German Chancellor Angela Merkel received a Moderna coronavirus vaccine as her second jab, after getting the first dose of AstraZeneca vaccine, bringing the spotlight once again on the mix-and-match of Covid-19 shots. Several medical studies are underway to determine if the process could boost immunity or make a difference in common post-vaccination symptoms. While there are still debates about the efficacy of the switching process amid a shortage of vaccines across the globe, News18 brings you a lowdown about the countries that have authorised the mixing, how safe the process is and the science behind it.
What does mixing doses mean?
Mixing vaccines could mean more than just switching manufacturers – like from Pfizer for dose one to Moderna for dose two. You might be tapping into a different way to stimulate your immune response if you opt for a first dose of AstraZeneca and a second dose of Moderna.
Researchers hope combining different vaccines will trigger a more robust, longer-lasting immune response compared to receiving both doses of a single vaccine. This approach may better protect people from emerging variants.
There is also the logistical aspect, given the shortage of Covid-19 vaccines across the world. People can get whatever shot is available without worry if the mix-and-match process is allowed.
What are the biological effects?
Scientists are of the view that since it’s the virus’s spike protein that your immune system responds to, exposure to different portions of the spike protein should mean your body will make an array of corresponding antibodies that can fend off future infection. The range of antibodies should then provide better protection and increase the likelihood that you’ll be protected from variants with changes in the spike protein.
The Pfizer and Moderna vaccines are composed of a small snippet of mRNA, genetic material that contains the recipe to make a region of the SARS-CoV-2 spike protein. Wrapped up in a fat coat, the mRNA slips into a vaccinated person’s cells where it directs production of the viral protein.
The person’s immune system then recognises the foreign spike protein and produces antibodies against it. Several other COVID-19 vaccines rely on a viral vector. In these cases, researchers modified an adenovirus that usually causes the common cold to deliver the DNA instructions for producing a portion of the SARS-CoV-2 spike protein. The modified virus is safe because it can’t replicate in people.
So far, limited data suggests an AstraZeneca shot followed by the Pfizer shot is safe and effective. The combination also appears to come with a slightly higher likelihood of temporary side effects like aches and chills.
What are the concerns?
Questions about how safe it is to mix and match, and whether the approach can prompt a better immune response, are still being answered. Even the order of mixing and matching needs to be closely studied — for example, would giving Covishield before Covaxin prompt a better immune response?
International bodies like the Coalition for Epidemic Preparedness Innovations, which is looking into mixing and matching Covid-19 vaccines, have highlighted certain complexities. These include differences in the shelf life of these vaccines, their shipment and storage conditions and contraindications — some vaccines may have more side-effects or may not work as well as others in people with specific ailments.
Studies such as the Com-COV trials show that some combinations, like AstraZeneca with Pfizer vaccines, could lead to an increase in side effects.
What do scientists say?
As governments and pharma companies all over the world prepare to bring out boosters targeting more contagious virus variants, World Health Organisation (WHO) Chief Scientist Dr. Soumya Swaminathan has said that heterologous prime-boost immunisation or immunisation using a combination of vaccines could be of big help for countries.
WHO defines heterologous prime-boost immunisation as a form of vaccination wherein two different vectors or delivery systems expressing the same or overlapping antigenic inserts are administered.
“It seems to be working well, this concept of heterologous prime-boost," Swaminathan said during a recent Zoom interview. “This opens up the opportunity for countries that have vaccinated people with one vaccine and now are waiting for the second dose they have run out of, to potentially be able to use a different platform vaccine", she said.
Director of the Vaccine Education Center at the Children’s Hospital of Philadelphia director Paul Offit was quoted as saying by Business Today that inoculating using a combination of jabs is likely to offer longer immunity or fewer side effects for certain individuals, adding basic requirement of a vaccine is to protect against hospitalisation, ICU admission and death.
What’s the global status?
Chinese researchers in April were testing the mixing of COVID-19 vaccine doses developed by CanSino Biologics and a unit of Chongqing Zhifei Biological Products, according to clinical trial registration data. Canada will recommend to mix and match a first dose of the AstraZeneca vaccine with a second shot of either Pfizer or Moderna vaccines, CBC News reported on June 1. The country’s National Advisory Committee on Immunization will also advise that recipients of a first dose of Moderna or Pfizer can get either of the two as a second shot.
France’s top health advisory body has recommended in April that people under 55 injected with AstraZeneca first, should receive a second dose with a so-called messenger RNA vaccine, although dose-mixing has not yet been evaluated in trials. Russia put on hold the approval in the country of clinical trials combining AstraZeneca and Sputnik V vaccines, after the health ministry’s ethical committee requested more data, AstraZeneca official told Reuters on May 28.
South Korea said on May 20 it would run a mix-and-match trial, mixing AstraZeneca doses with those developed by Pfizer and other drugmakers. The United Arab Emirates and Bahrain have made the Pfizer/BioNTech PFE.N, BNTX.O coronavirus vaccine available as a booster shot to those initially immunised with a vaccine developed by the China National Pharmaceutical Group (Sinopharm).
Britain said in January it would allow people to be given a different vaccine for a second dose on extremely rare occasions, for example if the first vaccine was out of stock. The first findings of an Oxford University-led study released on May 12 found that people who received Pfizer’s vaccine followed by a dose of AstraZeneca, or vice versa, were more likely to report mild or moderate common post-vaccination symptoms than if they received two doses of the same type.
In January, CNBC reported the US Centers for Disease Control and Prevention (CDC) had updated its guidance, allowing a mix of Pfizer/BioNTech’s and Moderna’s shots with a gap of at least 28 days between the two shots, and in “exceptional situations”.
Have vaccines ever been mixed before?
Mixing and matching of vaccines has been tested for decades, especially for viruses like Ebola. However, most combinations had initially been restricted to vaccines that use the same technology. In India, combinations of rotavirus vaccines have also been used and tested out.