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Use of two different Covid vaccines effective and safe, preliminary research finds

The THL's chief physician noted that it does not appear that combining AstraZeneca with an mRNA vaccine causes more side effects than using the same vaccine product for both doses.

Pfizer-rokotetta valmistava sairaanhoitajat Vantaan Energia Areena rokotuskeskuksessa. 26.5.2021.
A dose of the Pfizer Covid-19 vaccine being extracted from a vial by a health care worker at a vaccination site in Vantaa. Image: Jorge Gonzalez / Yle

According to preliminary research, the combined use of adenovirus vector vaccines and mRNA vaccines is effective, the Institute for Health and Welfare (THL) reported on Wednesday.

This means that people who received the AstraZeneca Covid vaccine as their first dose can safely take an mRNA vaccine — like the one manufactured by Pfizer — as their second.

As the end of March approached, around 100,000 individuals in Finland — mainly people belonging to medical risk groups — had already received an AstraZeneca jab before news of rare blood clot side effects emerged.

In May, Finland began recommending that people under the age of 65 who received a first dose of AstraZeneca's coronavirus vector-based vaccine to have their second shot be an mRNA-based vaccine.

Following a suspension of administering AstraZeneca to anyone, the THL then approved the resumption of its use in people over the age of 65.

Results still preliminary

On Wednesday, THL said that early studies in Germany, Spain and the UK found that the combination of the two vaccine types were effective and did not raise safety concerns.

However, the institute noted, the results of the studies were still preliminary and had not yet undergone scientific peer reviews.

THL said that pairing the two vaccine types can provide at least as good an immune response to coronavirus infections as those who received two of the same types of jabs.

"These results support our previous assessment that the administration of two different vaccine products is both a safe and a good protective option," THL's chief physician Hanna Nohynek said in a statement.

"It was previously suspected that combining vaccine products could produce more transient side effects like fever and muscle pain than when the same vaccine product was given. The results of the current study do not support this suspicion, as those who received two different products have not experienced significantly more adverse effects than those who received one product," she continued.

As of Wednesday, 48.3 percent of Finland's population had received at least one dose of a Covid-19 vaccine, or nearly 2.7 million people, according to THL data.

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