Shot of knowledge

Mix-and-matching vaccines is a life-saving cocktail, says new report

Swedish study casts even darker shadow over SA’s sale of the AstraZeneca vaccine

18 October 2021 - 13:55
If we had switched from AZ to Pfizer for the second dose, thousands more lives could have been saved.
SHOT IN THE ARM If we had switched from AZ to Pfizer for the second dose, thousands more lives could have been saved.
Image: REUTERS/Dado Ruvic

The ghost of the AstraZeneca controversy will haunt SA for some time, and it’s become more relevant as research suggests one dose of AZ followed by a second dose of an mRNA vaccine such as Pfizer is even more potent than two doses of AZ.

The research paper, just published in The Lancet Regional Health — Europe, has major implications for vaccine policies around the world.

It tells us, with hindsight, if SA had rolled out the first doses of AstraZeneca instead of selling them, and had then switched to the Pfizer vaccine which is now so readily available, thousands of lives could have been saved.

Our study shows a greater risk reduction for people who received an mRNA vaccine after having received a first dose of a vector-based vaccine, compared to people having received the vector-based vaccine for both doses.
Peter Nordström, professor of geriatric medicine at Umeå University.

The mix-and-match success was shown in a nationwide study conducted by researchers at Umeå University in Sweden.

“Having received any of the approved vaccines is better compared to no vaccine, and two doses are better than one,” says Peter Nordström, professor of geriatric medicine at Umeå University. 

“Our study shows a greater risk reduction for people who received an mRNA vaccine after having received a first dose of a vector-based vaccine, compared to people having received the vector-based vaccine for both doses.”

Since the use of Oxford-AstraZeneca’s vector-based vaccine against Covid was halted for people younger than 65, all individuals who had already received their first dose of this vaccine were recommended an mRNA vaccine as their second dose.

During a two-and-a-half-month average follow-up period after the second dose, the study showed a 67% lower risk of infection for the combination of AstraZeneca and Pfizer, and a 79% lower risk for AstraZeneca and Moderna, both compared to unvaccinated individuals. 

For people having received two doses of the Oxford-AstraZeneca vaccine, the risk reduction was 50%. 

These risk estimates were observed after accounting for differences regarding date of vaccination, age of the participants, socioeconomic status and other risk factors for Covid.

“Importantly, the estimates of effectiveness apply to infection with the Delta variant, which was dominating the confirmed cases during the follow-up period,” say the researchers.

Previous research has demonstrated that mix-and-match vaccine schedules generate a robust immune response — but the full extent of this was unclear.

“This is the knowledge gap which the new study aimed to fill,” say the researchers who included about 700,000 individuals in the study.

“The results of the study may have implications for vaccination strategies in different countries,” says Marcel Ballin, a doctoral student in geriatric medicine at Umeå University and co-author of the study.  

“The World Health Organisation has stated that despite the promising results from previous studies regarding immune response from mix-and-match vaccination, there is a need to investigate their safety and effectiveness against clinical outcomes. Here we now have one such study.”

But even before this latest research, vaccinology expert Prof Shabir Madhi from Wits University said that the lives of 18,000 to 22,000 elderly South Africans could have been saved had the country not sold 1.5-million doses of the AstraZeneca vaccine to other African countries in March

The sale also fuelled vaccine hesitancy across the continent, leaving many doses unused until they expired.

This is according to Madhi’s in-depth analysis and conclusion that the government “completely ignored” the advice of the WHO — with disastrous consequences.

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