As
@midlife knows:
Green Book Ch 14a
"There is no evidence on the interchangeability of the COVID-19 vaccines although studies are underway. Therefore, every effort should be made to determine which vaccine the individual received and to complete with the same vaccine. For individuals who started the schedule and who attend for vaccination at a site where the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product to complete the schedule. This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again. In these circumstances, as both the vaccines are based on the spike protein, it is likely the second dose will help to boost the response to the first dose."
DHSC
announced on 4 Feb that it has launched a clinical trial on ‘alternating’ vaccine doses, but was said to be a "13 month" trial.
JvT said last week: "Given the inevitable challenges of immunising large numbers of the population against Covid-19 and potential global supply constraints, there are definite advantages to having data that could support a more flexible immunisation programme . . . It is also even possible that by combining vaccines, the immune response could be enhanced . . . unless this is evaluated in a clinical trial we just won’t know."