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Recent spectroscopic measurements of the equivalent widths of the resonant BeII doublet and Ca II K lines and their ratios in expanding nova ejecta indicatesurprisingly high abundances of $^7$Be with a typical mass fraction$X_\mathrm{obs}(^7\mathrm{Be}) = 10^{-4}$. This is an order of magnitude largerthan theoretically predicted values of $X_\mathrm{theor}(^7\mathrm{Be})\sim10^{-5}$ for novae. We use an analytical solution of the $^7$Be productionequations to demonstrate that $X_\mathrm{theor}(^7\mathrm{Be})$ is proportionalto the $^4$He mass fraction $Y$ in the nova accreted envelope and then weperform computations of 1D hydrostatic evolution of the $1.15\,M_\odot$ CO novamodel that confirm our conclusion based on the analytical solution. Ourassumption of enhanced $^4$He abundances helps to reduce, although notcompletely eliminate, the discrepancy between $X_\mathrm{obs}(^7\mathrm{Be})$and $X_\mathrm{theor}(^7\mathrm{Be})$. It is supported by UV, optical and IRspectroscopy data that reveal unusually high values of $Y$ in nova ejecta. Wealso show that a significantly increased abundance of $^3$He in nova accretedenvelopes does not lead to higher values of $X_\mathrm{theor}(^7\mathrm{Be})$because this assumption affects the evolution of nova models resulting in adecrease of both their peak temperatures and accreted masses and, as aconsequence, in a reduced production of $^7$Be.

An evidence-based assumption that helps to reduce the discrepancy between the observed and predicted $^7$Be abundances in novae