https://www.theguardian.com/science/2023/jan/14/immunity-debt-does-it-really-exist

Some claim the rise in winter infections has been caused by the reduction of seasonal bugs during lockdowns. But experts are sceptical about these oversimplified explanations

The deaths of at least 74 people, including 19 children, from the invasive bacterial infection group A streptococcus, or strep A, are the most extreme consequences of a wave of winter infections that have seemingly left most of the country coughing and sneezing. The parlous state of the nation’s health has prompted suggestions that we are now paying an “immunity debt” incurred by the reduction of common infections during the Covid-19 lockdowns of 2020 and 2021. But experts seem divided about whether the debt concept is genuine, let alone whether it explains the prevalence of non-Covid afflictions.