Table 3.

Risk of bias in included studies assessed by the ROBINS-I tool

Risk-of-bias domains
Study, year	Confounding	Selection of participants	Classification of interventions	Deviations from intended intervention	Missing data	Measurement of outcomes	Overall risk of bias	Selection of reported result
Vaccination before SARS-CoV-2 infection
Al-Aly 202219	Low	Low	Low	Low	Low	Moderate	Low	Moderate
Antonelli 202220	Moderate	Low	Low	Low	Serious	Serious	Low	Serious
Ayoubkhani 202221	Critical	Low	Low	Low	Moderate	Low	Low	Critical
Azzolini 202222	Moderate	Low	Moderate	Low	NI	Critical	Low	Critical
Ioannou 202223	Moderate	Low	Low	Low	NI	Low	Moderate	Moderate
Mohr 202224	Serious	Serious	Low	Low	Serious	Moderate	Moderate	Serious
Pell 202225	Serious	Low	Serious	Low	Serious	Moderate	Moderate	Serious
Tannous 202226	Serious	Low	Low	Low	Low	Serious	NI	Serious
Taquet 202127	Moderate	Low	Low	Low	NI	Low	Low	Moderate
van der Maaden 202228	Serious	Low	Moderate	Low	Low	Low	Low	Serious
Zisis 202229	Serious	Critical	Serious	Low	NI	Serious	NI	Critical
Vaccination after SARS-CoV-2 infection or after diagnosis of long covid
Ayoubkhani 202230	Low	Low	Low	Low	Moderate	Low	Low	Moderate
Simon 202131	Serious	Low	Low	Low	Moderate	Low	Low	Serious
Tran 202132	Moderate	Low	Low	Low	Low	Low	Low	Moderate
Wisnivesky 202233	Serious	Serious	Serious	Low	Low	Low	Low	Serious
Wynberg 202234	Serious	Moderate	Serious	Low	Low	Serious	Low	Serious

NI=no information.