AS countries around the world grapple with the constrained supply of vaccines for Covid-19, the possibility of getting people vaccinated more quickly if vaccines can be mixed and matched has been raised.
In fact, in the United Kingdom, a controversial trial to mix and match the first and second doses of different vaccines with the Moderna and Novavax shots is currently underway in an attempt to find out if such a strategy might offer better and longer-lasting immunity against the virus and its new variants, and also allow more flexibility in the rollout.
But experts argue that by using two different vaccines, there is not going to be a greater magnitude of protection against the disease.
While the Pfizer-BioNTech, Moderna, and Johnson & Johnson vaccines do offer a degree of protection against Covid-19, we are seeing variant strains, and expectations of the vaccine protecting people from the disease could decrease. Clinical trials will be warranted to prove this, however.
It is important to note that, according to the most current guidelines from the Centres for Disease Control and Prevention (CDC), lack of available safety data means Covid-19 vaccines shouldn’t be mixed unless there’s an exceptional situation, like an acute shortage of the first vaccine that the person received.
As I understand from my undergraduate studies in Microbiology, the AstraZeneca and Pfizer-BioNTech vaccines use two different technologies. The Pfizer-BioNTech vaccine is an mRNA vaccine whereas AstraZeneca’s uses the adenovirus vector technology, which is similar to the Johnson & Johnson vaccine. Both vaccines contain instructions that tell our cells to make the spike protein of SARS-CoV-2, the virus that causes Covid-19.
This causes our bodies to build an immune response against the coronavirus spike protein, which helps to protect us if we are exposed to the virus. The difference is how the two vaccines transport these instructions to our cells.
Pfizer uses mRNA coated in lipid (fatty) material to get the information into the cells while AstraZeneca uses a weakened version of an adenovirus, a common cold virus, to do the same thing. Both vaccines currently require two doses.
Ideally, one would need the second dose to achieve 90% efficacy. However, in dire circumstances such as a shortage of vaccines, it would be better to get more people vaccinated with a single dose. At least some protection is better than none.
As for mixing and matching vaccines, there’s simply too little known about it currently, hence I personally am not up for it.
R. MURALI RAJARATENAM