Mix And Match Of COVID Vaccines Could Be Dangerous, Warns WHO. Here's What Research Says

The effectiveness and full potential of the current Covid-19 vaccines are still only being studied as it is still early days to get the full picture.

Among the several experiments currently underway around the world, one of them has been much talked about - mixing two different vaccines for the two shots.

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While some early studies have suggested that mixing two COVID-19 vaccines from two different manufacturers can have provided better protection, the WHO is warning against the practice.

What WHO said

World Health Organisation (WHO) chief scientist Soumya Swaminathan has said that mixing and matching COVID-19 vaccines from different manufacturers is a "dangerous trend"?and could lead to chaos as there is limited data on it on the practice.

Addressing a COVID-19 media briefing,?Swaminathan said, "Really want to caution folks, because there is a tendency now for people in countries which enough availability of vaccines to voluntarily start thinking."

Dr Soumya Swaminathan (Image: Reuters)

"So it's a little bit of a dangerous trend here where we're in a data-free evidence-free zone as far as a mix and match there is limited data on mix and match. There are studies going on, we need to wait for that," she added.

Early studies

In May, preliminary results from the first trial in Spain involving more than 600 people show the benefits of combining different coronavirus vaccines had shown that vaccinating people with both the Oxford–AstraZeneca and Pfizer–BioNTech COVID-19 vaccines produces a potent immune response against the virus.

Starting in April, the Spanish CombivacS trial enrolled 663 people who had already received a first dose of the Oxford–AstraZeneca vaccine, which uses a harmless chimpanzee ‘adenovirus’ to deliver instructions for cells to make a SARS-CoV-2 protein.?

Reuters

Two-thirds of participants were randomly picked to receive the mRNA-based vaccine made by Pfizer, based in New York City, and BioNTech, in Mainz, Germany, at least eight weeks after their first dose. A control group of 232 people has not yet received a booster. The study was led by the Carlos III Health Institute in Madrid.

Several European countries including the UK have been seriously considering mixing Pfizer and Moderna vaccine shots as both are mRNA-based.

Others are mixing AstraZeneca and Pfizer vaccines as both produce different kinds of immune responses.

Different reasons

Some experts say mixing vaccines that target different parts of the virus can better prepare the immune system against a wider range of threats, including new variants.

In the UK, there is also a proposal for mix and match when it comes to the third, booster dose. This means that if someone has received the two doses of the?COVID-19?vaccine, they will be administered a different jab as the booster dose.

AP

Thailand said on Monday it will use?AstraZeneca Plc's COVID-19 vaccine?as a second dose for those who received Sinovac's shot as their first dose to increase protection against the disease.

The plan, if implemented, would be the first publicly announced mix and match of a Chinese vaccine and a Western-developed shot.

The country plans to also give mRNA booster shots to medical workers who received two shots of the Sinovac vaccine.

In India, too there have been some talks about mixing Covishield and COVAXIN, but it has not been implemented. Though there have been some cases of accidental mixups of the two.

Agencies

Another reason for some countries to explore the possibility of mixing two different Covid-19 vaccine shots is available.

With the delta variant spreading fast countries around the world are in a rush to vaccinate most people, but due to the shortage in supplies, many are forced to do it with whichever is available for them.

Past experience

Mixing two different vaccines is not anything new and in the past, such experiments have shown positive results.

One of the most notable such recent cases is Ebola. The Ebola vaccine developed by Johnson & Johnson is an example of an effective mixed-product vaccine in use today. It was chosen to provide long-lasting immunity. The first shot uses the same adenovirus vector as?AstraZeneca’s vaccine, and the second uses a modified version of a poxvirus called Modified vaccinia virus Ankara (MVA).

Side effects a concern

Although there is precedence for mixing vaccine types and there is a sound scientific basis for doing so, mRNA vaccines have only been approved for the first time for COVID-19.?

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This means we have no track record of what happens when used in combination with adenovirus vaccines. This is why researchers are calling for careful studies to test different vaccine combinations, paying special attention not only to their ability to boost immunity but also to any additional potential side effects.

The Oxford Vaccine Group’s Com-Cov trial analysed different vaccine combinations to test immune responses. They?found that?people who had the AstraZeneca vaccine first followed by the Pfizer-BioNTech vaccine, or the other way around, had more ‘reactogenicity’, i.e side effects such as fever, chills, headache, muscle fatigue and joint pain compared with people who had two doses of one type of vaccine.