Doctors say COVID vaccine mixing could be in our future as trials begin in US and UK

SAN FRANCISCO -- As more people are getting vaccinated, medical experts in the United Kingdom and the U.S are holding trials to find out if giving two doses of a different COVID vaccine improves your immune response.

Scientists have been combining or mixing vaccines in the past with several diseases like Malaria, TB and Influenza. Mixing COVID-19 vaccines is a new concept that has not been approved by the CDC, but experts say that could change in the future.

More than 800 people in the UK are part of a trial where they are getting injected with one dose of the Pfizer vaccine and 28 days later with a dose of the AstraZeneca vaccine instead of a Pfizer shot for a second shot.

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"There is absolutely a possibility, and I think it's quite an exciting possibility that if you combine these two different vaccines you can broaden that immune response. You can strengthen that immune response," said Helen Fletcher, BSc Ph.D., Professor of Immunology at London School of Hygiene and Tropical medicine.

Dr. Fletcher says using two different vaccines could also help logistically with vaccine distribution.

Luz Pena: "Are there any dangers in mixing vaccines?"
Dr. Helen Fletcher: "No there is not. So, I went back into the history of the scientific literature looking for reports of mixing and matching vaccines to see if there were any concerns. There is no additional concern through mixing vaccines."

In April, Mountain View resident Veena Thomas got the Pfizer vaccine as her first dose and by mistake the nurse injected her with a dose of the Moderna vaccine.

"I did get side effects, but I think they were the same as everybody else," said Thomas.

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Stanford immunologist, Dr. Bali Pulendran says mixing vaccines could be the key to save lives in hard-hit places like India.

"I'm afraid that mixing and matching might become a necessity just because there is no guarantee that people in these parts of the world will be able to get two doses of the vaccine from a single manufacturer," said Dr. Pulendran.

Dr. Pulendran says there are two driving forces that could lead to COVID-19 vaccine mixing. One is a necessity the other is an immunological benefit.

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"That is why from a regulatory perspective. Strictly speaking, any combination of two vaccines should be first tested in a clinical trial. The purpose of doing that will be to make sure that this combination is safe and the benefits they bring far outweigh the potential safety concerns," said Dr. Pulendran

Gritstone Bio is already manufacturing a vaccine combination. Dr. Andrew Allen, who Co-founded Gritstone Oncology, Inc says this year they launched a second-generation COVID vaccine program. The phase 1 clinical trial is currently being run by National Institute of Allergy and Infectious Diseases.

"We are trying to figure out what the right cocktail is. What is the best combination? The best dose, the best interval between dose one and dose two," said Dr. Allen.

Luz Pena: "Which vaccines are you actively mixing right now?"
Dr. Andrew Allen: "We use the adenovirus as the prime typically and then we boost with the RNA based vaccine," and added, "If you want to get the best of both worlds the merging evidence suggest that the adenovirus is the best at driving the T-Cell response and the RNA is better at driving the antibody-based response. That is why combining them may give you the best outcome."

Dr. Allen says patients who have bad antibody systems could potentially benefit more from their vaccine.

"Patients for example who have MS who may have been treated with one of the new effective therapies for MS that basically gets rid for antibodies," and Dr. Allen added, "There are many cancer patients who have a similar problem that are solid organ transplant patients who received various drugs that also suppressed the immune system. These groups of patients are not probably getting great protection from the first generation vaccines. That is a group for example were mix and matching and driving the T-cell side may lead to a better outcome."

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