A single dose of Johnson & Johnson’s experimental COVID-19 vaccine produced a strong immune response against the new coronavirus in an early to mid-stage clinical trial, according to interim results released Friday.
The vaccine, called Ad26.COV2.S, was equally well tolerated at two different doses, the results showed. A single injection, versus a rival two-dose approach being tested by Moderna Inc and Pfizer Inc, could simplify the distribution of the vaccine.
However, it is not clear if older people, one of the populations most at risk of contracting the virus, will be protected to the same degree as younger people with the J&J vaccine.
The trial in about 1,000 healthy adults, which is supported by the US government, began after the J&J vaccine was discovered in July to offer strong protection in a single dose to monkeys.
Based on current results, J&J began a final test of 60,000 people on Wednesday, which could pave the way for a request for regulatory approval. The company said it expects the results of the so-called Phase 3 test by the end of the year or early next.
The results, published on the medRxiv medical website, have not been peer-reviewed.
The researchers, including those from J & J’s unit Janssen Pharmaceuticals, said that 98% of the participants with data available for interim analysis had neutralizing antibodies, which defend cells from pathogens, 29 days after vaccination.
However, the immune response results were available for only a small number of people (15 participants) over 65 years of age, limiting interpretation.
In participants older than 65, the rate of adverse reactions such as fatigue and muscle aches was 36%, much lower than the 64% seen in younger participants, the results showed, suggesting that the immune response in the older people may not be that strong.
The researchers said more details on safety and efficacy will be released when the study is completed.
For now, the results justify why more studies are needed in larger numbers to look for serious adverse effects, Dr. Barry Bloom, a professor at Harvard’s TH Chan School of Public Health who was not involved in the J&J trial, told Reuters.
“Overall, the vaccine is doing what you would expect it to do if you moved it to Phase 3 trials,” said Bloom.
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