Vaccination prepares the body’s immune system ready to recognise, destroy and remember foreign disease-causing agents when it encounters them. It is the most effective way of averting communicable diseases if fully accepted and demanded by the population at risk of spreading contagious diseases. Social mobilisation has been a critical way of encouraging demands, as well as acceptance and compliance, by the general public for immunisation services. Vaccination campaign against poliovirus by WHO since 1988 was a huge success across the globe except in three countries: Nigeria, Afghanistan and Pakistan. Up until 3 years ago, polio eradication remained a challenge in Nigeria due mainly to non-acceptance of the vaccination by the hard-to-reach (HtoR) group. In this study, carried out at the height of the epidemic in Nigeria, we investigated the effects that social mobilisation on polio vaccination had on the hard-to-reach group. The participants were selected based on three criteria: age of the child, religion and social status. Semi-structured interview was employed and data analysed using the thematic content analysis. The results revealed that religion, service factor-distance to health facility and health staff behaviour are the key factors limiting the social mobilisation effort among the HtoR group. Nigeria began to make success only when one of the most respected Muslim leaders took ownership of the campaign for the elimination of polio, which has now placed Nigeria among the polio-free countries. Therefore, effective social mobilisation for vaccination programs of the HtoR group could be achieved faster with the involvement of religious leaders because of the enormous influence they have on their followers. This revelation is very important to note for the success of the upcoming vaccination campaign against COVID-19 disease, now that effective vaccines against the disease have been developed and ready for distribution. Keywords: Poliovirus, COVID-19, vaccination, social mobilisation, hard-to-reach population.