  Background: Here we investigate whether releasing COVID-19 vaccines in
limited quantities and at limited times boosted Italy's vaccination campaign in
2021. This strategy exploits insights from psychology and consumer marketing.
Methods: We built an original dataset covering 200 days of vaccination data in
Italy, including 'open day' events. Open-day events (in short: open days) are
instances where COVID-19 vaccines were released in limited quantities and only
for a specific day at a specified location (usually, a large pavilion or a
public building). Our dependent variables are the number of total and first
doses administered in proportion to the eligible population. Our key
independent variable is the presence of open-day events in a given region on a
specific day. We analyzed the data using regression with fixed effects for time
and region. The analysis was robust to alternative model specifications.
Findings: We find that when an open day event was organized, in proportion to
the eligible population, there was an average 0.39-0.44 percentage point
increase in total doses administered and a 0.30-0.33 percentage point increase
in first doses administered. These figures correspond to an average increase of
10,455-11,796 in total doses administered and 8,043-8,847 in the first doses
administered. Interpretation: Releasing vaccines in limited quantities and at
limited times by organizing open-day events was associated with an increase in
COVID-19 vaccinations in most Italian regions. These results call for wider
adoption of vaccination strategies based on the limited release of vaccines for
other infectious diseases or future pandemics.
