Johnson & Johnson's COVID-19 vaccine works well against the delta variant and the immune response lasts at least eight months, the company said Thursday, citing lab tests of vaccine recipients' blood.
“Current data for the eight months studied so far show that the single-shot Johnson & Johnson COVID-19 vaccine generates a strong neutralizing antibody response that does not wane," Dr. Mathai Mammen, global head of Janssen Research & Development, Johnson & Johnson, said in a news release. "Rather, we observe an improvement over time."
The report comes as some people who have received the one-dose vaccine have wondered whether they'd need a booster against the highly contagious, mutated virus. The delta variant, which was first identified in India, now accounts for 25 percent of new COVID-19 cases in the United States and has been detected in all 50 states.
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Two doses of the Moderna and the Pfizer-BioNTech mRNA vaccines have shown to be highly effective against all the known coronavirus variants, but it was previously unclear whether the Johnson & Johnson vaccine also protected against the delta mutation.
Some scientists and doctors tweeted concern on social media over a June 14 analysis from Public Health England that found a single vaccine dose of AstraZeneca was less effective against symptomatic illness caused by the delta variant, suggesting that people who had received the one-dose Johnson & Johnson vaccine would need a booster shot from one of the mRNA vaccines.
Separate research from the United Kingdom found that mixing a dose of AstraZeneca and an mRNA vaccine produced a stronger immune response than two doses of AstraZeneca. The Johnson & Johnson and the AstraZeneca vaccines are different, but share a similar technology, called a viral vector.
During a White House briefing Thursday, Dr. Anthony Fauci said that guidance on vaccine boosters in the U.S. would be based on clinical data.
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"We need to remember, the Johnson & Johnson vaccine is a highly effective vaccine," Fauci, director of the National Institute of Allergy and Infectious Diseases, said during the briefing.
More than 12 million doses of the Johnson & Johnson vaccine have been administered in the U.S. according to the Centers for Disease Control and Prevention.
This story first appeared on NBCNews.com.