KUALA LUMPUR: Heterologous boosting, particularly with a mRNA vaccine, offers higher protection against Covid-19 variants of concern, like Delta and Omicron, and prevents hospitalisation and death.
Experts said heterologous boosters, or the "mix-and-match" approach (administration of booster shots that are different from the initial vaccine), with an mRNA jab, either Pfizer-BioNTech or Moderna, is highly effective and significantly strengthens the immunity.
Universiti Malaya epidemiologist Professor Datuk Dr Awang Bulgiba Awang Mahmud said several studies on heterologous prime-boost (using a different vaccine as the second dose) and heterologous booster approaches suggest this.
He said the European Medicines Agency had stated that evidence indicated that in terms of immune responses, a heterologous booster approach appeared to be as good as or better than a homologous booster approach (where the same vaccine type is used as the booster).
"Among the heterologous booster combinations, boosting with an mRNA after a vector primary series is more immunogenic than the reverse," he told the New Sunday Times.
"In addition, the safety profile of heterologous and homologous booster combinations remains comparable based on the data available."
Dr Awang Bulgiba, who is also Science, Technology and Innovation Ministry's Covid-19 Epidemiological Analysis and Strategies Task Force chairman, said a New England Journal of Medicine study found that the rates of confirmed Covid-19 and severe illnesses were substantially lower among those who received a Pfizer booster shot.
"(An article published in The Lancet on Sept 4 showed) the heterologous prime-boost approach to be better at inducing antibodies compared with the homologous prime-boost approach.
"In all these studies, there were few adverse events which might cause concern, but the heterologous prime-boost or heterologous booster approach has been shown to be safe."
He was commenting on renewed concerns on social media over the mixing and matching of vaccine types (AstraZeneca's viral vector and Pfizer's mRNA) as booster shots were being administered nationwide following the emergence of the Omicron Covid-19 variant.
Some Malaysians who received AstraZeneca as their primary dose were on the lookout for the same vaccine as a booster amid safety and efficacy concerns.
Dr Awang Bulgiba said concerns arose due to several reasons, which include the information being disseminated on the homologous and heterologous approaches, leading to confusion among the public.
Besides that, he said, new knowledge on vaccination approaches was appearing at dizzying speeds, making it difficult for the layperson to digest.
There was also rampant disinformation on Covid-19 vaccines, and this newer heterologous approach was easily exploited by anti-vaxxers bent on discouraging people from being vaccinated, he said.
"One of the biggest problems with the country's pandemic management has been the poor crisis communication in all aspects, whether it is to do with non-pharmaceutical interventions or vaccination.
"Our vaccination drive has been successful in part because the surge of cases during the third wave quelled population fears about vaccinations and drove up vaccination uptake."
He said following the recent decline in case numbers and deaths, complacency had set in, which was being exploited by anti-vaxxers to plant doubt on the need for boosters and to stoke fears about the heterologous booster approach.
"Yet, in truth, from childhood, we have received many types of vaccines, ranging from toxoids to live attenuated and inactivated virus vaccines, with few adverse events reported from mixing these vaccines.
"In fact, there has been a shift in polio vaccination, where a mixed approach is now being used by some countries, where early doses of the oral live attenuated poliovirus vaccine may be followed by a later dose of an injected inactivated poliovirus vaccine."
He added that the best way to allay fears was to run a booster vaccination campaign with the help of credible scientific experts advised by behavioural scientists and communication specialists.
Universiti Sains Malaysia (USM) virologist Dr Kumitaa Theva Das said studies on heterologous vaccination had demonstrated that the mix-and-match approach was not only safe, but also provided better protection.
A Swedish study, she said, showed that those on a mixed vaccination schedule were less likely to develop a symptomatic infection compared with those who received doses of the same vaccine.
The study, published in The Lancet Regional Health (Europe) on Dec 1, 2021, involved more than 10,000 people who received their first dose from AstraZeneca and their second from Pfizer or Moderna. It also found that the heterologous viral vector-mRNA vaccine works well with few adverse events.
The study, which was also reported by the European Pharmaceutical Review, suggests that an mRNA booster had a 68 per cent effectiveness, greater than the 50 per cent effectiveness for homologous AstraZeneca shots.
"In Malaysia, some of the early mix-and-match data shared with the public were from Chile and Thailand.
"Countries like UAE, Brazil, Indonesia and Turkey have offered similar boosters to Chile and Thailand, where inactivated vaccines (such as Sinovac) were initially used, and mRNA or viral vector vaccines were subsequently offered as boosters.
"A clinical trial funded by the National Institute of Allergy and Infectious Diseases of the United States, which evaluated Covid-19 vaccine mixing in hundreds of patients, found that all boosters increased neutralising antibody titers, irrespective of the kind of booster or primary vaccines used.
"No safety concerns have emerged so far. In all cases, the mix-and-match approach was safe and highly protective."
Dr Kumitaa, who is USM's Infectomics Cluster, Advanced Medical and Dental Institute senior lecturer said in terms of the heterologous booster shots in Malaysia, the mRNA vaccines were the primary recommended boosters.
Similarly, she said, in the United States, the United Kingdom and Australia, all mRNA vaccines (Pfizer and Moderna) were the primary recommended boosters.
"The reason for this is based on some early data from South Africa, which suggests that the mRNA vaccines provide slightly better antibodies (and longer) protection against Omicron compared with the other vaccines.
"However, if you received AstraZeneca, Sinovac, Sinopharm, Sputnik or Jansen, AstraZeneca is also a suggested alternative.
"Any booster shot is better than none as all vaccines provide antibody protection and other defences (such as B and T cells) that are built up after booster shots.
"All these defences go a long way in protecting us, and have been studied thoroughly by many countries, reviewed thoroughly by regulatory bodies and overseen by the World Health Organisation to validate and confirm safety."
She said the constant updates on vaccines and the administration approach could seem scary, but that only meant that the public was constantly getting new information on this evolving virus.
Public health expert and epidemiologist Datuk Dr Zainal Ariffin Omar said evidence from clinical and epidemiological studies, and observations around the world, showed that mixing and matching of Covid-19 vaccines was safe, effective and even better for some of the regimes.
"The fear is mostly individual perception and based on incomplete information. But the benefits of booster doses outweigh the minor risks of the approach.
"For Malaysia, we should follow the government recommendations and get the booster as soon as possible. However, since we have several options of vaccines, people can have their preference of vaccine provided by the government or privately."
He added that the government should continue to evaluate the effectiveness of the mix-and-match approach and share the findings and information with the public.