Several EU countries have accused Pfizer and AstraZeneca, the world’s leading COVID-19 vaccine manufacturers, for overpromising delivery and undermining already strained vaccine logistics, leaving national governments to seek urgent alternatives and to address growing public discontent on their own.
In the UAE, the emirate of Dubai issued a statement announcing delays in Pfizer jab inoculations due to setbacks in delivery of the lifesaving shot. The decision was made at the same time as the country issued emergency approval of Russia’s Sputnik V vaccine, adding to the UAE’s vaccine portfolio.
Given the varied production and distribution rate of different COVID-19 vaccines and the delayed inoculation marathon in countries that primarily depend on one manufacturer, many have been asking what dangers might be associated with combining multiple vaccines, while safely achieving protection against the virus.
With countries slowly diversifying their vaccine portfolio, there is also increasing curiosity about the possibility of combining vaccines based on different technologies.
If a vaccine based on dead COVID-19 virus cells is taken as the first jab, can a vaccine based on mRNA technology be taken as the second jab? Is the other way around also possible?
The answer is not so simple.
“There are no experimental data on this topic, which applies to all vaccine combinations; and there probably never will be. So, if you are relying on hard science, there’s no answer to give,” said John Moore, vaccine researcher and professor at Weill Cornell Medical College.
While combination vaccines are regularly tested in medical research, including HIV/AIDS vaccine trials, the marriage of different types of COVID-19 vaccines is marred with many questions that are unlikely to be answered in 2021.
“For many diseases, the immune response to one vaccine is not sufficient to provide a high level of protection, so the next logical step is to combine two different vaccines delivering the same antigen in a heterologous prime-boost regimen,” said Helen Fletcher, Professor of Immunology at the London School of Hygiene and Tropical Medicine to the Science Media Centre.
There is no consensus among scientists and medical practitioners on vaccine combinations.
“Combination vaccines are regularly tested in HIV trials. For example, DNA or Ad-virus or vaccinia-virus vectors followed by a subunit protein. Or combinations of vector vaccines,” added Moore. “These are trials with very careful monitoring in the initial stages. And none of them involve inactivated virus vaccines.”
Possible and safe combinations of COVID-19 vaccines
Different COVID-19 vaccines could potentially be given to people “under extreme circumstances,” according to the Public Health England (PHE), as reported by The BMJ on 4 January.
One such circumstance is if the record of the first COVID-19 vaccine dose is unknown.
“Every effort should be made to give [patients] the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all,” said Mary Ramsay, PHE Head of Immunizations, to The BMJ.
In December last year, AstraZeneca announced that it will begin testing whether the AstraZeneca/Oxford vaccine can increase efficacy in combination with Russia’s Sputnik V vaccine against COVID-19, according to the European Pharmaceutical Review (EPR).
Awaiting international approval, preliminary data on the Sputnik V vaccine showed 91.4 percent efficacy against the COVID-19 virus.
When preliminary trial results suggested Sputnik V had an efficacy above 90 percent, the Russian Direct Investment Fund, the main funder of the vaccine, along with the Gamaleya Institute, offered AstraZeneca the opportunity to use one of the two human adenoviral vector components of the Sputnik V vaccine in their clinical trials.
Both AstraZeneca/Oxford and Sputnik V are administered in two doses, but where the former uses adenoviral vectors from chimpanzees, Sputnik uses human adenoviral vectors, according to EPR.
The combination of vaccines that work on the principle of injecting dead virus cells in the human body, otherwise known as inactivated vaccines such as the Sinopharm shot, and vaccines based on the latest mRNA technology, such is the Pfizer vaccine, is an even bigger black hole.
Taking two vaccines sequentially is unlikely to be dangerous, according to Moore.
However, the issue of data remains a problem.
The UK government started allowing its citizens and residents to take one Pfizer dose, followed by one Oxford/AstraZeneca vaccine dose, under special circumstances, according to Moore.
Although they use different technology, both COVID-19 vaccines approved in the UK work to induce an immune response to the SARS-CoV-2 spike protein, according to The BMJ.
“The future is unchartered territory here,” concluded Moore.
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