New studies suggest combining doses of two different COVID-19 vaccines may be even better than repeating the same

With the changes in the AstraZeneca vaccine, new variants of the coronavirus, and supply limitations, many people are wondering if they can Mix and match vaccines against covid-19.

This means, for example, receiving the AstraZeneca vaccine as the first dose, followed by a second dose of a different vaccine, such as Pfizer’s, and boosters with other vaccines later.

Although there are many ongoing studies, data from mixed trials in Spain and the UK have recently been published.

These the data is very promising and suggest that mixed regimens may provide higher antibody levels than two doses of a single vaccine.

How does this formula work and why might it be a good idea?

The advantage of mix and match

If the covid-19 vaccination program can mix and match vaccines, greatly increases your flexibility.

Having a flexible vaccination program allows us to be agile in the face of the limitations of the global supply. If there is a vaccine shortage, instead of stopping the whole process to wait for the supply, you can continue with a different vaccine.regardless of what was given as the first dose.

If one vaccine is less effective than another against a certain variant, mixed programs could ensure that people who have already received a dose of a less effective vaccine can be boosted with a more effective vaccine against the variant.

Some countries are already using mixed immunization schedules after modifying AstraZeneca’s vaccine recommendations due to the occurrence of thrombi as a very rare side effect.

Several countries in Europe are now advising young people who previously received this vaccine as the first dose to receive an alternative vaccine as the second dose, most often mRNA vaccines like the one from Pfizer.

Spain, Germany, France, Sweden, Norway and Denmark They are among the countries that recommend mixed vaccination schedules for this reason.

It’s certain?

In a British study on the combination of vaccines published in the journal Lancet, 830 adults aged 50 and over were randomized to receive the Pfizer or AstraZeneca vaccine first, followed by the other.

People who received mixed doses were more likely to develop mild to moderate symptoms after the second dose of the vaccine, including chills, fatigue, fever, headache, joint pain, discomfort, muscle aches and pain at the injection site, compared to those who received vaccines from the same company.

However, these reactions were short lived and there were no other safety concerns. The researchers have now adapted this study to see if the early and regular use of acetaminophen reduces the frequency of these reactions.

Another similar study (not peer reviewed) from Spain found that most side effects were mild or moderate and short-lived (two to three days). They were similar to the side effects of receiving two doses of the same vaccine.

It’s effective ?

Spanish work has shown that people had a much higher antibody response two weeks after receiving the Pfizer booster, after an initial dose of AstraZeneca.

These antibodies were able to recognize and inactivate the coronavirus during laboratory tests.

This response to the Pfizer boost appears to be stronger than the response after receiving two doses of the AstraZeneca vaccine, based on previous data from the trial. The immune response to receiving the Pfizer vaccine followed by the AstraZeneca vaccine is not yet known, but the UK will have the results soon.

There is no data yet on the effectiveness of combination diets in preventing COVID-19, but they are likely to work well. The immune response is similar, if not better, compared to studies using the same vaccine as the first and second doses. This indicates that they will be effective in preventing disease.

Could you speed up vaccination programs?

In Spain, those under 60 who have received the first dose of AstraZeneca can choose to continue with the same product or receive the Pfizer vaccine. Although the Department of Health recommends a second dose of Pfizer, many have chosen to stick with AstraZeneca.

Recent real-world findings in the UK suggest that after two doses both vaccines are equally effective against the variants circulating in the British Isles.

The recommendations on changing the vaccine in different countries are due to concerns about the appearance of thrombi after the first dose of AstraZeneca, as well as the changing age groups of citizens receiving it and supply issues.

This led to widespread uncertainty and meant that young people in some European countries who had already received a first dose were excluded from receiving a second dose.

The results of these mixed studies support the possibility of vaccinating those who received the first dose of AstraZeneca with a different booster, if the need arises.

Are in class continue research to assess mix and match schedules with Moderna and Novavax vaccines.

Do not delay getting vaccinated

While in some countries cases are decreasing, many others are seeing an increase. Among them are Taiwan and Singapore, which were previously hailed as excellent examples of handling COVID-19.

These examples demonstrate the difficulty of lasting suppression of the virus in the absence of high vaccination coverage. This will be exacerbated by the newer, more transmissible variants.

Current cases in many parts of Europe, the United States and Australia are caused by variant B.1.617.1 (“India”). Both vaccines are effective against the closely related B.1.617.2 variant to India (although slightly less than against B.1.1.7), and similar efficacy would be expected against B.1.617.1.

In the meantime, it is essential that people do not delay their vaccination with the product offered to them. Vaccination is an essential part of the strategy to exit the pandemic.

The vaccination schedule is likely to change in the future, as boosters may be needed. This is normal in vaccination programs. We already do this every year with the flu shot. This should not be seen as a political failure, but rather as an evidence-based response to new information.

Fiona Russell is an infectious disease epidemiologist and senior researcher at the University of Melbourne

John Hart is a clinical researcher at the Murdoch Institute for Research in Children

Originally posted in The Conversation

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