It is important people receiving immunosuppressive therapy are provided with the best protection against COVID-19 because they are at greater risk of severe illness should they become infected. As severe immunosuppression can reduce the efficacy of COVID-19 vaccination, doctors agree that COVID-19 boosters is are important to maximise the vaccine response in these people. However, we don't currently know the best time to give booster vaccines to people about to start immunosuppressive therapy. This research aims to address this knowledge gap by examining whether the greatest protection is provided by giving the COVID-19 booster just before the immunosuppressive therapy starts or by waiting and giving the booster 6 months after treatment start. At the 6-month timepoint, in many cases the more intensive immunosuppression is often weaning and the immune system is starting to rebuild.
Inclusion Criteria: * Adult aged at least 18 years * Previously vaccinated with 2 (or more) doses of any licensed COVID-19 vaccine who requires initiation of moderate-to-severe immunosuppression; most recent COVID-19 vaccine dose must have been given \> 3 months prior * Planned significant immunosuppressive therapy for at least 1 year * No cyclophosphamide, alemtuzumab or rituximab treatment in the past 5 years. Note: patient may have concurrent steroids with any treatments listed in protocol * Voluntarily given written informed consent Exclusion Criteria: * Pregnant or breastfeeding * Has underlying primary immunodeficiency * Has received or likely to receive intravenous/subcutaneous immunoglobulin (IVIg/ScIg). * Projected treatment is likely to involve plasma exchange * Contraindication to receipt of SARS-CoV-2 vaccine * Intolerance of or previous allergic reaction to tetanus vaccination * Patients switching immunosuppressive therapies following enrolment with an absolute lymphocyte count \<0.5 x 109/L immediately prior to screening