We combined a natural experiment (the occurrence of the COVID-19 pandemic in 2020) with the tools of laboratory experiments to study whether and how an unprecedented shock on social interactions (the introduction and abrogation of a nationwide lockdown) affected the evolution of individuals' social preferences, and willingness to trust others. In a longitudinal online incentivized experiment during the first lockdown in France, we elicited the same participants' preferences for prosociality, trust and trustworthiness every week for three months. Despite the exposure to long-lasting social distancing, prosocial preferences and the willingness to reciprocate the trust of others remained stable during the whole period under study. In contrast, the lockdown had an immediate negative effect on trust, which remained at lower levels til after the lifting of such measures but recovered its initial level nine months later. The decline in trust was mainly driven by individuals who experienced financial hardship, a lack of outward exposure, and higher anxiety during the lockdown.