Data collection
Once one case was confirmed by laboratory testing, the epidemiological
and clinical criteria and medical records were submitted and accepted by
LACDC immediately. After the receipt of the submitted reports, the LACDC
performed an epidemiological investigation within 24 h, including
verification of the activity trajectory, close contact determination,
and tracing. General information (such as name, sex, age, ID number,
last exposure time, frequency of exposure, mode of exposure, and
location of exposure) of confirmed and asymptomatic infections between 4
April 2022 and 20 April 2022 in Lu’an was extracted from the
epidemiological survey reports and National Notifiable Diseases Registry
System (NNDRS), which is a web-based computerized reporting system and
has been in operation since 2004 in China[25].
Clinical information was obtained from epidemiological survey reports.
We obtained the following information from the Anhui Immunization
Information Management System (AIIMS) through the ID numbers and names
of the individuals: vaccine type, vaccination dose, vaccination site,
vaccine manufacturer, vaccination date, vaccination status, and all
vaccination records. We considered vaccinations to be valid only if
documented in either the national or the provincial immunization
information system.
Vaccination data
Three types of vaccines including inactivated, Ad5-nCoV, and recombinant
protein vaccines against SARS-CoV-2 were authorized and widely used in
China[26]. Vaccination was considered incomplete
if the time from the last dose of vaccination to the last exposure time
was less than 14 days. We divided all participants into four groups:
unvaccinated (zero doses, or first dose<14 days from time of
last exposure), partial vaccination (one-dose inactivated vaccine or
two-dose recombinant protein vaccine, with the last dose of vaccination
>14 days from the time of last exposure), full vaccination
(one-dose Ad5-nCoV vaccine or two-dose inactivated vaccine or three-dose
recombinant protein vaccine, with the last dose of vaccination
>14 days from the time of last exposure), and booster
vaccination (three-dose of any COVID-19 vaccine, or two-dose Ad5-CoV
vaccine, or three-dose recombinant protein vaccine, or two-dose any
inactivated vaccine with a one-dose Ad5-CoV vaccine/recombinant protein
vaccine, with the last dose of vaccination >14 days from
the time of last exposure)[27,28]. Additionally,
homogenous booster vaccination (same as the primary vaccine) and
heterologous booster vaccination (third dose with an Ad5-nCoV or
recombinant protein vaccine) following a two-dose regimen of inactivated
vaccines were included in our study[24,29].