WHO warns of dangerous variants as infections rise
Australia joins nations facing global resurgence of Covid-19
The World Health Organisation (WHO) warned yesterday that “more dangerous” variants of Covid-19 could tear across the world as global infections soared to half a million daily, largely driven by the virulent Delta strain.
A tally of official sources found that after an initial dip, cases have been rising again worldwide since the end of June, topping 540,000 on Tuesday and again on Wednesday. “The pandemic is nowhere near finished,” the WHO’s emergency committee said. It highlighted “the strong likelihood for the emergence and global spread of new and possibly more dangerous variants of concern that may be even more challenging to control”.
The virus has reappeared in places long believed to have dodged the worst of the pandemic, with Australia facing a resurgence that has grown to almost 1,000 cases nationwide in a month. About 12 million Australians went under stayat-home orders in Melbourne.
Can we mix vaccines? The question is significant now since Covid-19 vaccination campaigns worldwide are underway, and the production and distribution of jabs have not kept pace. Two different vaccines for the first and second doses have been seen as the solution to swiftly inoculate populations to achieve the desired herd immunity that slows down the infection rate.
The two-vaccine strategy is fraught with risks as it is a relatively new frontier, despite attempts to fight HIV (the virus that causes AIDS) and Ebola with multiple vaccines. There have been some studies on the efficacy of using two drastically different vaccines against Covid, but the data is not adequate to advocate it as a strategy. That hasn’t stopped many countries from pursuing it.
Since two vaccines boost the immune system in different ways, multiple vaccines are expected to provide broader coverage.
Is it dangerous to combine two vaccines?
The World Health Organisation has warned against using different Covid-19 vaccines for the first and second doses. That chimes in with the UAE advice against using two vaccines.
In contrast, several countries in Europe and elsewhere have approved the combining of vaccines from two different platforms. But experts say more studies are required to ensure the safety of the two-vaccine strategy. “It’s a little bit of a dangerous trend here,” Soumya Swaminathan, WHO chief scientist, told an online briefing on Monday. “It will be a chaotic situation in countries if citizens start deciding when and who will be taking a second, a third and a fourth dose.”
Why mix vaccines?
A multiple-vaccine strategy involving doses from different platforms is called heterologous prime-boost vaccination. Since two vaccines boost the immune system in different ways, multiple vaccines are expected to provide broader coverage. Heterologous prime-boost was started in the 1990s by HIV researchers since a classical vaccine would not induce the extremely complex immunological mechanisms needed for potential protection from HIV infection, according to Dr Pierre Meulien, executive director of the Innovative Medicines Initiative (IMI). The first clinical heterologous vaccine was an Ebola vaccine approved in May 2020, while the Sputnik V Covid vaccine is also heterologous, reports say.
What do the studies on vaccine combinations say?
There’s been only a handful of studies on the efficacy of mixing different Covid vaccines, and that’s the worry. Right now, this is a “data-free area”, according to Soumya Swaminathan. “Data from mix and match studies of different vaccines are awaited — immunogenicity and safety both need to be evaluated, she added.”
At least four studies looked at the feasibility of mixing AstraZeneca and Pfizer-BioNTech vaccines in separate doses. The Spanish research Combivac found that the combination was highly effective in producing a robust immune response from the body; the results are published in the journal Nature. Trials by researchers in Saarland University and Ulm, Germany, also supported these findings, although they have not been fully evaluated.
The results from the University of Oxford’s Com-COV study showed that the side-effects were mild and moderate reactions. According to the study published in the journal Lancet, participants reported increases in chills, fatigue, headache, joint pain, malaise, and muscle ache.
Fatigue and headache were more frequent when the vaccines were mixed compared to two rounds of the same jab.
Matthew Snape, associate professor in Paediatrics and Vaccinology at the University of Oxford and chief investigator on the study, said the results are promising but cautions “they don’t resolve whether any improvement in T cell response results from longer dose intervals rather than the mixing”.
“So far, according to the amount of data we have, the best option is still not to mix vaccines,” Bloomberg quoted Ramon Lorenzo Redondo, a molecular virologist at Northwestern University, Illinois, US, as saying.
What happens when you mix vaccines?
“Mixing two types of vaccines may give the immune system multiple ways to recognise a pathogen. The mRNA vaccines are excellent at inducing antibody responses, and the vector-based vaccines are better at triggering T-cell responses giving a strong immune response,” Dr Ramesh Bhaskaran, Internal Medicine (specialist), Aster Hospital, Ghusais, Dubai. But mixing vaccines may carry the additional risk of serious adverse effects too, the Dubai-based doctor cautioned.
Is it safe to mix vaccines?
“There is no exact data about the safety of mixing Covid vaccines. However, a small study published in the medical journal Lancet recently showed a slight increase in intensity and duration of the minor side effects like pain, fever and fatigue. No major adverse event was reported on mixing vaccines,” said Dr Idrees Mubarik, Endocrinology (Specialist), Aster Hospital, Mankhool and Ghusais, Dubai.
Covid-19 vaccines and their platforms
“Covid-19 vaccines are being developed using several different platforms. The major antigenic target is the large surface spike protein. Immune responses to a SARS-CoV-2 inactivated vaccine (Sinopharm) would target not only the spike protein but also other components of the virus.
“Pfizer and Moderna vaccines employ messenger RNA, which induces our cells to produce viral proteins that stimulate a potent immune response. They contain material from the virus that causes Covid-19 that gives our cells instructions for making a harmless protein that is unique to the virus. After our cells make copies of the protein, they destroy the genetic material from the vaccine. Our bodies recognise these proteins and build T-lymphocytes and Blymphocytes that will remember how to fight the virus if we are infected in the future.
The AstraZeneca vaccine uses a chimpanzee adenovirus to stimulate the immune system to produce antibodies. Basically, the vehicle for delivery of the spike protein is different, and it induces immunity by targeting different aspects of our immune system,” Dr Bhaskaran said.
Have multiple vaccines been administered previously?
“In polio, different types of vaccines have been used, both oral and injectable vaccines have been used in some children with reassuring safety,” said Dr Mubarik.
Dr Bhaskaran said: “Immunologists have tested mixing doses of different vaccines for long. HIV researchers have long been exploring this for HIV vaccination. The Ebola vaccine is an example of an effective mixedproduct vaccine. The first shot uses the same adenovirus vector as AstraZeneca’s vaccine, and the second uses a modified version of a Poxvirus called Modified Vaccinia Virus Ankara (MVA). These are two different types of pneumococcal vaccines that have different mechanisms of action, and in certain situations, we recommend boosting one with the other.”
What doctors think of mixing Covid-19 vaccines
“My personal opinion regarding the mixing of vaccines is that it should not be routinely done until further safety data emerges. Also, it would have been much better if travel guidelines by different countries emphasise vaccination in general rather than any particular brand of vaccine,” said Dr Mubarik.
“The serious risks of rare side effects is one reason some researchers recommend that people stick to the standard two shots of a single vaccine for now. When combining two different vaccines, both of which might have their own profile of adverse events and effects, could amplify problems. When given an option of either getting a mixed schedule or no second dose, then you certainly go for the mixed schedule,” said Dr Bhaskaran.