<span style="color: #222222;">Britain launched a trial to assess the immune responses generated if doses of the COVID-19 vaccines from Pfizer Inc. and AstraZeneca Pharmaceuticals are combined in a two-shot schedule. The British researchers behind the trial said data on vaccinating people with the two different types of Corona virus vaccines could help understanding of whether shots can be rolled out with greater flexibility around the world. Initial data on immune responses is expected to be generated around June.</span><br />'' <span style="color: #222222;"> </span><br />'' <span style="color: #222222;">The trial will examine the immune responses of an initial dose of Pfizer vaccine followed by a booster of AstraZeneca's, as well as vice versa, with intervals of four and 12 weeks.</span><br />'' <span style="color: #222222;"> </span><br />'' <span style="color: #222222;">Recruitment for the study starts on Thursday, with over 800 participants expected to take part, the researchers said. That makes it much smaller than the clinical trials that have been used to determine efficacy of the vaccines individually.</span><br />'' <span style="color: #222222;"> </span><br />'' <span style="color: #222222;">The trial is looking to recruit people over the age of 50 who may be at higher risk than younger people and have not been vaccinated already.</span><br />'' <span style="color: #222222;"> </span><br />'' <span style="color: #222222;">AstraZeneca's shot is also being tested in combination with Russia's Sputnik V vaccine and British drug maker's research chief has said more studies on combining vaccines should be done.</span>