Covid-19 vaccines: Mix and match




Chile Health Ministry




Should you mix and match Covid-19 vaccines for your booster shot?

Amrita Kaur

  • PublishedNov 9, 2021, 4:30 pm SGT


SINGAPORE – Planning to get your booster shot against Covid-19 and wondering whether to mix vaccines?

On Monday (Nov 8), the Ministry of Health’s director of medical services Kenneth Mak assured the public that taking a different mRNA vaccine as a booster shot is “perfectly safe”.

Associate Professor Mak revealed that he had taken the Moderna vaccine for his booster jab to add to his two doses of the Pfizer BioNTech/Comirnaty vaccine, partly out of convenience. At the same multi-ministerial task force on Covid-19 press conference, Health Minister Ong Ye Kung said he, too, had taken Moderna as a booster after earlier Pfizer BioNTech/Comirnaty jabs.

A study in the United States had found that taking Moderna as a booster resulted in higher levels of antibodies, which is one indication of greater protection.

The study by the National Institutes of Health (NIH), which is preliminary and yet to be peer-reviewed, evaluated how 458 people vaccinated with Moderna, Pfizer or Johnson & Johnson reacted to a booster dose of the same shot or a new one.

Those who had taken the Moderna vaccine for the first two doses and the Moderna booster were found to have the highest antibody levels. Those who got two doses of Pfizer, followed by a Moderna booster, had the second highest antibody count. Next were those who got two doses of Moderna, followed by a Pfizer booster.

But Singapore doctors tell The Straits Times that there is little difference in choosing either mRNA vaccine – Moderna and Pfizer BioNTech/Comirnaty – as both have comparable efficacy as boosters.

Citing the NIH study, Dr Alvin Neo, head of clinical projects at clinic chain Northeast Medical Group, says there is evidence of comparable efficacy and immunogenicity with either Pfizer BioNTech/Comirnaty and Moderna vaccines as boosters.

Immunogenicity refers to the ability of cells or tissues to produce an immune response.

Dr Neo says: “The increase in immune response with the different mRNA vaccines is not very significant and may not represent a significant incremental protection rate.”

Other than those who choose to mix mRNA vaccines, some opt for a non-mRNA vaccine like Sinovac or Sinopharm as a booster as they had undesirable side effects from mRNA inoculations.

On whether one should play it safe and stick to the same vaccine for one’s booster jab, Prof Hsu says: “We have more than sufficient evidence of safety for the booster shots. And while adverse effects such as arm pain, fatigue and fever are to be expected, it is more a personal preference as to whether one should stick to the same vaccine or switch to a different one.”


  • 21 October 2021

Mix-and-match COVID vaccines ace the effectiveness test

Combining two different COVID-19 vaccines provides protection on par with that of mRNA vaccines — including protection against the Delta variant.

tudy after study has shown that people who receive two different COVID-19 vaccines generate potent immune responses, with side effects no worse than those caused by standard regimens.

But now, for the first time, researchers have shown that such ‘mix and match’ regimens are highly effective at preventing COVID-19 — roughly matching or even exceeding the performance of mRNA vaccines.

The high antibody levels and other strong immune responses elicited by mix-and-match regimens suggested they would offer good protection against disease. Still, “I was delighted to see that it’s as effective as one would expect,” says immunologist Martina Sester at Saarland University in Homburg, Germany. “This is really good news and this will certainly have influence on clinical practice.”

“These emerging effectiveness data support the use of these approved COVID-19 vaccines in either the standard or mixed schedules,” adds Matthew Snape, a vaccinologist at the University of Oxford, UK.

The studies sprang out of a natural experiment that began in March, when a number of countries partially or completely halted the use of the vaccine developed by the University of Oxford and the pharmaceutical company AstraZeneca in Cambridge, UK, because of extremely rare but serious side effects. This meant that some people who’d already received one dose of this vaccine then had a different vaccine as their second jab. Sester’s team and several others demonstrated that these mix-and-match combinations were safe and led to a strong immune response1,2,3.

Now, three teams have provided the first measurements of the effectiveness of mix-and-match regimens. The studies looked at various populations at various times — including during the rise of the hyper-infectious Delta variant — but they all agree that mix-and-match, or heterologous, vaccination is highly protective.

Beneficial mismatch

Epidemiologist Peter Nordström at Umeå University in Sweden and his co-authors analysed data in the country’s national health registers, which contain vaccination and COVID-19 testing and treatment information for all residents. They found that compared with unvaccinated people, those on a mixed vaccination schedule were 68% less likely to develop a symptomatic infection, whereas the 430,000 people who received two doses of AstraZeneca were 50% less likely to do so4. These and other figures make it clear that the heterologous regimens are more effective than two doses of AstraZeneca, Nordström says.

The conclusion echoes that of a similar analysis5 in Denmark, which has national health and vaccination registries similar to Sweden’s. Denmark halted all use of the AstraZeneca vaccine in April. Epidemiologist Mie Agermose Gram, at the State Serum Institute in Copenhagen, and co-authors found that one dose of AstraZeneca followed by one dose of Pfizer–BioNTech was 88% effective at preventing SARS-CoV-2 infection — an effectiveness similar to that of two doses of Pfizer. Their study has not yet been peer reviewed.

Knowing that mix-and-match vaccines are highly effective will have global implications, says Sester. There is some evidence that immunosuppressed individuals mount a strong immune response to mixed regimens7, so it’s possible that mixing doses could protect organ-transplant recipients and others with weakened immune systems better than do the standard regimens. The data could also support mixed immunization programmes in lower-income countries, where there might be shortages of certain vaccines. “These data are really important towards policies,” she says.



WHO in July 2021


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