Johnson & Johnson’s Covid-19 vaccine cuts the risk of getting infected with the disease by about half, a study of around half a million health workers showed. Most breakthrough infections were mild.The study included several weeks during which South Africa was going through a third wave of coronavirus infections, spurred by the highly contagious delta variant.Johnson & Johnson’s Covid-19 vaccine cuts the risk of
getting infected with the disease by about half, according to the latest
results of a trial involving almost half a million health workers in South
The vast majority of the breakthrough infections were mild,
Glenda Gray, co-leader of the study known as Sisonke, said in an interview,
citing unpublished data from the trial, which had earlier shown the shot’s
effectiveness against severe illness.
Like all Covid vaccines, J&J’s was intended and tested
for its ability to prevent Covid-19 hospitalisations and deaths. Even so, the
frequency of breakthrough infections in vaccinated people highlights the
challenge governments face in halting the virus’s spread, which threatens to
lead to the proliferation of new variants that may be even more contagious.
Coupled with vaccine hesitancy, the limited efficacy of
shots in stopping mild infections will mean “we will continue to see a
flow of infections,” said Bruce
Mellado, a professor at the University of the Witwatersrand in Johannesburg
who uses modeling to predict the trajectory of infections. Still, he said, the
effectiveness against death and severe disease could prevent a “human
J&J didn’t immediately respond to a request for comment.
The study included several weeks during which South Africa
was going through a third wave of coronavirus infections, spurred by the
highly contagious delta variant. The emergence of new, fast-spreading strains
has made earlier goals of herd immunity — when the proportion of the
population that’s vulnerable to the virus sinks so low that it stifles spread
— harder to reach.
By cutting the number and the intensity of infections,
the vaccines limit the chance of further mutated strains emerging.
Yet for many countries, the focus has shifted to reducing the seriousness of
illness and subsequent demand for more intensive treatments.
The Sisonke trial measured breakthrough infections both by
asking participants to report a positive result as well as by getting daily
alerts from testing laboratories. The researchers also tapped data systems to
see who had been hospitalised or died.
Initial results from Sisonke, released 6 August, showed
J&J’s single-dose vaccine was about 70% effective against hospitalisation
and as much as 96% effective against death. The trial didn’t include the use of
a placebo. The final results which include three sets of data from private
insurers and the government, will be submitted for publication in days, said
Gray, who’s a research professor at the University of the Witwatersrand.
The J&J vaccine, a key element in South Africa’s vaccination plan, has also been given to
teachers, police, and other government employees. It’s expected to play an
important role in reaching remote areas, as it can be stored at refrigerator
The Sisonke trial was put in place in February after the
South African government’s plans to use AstraZeneca Plc’s shot showed limited
efficacy against mild cases, disrupting government plans for a wide government
rollout. Gray and other scientists concluded an agreement with J&J to run a
Other vaccines in wide use have indicated vulnerability to
breakthrough infections. A study released 9 August showed that Moderna’s was
associated with a two-fold reduction of breakthrough risk compared with the
shot from Pfizer and BioNTech SE. The results were reported ahead of peer
The results against breakthrough infections are “not
unique to Johnson & Johnson, but also for other vaccines,” said Shabir
Madhi, a vaccinologist from the University of the Witwatersrand who led trials
of both AstraZeneca’s and Novavax’s shots in South Africa. “It comes as
little surprise with ongoing evolution of the virus.”