  We develop a clear theoretical description of radial swelling in virus-like
particles which delineates the importance of electrostatic contributions to
swelling in absence of any conformational changes. The model couples the
elastic parameters of the capsid -- represented as a continuous elastic shell
-- to the electrostatic pressure acting on it. We show that different
modifications of the electrostatic interactions brought about by, for instance,
changes in $pH$ or solution ionic strength, are often sufficient to achieve the
experimentally-observed swelling (about 10% of the capsid radius).
Additionally, we derive analytical expressions for the electrostatics-driven
radial swelling of virus-like particles, which enable one to quickly estimate
the magnitudes of physical quantities involved.
