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Coronavirus

Is it safe to mix-and-match COVID-19 vaccines? Here’s what we know so far

Published: Updated:

With COVID-19 vaccine programs underway in most parts of the world, some countries are considering combining vaccines, where one vaccine is administered to the individual as the first shot and another vaccine type as a second shot several weeks later.

The question that has been on many peoples’ minds is: how safe is it to be combining COVID-19 vaccines from different manufacturers?

Read the latest updates in our dedicated coronavirus section.

According to the global vaccine alliance GAVI, it could be a good idea to do so, for a number of reasons.

Vaccine supply issues: shortages and delays

Some countries are experiencing vaccine supply shortages and delays, just months after receiving their first shipments. Earlier this year, international vaccine-sharing program COVAX supplied several developing countries with vaccines, but many of them are now facing shortages and are unsure about the timeline for wealthier nations to donate vaccines to them.

On Monday, a representative from the World Health Organization (WHO) said that 40 of the 80 countries that received vaccines through the COVAX program were either out or on the verge of running out of shots.

“Well over half of countries have run out of stock and are calling for additional vaccines. But in reality, it’s probably much higher,” WHO advisor Bruce Aylward said at a briefing on Monday.

COVAX has so far distributed 90 million doses, the BBC reported on Monday, which is nowhere near enough to protect vulnerable populations against COVID-19. Trinidad and Tobago, Bangladesh, Uganda and Zimbabwe have all run out of vaccines recently.

A nurse prepares to administer the AstraZeneca/Oxford vaccine under the COVAX scheme against the coronavirus disease (COVID-19) at the Eka Kotebe General Hospital in Addis Ababa, Ethiopia March 13, 2021. (File Photo: Reuters)
A nurse prepares to administer the AstraZeneca/Oxford vaccine under the COVAX scheme against the coronavirus disease (COVID-19) at the Eka Kotebe General Hospital in Addis Ababa, Ethiopia March 13, 2021. (File Photo: Reuters)

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Over the past few months, widespread vaccinations have made managing the pandemic a lot easier. Slowdowns in inoculation campaigns can increase virus transmission which can lead to the emergence of new, and more infectious variants making the viruses spread more difficult to control.

Al Arabiya English spoke with the Internal Medicine Specialist at Bareen International Hospital in the United Arab Emirates, Dr. Azeem Abdul Salam Mohamad, who echoed this sentiment.

“The most obvious benefit of the approach of mixing up vaccine shots is logistical in nature. People can complete vaccination by whatever vaccine is available, without the need to worry,” he said.

Efficacy of vaccine mixing

Many countries have now approved the mixing of COVID-19 vaccine doses. South Korea recently decided to offer the Pfizer vaccine as a second shot to those who received their first dose of the AstraZeneca jab. This was mainly due to shipment delays. Similarly, Abu Dhabi recently approved the Pfizer jab as a third/booster shot for those who were given the Sinopharm vaccine.

“A Spanish study [Combivac] found that giving a dose of Pfizer shot to individuals who already received the AstraZeneca vaccine is highly safe and effective,” said Dr. Mohamad. “Combining different vaccines will trigger a more robust, longer-lasting immune response which may better protect people from emerging variants.”

Healthcare workers prepare doses of the Moderna coronavirus disease (COVID-19) vaccine before administering them to staffers of Japan's supermarket group Aeon at the company's shopping mall in Chiba, Japan June 21, 2021. (Reuters)
Healthcare workers prepare doses of the Moderna coronavirus disease (COVID-19) vaccine before administering them to staffers of Japan's supermarket group Aeon at the company's shopping mall in Chiba, Japan June 21, 2021. (Reuters)

“The bottom line is that we need more research to determine whether using different vaccines in a patient will work or not. Obviously, it would provide logistical benefit if vaccination programs could use whatever vaccines are available if a limited supply keeps the patient from receiving their second dose of the same vaccine as the first,” Chief Health Officer at Project HOPE and former Director of Global Health at the US Centers For Disease Control & Prevention (CDC) Dr. Tom Kenyon told Al Arabiya English.

“Some countries allow a Pfizer vaccine to be followed by Moderna or vice versa, but those are both mRNA vaccines. There is a theoretical possibility that using different vaccines could actually strengthen the immune response to different parts of the spike protein, but we need to await further study results before allowing mixing vaccine doses.”

Minor side effects noted when combining different vaccines were fever and body pain, according to Dubai-based specialist Dr. Mohamad, symptoms which are already known from taking the vaccine.

There has been some compelling preliminary evidence suggesting that mixing vaccine shots from different manufacturers could lead to a stronger immune response compared to two doses of the same vaccine, a statement by GAVI read.

According to the global vaccine alliance program, a study is currently underway to test the efficacy of mixing the AstraZeneca jab as the first shot and Russia’s Sputnik V vaccine as the second. Both of the vaccines use an adenovirus - one of the causes of the common cold- as a delivery system to build immunity against COVID-19. The results are yet to be published.

“Besides the potentially positive impact on the immune system, another possible added bonus of mixing vaccines could be to prevent vaccines from being rendered less effective in the face of new variants,” the GAVI statement read. “As the virus mutates the part of it that a vaccine targets could change, which could make the vaccine less effective. But if two vaccines target different parts of the virus, it gives our immune system more than one weapon in its arsenal.”

“The Combivac Spanish trial between the AstraZeneca vaccine as the first dose and Pfizer as the second which was tested on around 663 people, proved to boost immunity,” UAE-based Pulmonologist at Medcare hospital Sharjah Dr. Mohammed Harriss told Al Arabiya.

Side effects

While mixing different vaccine types has proven to be somewhat effective, researchers and experts have been calling for careful studies when it comes to testing vaccine combos, urging closer attention to not only their ability to boost immunity but the severity and volume of additional side effects that could be brought on as a consequence, according to GAVI.

Earlier this month, the Oxford Vaccine Group’s Com-Cov trial, which analyzed vaccine combinations, found that people who were given the AstraZeneca jab followed by the Pfizer-BioNTech shot, and vice versa, had more side effects compared to people who took two doses of the same exact vaccine. These included headaches, fever, chills, and body pain in the joints and muscles.

The group noted that none of the participants needed to be hospitalized because the symptoms did not last for long however, the data on this research is particularly limited as only people aged 50 and over were tested. They noted that this might mean that vaccine combos could be more severe in younger people.

“With repeated vaccinations of the same-virus based vaccines, including the AstraZeneca and the Sinopharm, the efficacy may decrease because the immunological system recognizes the type of virus being used to build immunity, so the immunity might be less. So when you give another category of vaccine, mRNA like Pfizer and Moderna, the efficacy will get boosted but there are side effect concerns such as fever, chills and body pain but they are definitely controllable,” said Dr. Harriss.

“I do believe it’s logical to mix vaccine types because COVID-19 is not like any other simple virus. So in future, we definitely need to develop and follow a strategy that focuses on how we can boost immunity and modify the immune response to combat future variants of the virus.”

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