
the survey. Following the pre-pandemic POLYMOD study, a contact is defined as either
a skin-to-skin contact such as a kiss or a handshake (physical contact) or an exchange of
words in the presence of another person (non-physical contacts) [1]. Participants were
asked to report the age group, gender, relation, the contact setting (e.g. home, school,
workplace, place of entertainment, etc.), and whether the contact was a household
member. For survey waves 1 and 2, participants were asked to provide each contact’s
information separately. However, some participants reported contacts to groups of
individuals (e.g., customers, clients) for which a specific number of contacts was
assumed (Additional file 2 of [9]). From wave 3 onwards, participants were given the
possibility to record group contacts in addition to the recording of individual contacts.
Additionally, some participants could not recall or preferred not to answer the age or
gender information of some individual contacts. We treat these three types of entries
with missing age or gender equally and refer to them as missing &aggregate contact
reports. A copy of the COVIMOD questionnaire may be found in Additional file 1 of [9].
COVIMOD was approved by the ethics committee of the Medical Board
Westfalen-Lippe and the University of M¨unster, reference number 2020-473-f-s.
This current work concerns the first five survey waves of the COVIMOD study. In
Fig 1A and B, we show the sampling periods with the number of daily COVID-19 cases,
cumulative COVID-19-related deaths, and the OxCGRT Stringency Index [19]. The
following COVID-19 policy timeline is obtained from the ACAPS COVID-19
Government Measures dataset [20]. The first COVIMOD survey was administered from
April 30
th
to May 6
th
in year 2020, towards the end of the first partial lockdown and the
first wave of cases. Before the beginning of the first survey (April 20th), small stores,
auto dealers, and bookstores were allowed to reopen under strict hygiene regulations.
During the final few days of the survey period (May 4th to 6th), phase-out measures
were announced by the government, including the step-wise uptake of schools, the
reopening of hairdressers under strict hygiene regulations, lifting of the ban on public
gatherings of 30 people indoors and 50 outdoors, resumption of religious services, and
reopening of public services such as museums, botanical gardens, zoos, and playgrounds.
The second wave of the COVIMOD survey was administered from May 14th to May
21
st
. During this period, additional phase-out measures were announced, including the
resumption of all cross-country transport and the reopening of hotels and restaurants.
International travel to neighbouring countries was also slightly relaxed during this
period. The third, fourth, and fifth waves of COVIMOD surveys were taken from May
28th to July 4th, June 11th-22nd, and June 26th to July 1st, respectively. There was no
notable introduction or reduction of social contact restriction measures during this time,
but international travel restrictions were relaxed primarily for Schengen and EU
countries. COVID-19 cases and deaths remained stable during this period (Fig 1).
After excluding participants who prefer not to provide age or gender information
and 25 participants above the age of 84, there were 1549, 1345, 1076, 1881, and 1603
participants for waves 1 to 5. We observed 3244, 4852, 6344, 13471, and 8353 total
contacts for each wave. In Fig 1C, we show the proportion of participants who
consented to the survey multiple times. Most participants in waves 2 and 3 had
participated in wave 1, with only 6.8% and 16% of participants being new to the survey.
The proportion dropped sharply in wave 4, where only 35.1% of initial participants
remained. Hence the majority (57.7%) of wave 4 participants were first-time
participants. On the contrary, no new participants were enrolled for wave 5, and
individuals who participated for the second, third, and fifth time took up approximately
45%, 10.7%, 9.6%, and 34.6% of the sample.
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