Coronavirus: Will mixing COVID-19 vaccines provide higher immunity amid Omicron threat? Study explains

Just when we thought things are moving back to normal and settling in, COVID's Omicron variant has reignited a state of tension and chaos. Said to be highly transmissible, many believe that the variant has the potential to escape vaccine-induced immunity.

In light of such speculations then, is it right to expand the horizon and look into the possibility of mixing and matching COVID vaccines, so as to explore the chances of increased efficacy?

Read also: India’s first needle-free 3-dose coronavirus vaccine for 12+ ZyCoV-D is here: All you need to know about it

Amid discussions around the need for booster vaccines, mixing and matching of COVID-19 vaccines has been thought of as another technique to increase vaccine effectiveness.

In contrast to the 'fixed' dosing, that is two doses of the same COVID-19 vaccine brand, being administered in most countries, certain European countries have delved into the prospect of mixing vaccine doses for better efficacy.

Flexible dosing therefore means to administer the first dose from one brand of vaccine while choosing another brand of vaccine for the second dose.

New variants emerge every now and then, making it difficult for scientists to determine a way ahead. While existing COVID vaccines are said to be effective against the SARs-COV-2 virus and its variants, breakthrough cases have come to light.

Now, the new Omicron variant, which is said to be heavily mutated, is wreaking more havoc than ever. It has already impacted several countries, including India and is more rampant than any other previous strains.

Additionally, it is believed that the new variant may have developed an immune escape mechanism, helping the virus to evade vaccine-induced immunity. Having said that, many experts have said that mixing vaccine doses can trigger more robust immune responses, which is likely to provide better protection against infection.

Read also: Coronavirus: With new emerging variants, will COVID-19 booster shots become a regular affair?

Recently, in a joint statement, the European Medicines Agency (EMA) and the European Centre for Disease Prevention and Control (ECDC) said that the combination of viral vector vaccines and mRNA vaccines may provide better protection against the SARs-COV-2 virus.

According to a study involving 1070 participants, published in the Lancet, a first dose of Oxford-AstraZeneca or Pfizer-BioNTech followed by a second dose of Novavax or Moderna COVID-19 vaccines with an interval of nine weeks is said to generate a robust immune response.

Additionally, the study found that a dose of AstraZeneca vaccine (known as Covishield in India) followed by a second dose of Moderna/Novavax triggered higher antibodies and T-cell responses than getting a two-dose shot of AstraZeneca.

The study therefore promotes flexible dosing of existing vaccines and believes it to be effective.

Professor Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford, and lead author of the study, said, "Thanks to studies such as these, we are now getting a more complete picture of how different COVID-19 vaccines can be used together in the same vaccine schedule."

"Encouragingly, all these schedules generated antibody concentrations above that of the licensed and effective two dose Oxford-AstraZeneca schedule. When it comes to cellular immunity, having a first dose of the Oxford-AstraZeneca vaccine followed by any of the other study vaccines generates a particularly robust response," he further explains.

Findings from the study also suggested that most people experienced mild side effects.

Dr. Saul Faust, MD, NHS Foundation Trust in Southampton, England, and co-author of the Lancet study, says, "The side effect data show all seven vaccines are safe to use as third doses, with acceptable levels of inflammatory side effects like injection site pain, muscle soreness, fatigue."

It was found that vaccine reactions in people who received a second dose of Moderna were short lived compared to those who received two doses of either Oxford-AstraZeneca or Pfizer-BioNTech.

The first dose of AstraZeneca COVID vaccines followed by the second dose of Novavax or Moderna is believed to prove effective.

Also, a Pfizer-BioNTech/Moderna combination is believed to induce higher antibody and T-cell responses than two doses of the Pfizer jab, as per the study. The findings of the study also suggested that the combination of Pfizer-BioNTech and Novavax induced higher antibodies than two-dose Oxford-AstraZeneca vaccine dose and this schedule triggered lower antibody and T-cell responses than two-doses of the Pfizer jab.

Many experts believe initiating flexible use of existing vaccines would solve the problem of vaccine shortage in many poor and low-income countries. In light of inconsistent vaccine supply, flexible dosing may help in filling in the gaps.