More shots, then more covid infections?

The short version: the evidence here does not answer whether more shots increase infection risk. It shows the opposite—that boosters reduce infection risk in the short term.

The retrieved studies consistently report that additional doses lower the chance of catching COVID-19, at least for a few months. A large matched cohort in Sicily found a booster dose was about 75% effective against infection during the Omicron wave [1]. An Italian healthcare worker study reported 95% effectiveness against infection after the second dose [2]. A small Toledo practice found that people infected less than 15 days after a booster had a 60% lower relative risk of symptomatic infection than those infected later [3].

But these studies have limits that matter. They compare the boosted to the primary-cycle-only group, not to the unvaccinated [1][2]. They follow people for only 90 days [1] or a few months [2][3]. Waning is built into the design: the Sicily study stopped at 90 days [1], and the Toledo study's own data shows that most breakthrough infections happened 15 days or more after the booster [3]. A narrative review notes that neutralizing antibodies decline from three months after vaccination and are nearly absent by six months [4]. So the evidence shows a temporary reduction in infection risk, not a permanent one.

What the retrieval does not contain: any study comparing infection rates in people with 3, 4, or 5+ doses to people with fewer doses over a longer period, or any study that tracks infection risk after the first few months post-booster. The question of whether repeated boosting eventually increases susceptibility—through immune imprinting or repertoire narrowing—is not addressed by these records.

My call: the evidence here shows that additional doses reduce infection risk for about 3 months. It does not answer whether more shots eventually lead to more infections over a longer time horizon. Confidence: moderate for the short-term benefit; not clear for the long-term question.