Regulators in the US plan to let Americans “mix and match” booster shots of the Covid-19 vaccine.
This means that people will not be required to get the booster from the same brand used in their original inoculation, the New York Times first reported on Monday.
Early results from research being done by a US National Institutes of Health-led team shows that giving people a different type of booster shot from their original vaccine provided a stronger immune response than using an extra dose of the same vaccine.
The findings were in line with research conducted earlier in the year in Britain.
The NIH mix-and-match research started in June, and preliminary results released online Wednesday last week showed people who got the Johnson & Johnson vaccine as a first shot had a stronger immune response when boosted with vaccines from Pfizer and Moderna.
The results from 450 participants hint that J&J recipients who got a Moderna booster saw antibody levels rise 76-fold in 15 days, compared with four times after an extra J&J shot. A Pfizer booster gave the group a 35-fold increase in antibodies.
A growing number of countries are looking at switching to different Covid-19 vaccines for second doses or booster shots after supply delays and safety concerns slowed their vaccination campaigns.
The World Health Organization (WHO) said on July 12 that the practice was a dangerous trend because there was little data about the health impact. Europe's drug regulator on July 14 made no definitive recommendations on switching vaccines.
Researchers at the University of Oxford in the UK conducted some of the earliest research on mixing Covid-19 vaccines in studies conceived in late 2020. Known as the Com-COV study, for comparing Covid-19 vaccine schedule combinations, the team initially looked at mixing and matching the vaccines made by AstraZeneca-Oxford and Pfizer-BioNTech.
Interest, however, quickly shifted to whether such mixing, known in medicine as a heterologous vaccination schedule, could offer immunological advantages.
When the researchers gave 830 people either a double dose of the AstraZeneca or the Pfizer-BioNTech vaccines four weeks apart or a mix of each, all showed an immune response above the threshold, indicating good protection.
The strongest response occurred in people who first got the AstraZeneca shot followed by Pfizer.
With more than seven countries, including Canada, the EU and Qatar, having changed their guidelines and approved mixing and matching different brands of vaccines, should Kenya follow suit? The question has intrigued medical professionals, with some supporting the idea.
Catherine Kyobutungi, executive director at the African Population Health Research Centre, noted that adopting this strategy would be great because, on top of a stronger immune response, it makes it easier to continue vaccination programmes when one type of vaccine is in short supply.
“Countries have had to delay the second dose of AstraZeneca, for instance. They may not have to do that anymore if the policy is changed to allow mixing and matching,” said Dr Kyobutungi, an epidemiologist.
Dr Ahmed Kalebi, a consultant pathologist, supports the idea and explains that vaccines induce immunity by mimicking particular parts of the virus that are specific to each vaccine, thus multiple vaccine types will induce protection against different parts of the virus meaning better immunity.
But Dr Ombeva Malande, a vaccinologist and consultant on paediatric infectious diseases, noted that the current position is “no mixing and no third shots until WHO says so”.
The following countries are considering or have decided to adopt a mix and match approach:
UNITED STATES → US regulators expected to authorise boosters of the Moderna and Johnson & Johnson vaccines by Wednesday, October 20.
BRITAIN → As of September 27, a British study was looking into the immune responses of children to mixed schedules of different vaccines. Officials said that while the recipients will be given a first dose of the Pfizer-BioNTech shot, advice about second doses will be provided at a later date, while more data is gathered.
CAMBODIA → On August 1, Cambodia announced that a booster shot of the AstraZeneca vaccine would be offered to people who had received two doses of shots from either Sinopharm or Sinovac, while a Sinovac booster should be given to Cambodians fully inoculated with the AstraZeneca shot.
DENMARK → Denmark's State Serum Institute, which deals with infectious diseases, said on August 2 that combining the AstraZeneca vaccine with a second shot from either Pfizer-BioNTech or Moderna provides "good protection".
GERMANY→ In September, Germany started offering booster shots of the Pfizer-BioNTech and Moderna vaccines to vulnerable individuals such as pensioners and people with weak immune systems, regardless of which vaccine they had previously received.
RUSSIA→ On September 27 Russia's Direct Investment Fund said that a small-scale clinical study combining the AstraZeneca and Sputnik Light shots had shown strong antibody growth in a majority of the study's participants.
TURKEY→ Turkey is allowing people who have been inoculated with Sinovac's vaccine to receive an additional Pfizer dose as it looks to ease travel to countries that have not approved the Chinese shot, Turkey's health ministry said on August 16.