\\
    r'(t) &= \gamma i(t),
\end{align}

\end{document}