Patients who have recently taken the Covid-19 vaccine are advised to reschedule their yearly mammogram screenings, as the presence of swollen lymph nodes - one of the known side effects of the jab - could be mistakenly identified as a sign of breast cancer. Doctors have advised patients to move their mammogram screenings to either before the Covid-19 jab or a few weeks after the second dose of the vaccine, to avoid confusion. The Pfizer-BioNTech shot can cause swollen lymph nodes in the neck or arms, though this usually gets better by itself in a week or so, says the Ministry of Health.