AstraZeneca + Pfizer vaccines = better omicron immunity
A health care worker prepares to administer the Pfizer COVID-19 vaccine. Credit: AP/Matt Rourke
Could the United Kingdom inadvertently have given some of its population the best immunity possible against SARS-CoV-2?
After reported side effects among some populations with the AstraZeneca vaccine, the UK and much of Europe decided to use Pfizer shots as a second shot in certain age groups, creating a natural mix-and-match dosing experiment. New data from the UK suggests that this particular mix offered extra immunity from the omicron variant compared with those who had other platforms.
In many ways, that's not surprising. Researchers have known for years that mixing and matching vaccines can produce stronger or longer-lasting immunity and also provide a greater defense against variants. What they didn't know was how mixing the various vaccine platforms would affect immunity to SARS-CoV-2 and serious disease.
A health care worker prepares a dose of the AstraZeneca COVID-19 vaccine. Credit: AP/Juan Karita
Given the latest scientific data, we should spend a lot more effort studying such effects. Below, Therese speaks with Bloomberg Intelligence senior pharmaceutical analyst Sam Fazeli about the new data on mix-and-match dosing.
The RBD of the spike protein is the part which first engages with a human cell and "binds" to its receptor, the human ACE-2 molecule. Without this binding, no infection would occur. Antibodies that interfere with this binding "neutralize" the virus. It is therefore this region where most of the mutations occur in the virus to get around our protective antibodies.
So if most of your memory B-cells target this region, an infection may take longer to resolve or have a higher chance to lead to more severe disease because the virus mutates the RBD and escapes the antibodies. In the mix-and-match group, there were more non-RBD antibodies.
But clearly for any of these shots to be effective, people need to take them and get their boosters. What we do know about the latest South African wave is that it was short-lived and had even lower morbidity/mortality per infection than the omicron BA.1 wave.
What we really need to do is look at whether using a different vaccine platform would give us longer and better immunity than repeatedly going to mRNA shots.
The side effect issues with both the adenoviral vaccines are much better understood and there are even proposed modifications that may reduce them significantly. But for this to be studied, government-funded institutions may need to get involved as the manufacturers have essentially stopped investing in them.
