Appendix 2—table 2. Summary of the model parameters.

Symbol	Interpretation	Value(s)	References
SARS-CoV-2 infection parameters:
${\displaystyle {\beta }_C}$	transmission rate of SARS-CoV-2	0.46 days–1	Liu et al., 2020
${\displaystyle {\gamma }^c}$	SARS-CoV-2 recovery rate (mild cases)	1/7 days–1	Lauer et al., 2020; Rhee et al., 2020
${\displaystyle ϵ}$	SARS-CoV-2 incubation rate (latent period from exposed to infectious state)	1/5 days–1	Elias et al., 2021
${\displaystyle {\theta }_c}$	Relative risk of SARS-CoV-2 transmission due to lockdown implementation	0.23	Salje et al., 2020
Pneumococcal colonization and invasion parameters:
${\displaystyle {\beta }_s}$	transmission rate of antibiotic-sensitive strain	0.056 days–1 0.046 days–1 0.034 days–1	Davies et al., 2019; Olesen et al., 2020
${\displaystyle f}$	fitness of antibiotic-resistant strain (assuming there is a fitness cost on transmissibility)	0.9652 0.949 0.926	Dagan et al., 2008; Melnyk et al., 2015
${\displaystyle {\beta }_{s}f}$	transmission rate of antibiotic-resistant strain		calculated
${\displaystyle {\theta }_{\beta }}$	Relative risk of pneumococcal transmission due to lockdown implementation	1 or 0.75	assumed
${\displaystyle \begin{array}{c}{\gamma }^S={\gamma }^R={\gamma }^{SS}\\ ={\gamma }^{RR}={\gamma }^{SR}\end{array}}$	rate of natural bacterial clearance (assumed to be the same for antibiotic-sensitive and -resistant strains)	1/20 days–1 1/30 days–1 1/45 days–1	Abdullahi et al., 2012; Davies et al., 2019; Ekdahl et al., 1997; Högberg et al., 2021,Melegaro et al., 2004
${\displaystyle q}$	relative infectiousness with each strain for dually colonized	0.5	assumedColijn et al., 2010
${\displaystyle c}$	fraction of dually colonized returning to single-colonized upon reinfection	0.5	assumed (Colijn et al., 2010)
${\displaystyle r}$	probability of acquiring secondary bacterial carriage	0.5	assumed (Colijn et al., 2010)
${\displaystyle p_s}$	probability of transmitting antibiotic-sensitive strain	0.5	assumed (Colijn et al., 2010)
${\displaystyle p_{single}}$	probability of a single infection	0.5	assumed (Colijn et al., 2010)
${\displaystyle p_{inv}}$	pneumococcal invasion rate (summer and winter)	[3x10-6 day–1,9x10-6 day–1] in the elderly and general population, and [1x10-6 day–1, 2.5x10-6 day–1] in <5 years-old	Domenech de Cellès et al., 2019; Opatowski et al., 2013
${\displaystyle S^S+S^R}$	initial states – initial prevalence of the total pneumococcal carriage (antibiotic-sensitive and -resistant) in different populations	10% 20% 30%	Cohen et al., 2023; Rose et al., 2021; Rybak et al., 2022; Tinggaard et al., 2023; Wang et al., 2017
Antibiotic exposure parameters:
${\displaystyle \omega }$	rate of antibiotic-induced pneumococcal clearance for sensitive strains(1/time before antibiotic action)	1/3 days–1	Kuitunen et al., 2023
${\displaystyle r}$	rate of return to antibiotic unexposed compartment (1/duration of antibiotic treatment)	1/7 days–1	Grant and Saux, 2021; Kuitunen et al., 2023
${\displaystyle r_{az}}$	rate of return to antibiotic unexposed compartment (1/the remainder of how long azithromycin stays in the body)	1/11.5 days–1	calculated (Foulds et al., 1990; Girard et al., 2005)
${\displaystyle \tau }$	baseline rate of antibiotic exposure in the community (France)	0.0014 average daily ppc (prescriptions per capita)	Bara et al., 2022
${\displaystyle a}$	A reduction factor for antibiotic exposure in the community resulting from changes in healthcare-seeking behavior in response to the COVID-19 pandemic	[0.51, 0.77, 0.84]to represent annual 13%, 18%, and 39% decrease observed in France	Bara et al., 2022
${\displaystyle p_{az}}$	A proportion of COVID-19 infected individuals in the community receiving azithromycin	[0–0.20]testing between 0% and 20%	Tsay et al., 2022; Wittman et al., 2023
Pathogenicity (invasive pneumococcal disease risk):
${\displaystyle IP{D}_{risk}}$	A reduction factor for the risk of developing an invasive pneumococcal disease (IPD) due to the absence of influenza-like-illnesses (ILIs) after lockdown implementation	1 (pre-lockdown) 0.2 (lockdown) 0.4 (post-lockdown) for an average of 0.5 in 2020	Shaw et al., 2023