- The spread of the Delta variant has led some experts to believe a mRNA booster (by Pfizer or Moderna) may be needed for the J&J vaccine.
- However, recommending a booster top-up is premature at this stage, says Professor Linda-Gail Bekker.
- Data from the US, soon to be published, reveal that the vaccine is protective against this highly transmissible variant.
The spread of the highly infectious Delta coronavirus variant has thrown many countries a vaccination curveball. It has also been identified in more than 85 countries and has started to dominate third wave Covid-19 infections in South Africa.
While data suggest that Pfizer and Moderna's two-dose mRNA vaccines are effective at fighting this variant, the science has been less clear on the one-shot vaccine by Johnson & Johnson. This has led some health experts to believe that following up the single jab with a second dose of mRNA vaccine (by Pfizer or Moderna) may be necessary in the context of this troublesome variant.
But Professor Linda-Gail Bekker, co-lead investigator of the J&J Sisonke study in SA, said that recommending booster top-ups with another vaccine is premature. A press release by the South African Medical Research Council (SAMRC) on 1 July mentioned that the US will soon publish laboratory and antibody data showing that the immune responses – induced by the vaccine – mature over time and protect against the Delta variant.
“It doesn’t really suggest that a booster is not necessary, ever,” Bekker told Health24. “It just reassures that you don’t have to rush to have a booster dose right away, vis-à-vis the Delta variant.”
In fact, the data show that in the test tube, the J&J jab is more effective against Delta than against the Beta variant that was responsible for second wave infections in SA, and that the level of antibodies continues for a few months post-vaccination, said Bekker.
“So the durability is reassuring. And from that, we may confer that protection continues for some time. Therefore, we think that a booster dose at this stage in our healthcare worker Sisonke trial is premature. And we should continue to wait for more data to figure out whether – and when – a booster should be given,” she added.
Lab vs real-world data
There is the possibility of the vaccine showing effectiveness in the laboratory but not in the real world when it is rolled out, but Bekker explained that this information will be backed up with real-world effectiveness data. “We should be able to release some data on Sisonke,” she said.
The J&J ENSEMBLE phase 3 study is locking their database and will be releasing updated data in August 2021, she said, which will provide experts with the longevity of protection by the vaccine.
“So there’s more data coming down the pipe, but while we’re waiting for clinical data, the laboratory is a good, quick method to have a look and see if we can gain some insight [into protection against variants],” she said.
Sisonke study complete
The Phase 3b Sisonke study aimed to vaccinate 500 000 frontline healthcare workers against Covid-19 in South Africa. The trial is now complete and the researchers are in the process of completing a sub-study involving 1 400 participants, said Bekker.
A total of 479 768 healthcare workers received the jab, according to News24, although Bekker said a final count is still being done. She added that all participants will be followed up for two years until May 2023.
The SAMRC release indicated that of healthcare workers who had "breakthrough" Covid-19 infections, 94% were mild, 4% moderate and only 2% severe.
Breakthrough infections occur when a person tests positive for the Covid-19 virus despite being vaccinated against it. However, this isn’t unexpected as no vaccine is 100% effective at preventing illness in vaccinated individuals, explains the US Center for Disease Control and Prevention (CDC).
Defining moderate and severe cases
Having a moderate to severe breakthrough Covid infection would mean that a person would need hospital attention and be treated with oxygen or more intensive intervention, said Bekker.
“It’s the requirement of oxygen or some other sort of intensive, or high-care type intervention, whether it be dialysis, invasive oxygenation, high flow oxygenation, etc. It may not necessarily mean they need to be put in an ICU,” said Bekker, adding: “Mild symptoms would be something like sniffles, a snotty nose; maybe taking half a day off work.”
Are breakthrough infections shorter?
A recent CDC study, published in the New England Journal of Medicine, suggested that the mRNA vaccines result in breakthrough infections being shorter and infected people less contagious. Data on this for the J&J vaccine are not yet available, but the ENSEMBLE study is in the process of collecting data, said Bekker.
“If viral load [the quantity of virus measured in a person's nasal swab during testing] is reduced, one would hope that the individual would be less infectious. I think a reasonable conclusion to draw is that if the viral load is lower, which is what we believe the vaccines do across the board, then those individuals would be less infectious and would also return to health sooner.
“And that's sort of the basic principle when it comes to viral infections: the bigger the viral dose, the more infectious you are, and the longer it takes to get better,” she explained.
Following Covid protocols after vaccination
Bekker advises people who have been vaccinated in South Africa to continue adhering to non-pharmaceutical interventions (NPIs) to control the pandemic, including wearing a face mask and maintaining a physical distance.
She explained: “What we’ve seen from other countries, such as the US, is that as vaccination coverage gets higher, they begin to release some of those NPI requirements because many people are vaccinated.
“Generally, when the viral load across the board is lower and there’s far less infectiousness, you can start to relax things. But because vaccination coverage is still low in South Africa, people should take precautions – especially with the very transmissible Delta variant circulating.”
“What stands between us and getting any kind of pandemic control is the good coverage of vaccines,” said Bekker.
“And that means every citizen who is able to, should become vaccinated so that we can build that coverage and get to a place where this virus is subdued and is brought under control. And vaccines are the way to do so.”
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