Johnson & Johnson says its one-shot COVID-19 vaccine holds up against the Delta variant

More than 12 million Americans have rolled up their sleeves for the Johnson & Johnson COVID-19 vaccine.

Now, preliminary but promising data shows the single-shot vaccine appeared to work well against multiple concerning variants, including the Delta one. It's more data that supports its effectiveness.

"If you got your dose, you're good. It provides a lot of protection and it looks like it's holding its own as well against our variants," said L.A. County Public Health Director Barbara Ferrer.

While the results have not been peer-reviewed, Johnson & Johnson scientists say earlier clinical trials had shown the vaccine offered 66% protection against symptomatic infection and that the immunity held up for at least 8 months.

"I personally got the (Johnson & Johnson) vaccine and I personally feel very comfortable waiting and not going and running off and getting another vaccine right now," said Dr. Kenneth Kim, a vaccine researcher and principal investigator in the J&J vaccine trials.

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Moderna just released lab data indicating two doses of its vaccine produced enough neutralizing titers to protect against the Delta variant.

A study based on real-world data from the United Kingdom demonstrated two doses of the Pfizer vaccine are 88% effective. The efficacy of the mRNA vaccines have left many recipients of the Johnson & Johnson vaccine wondering if they should reinforce their immunity with an extra dose of either the Pfizer or Moderna shot.

Experts say, for now, there is no need.

"You can be reassured that all of the information we have right now indicates there's no reason for you to start with a different vaccine," said Ferrer.

Delta variant of COVID-19 a rising concern in Los Angeles County

While overall COVID-19 rates remain relatively low in Southern California amid continuing vaccination efforts, officials are increasingly worried about a growing threat from the delta variant.

"It makes sense in theory but we really need to see studies to make sure there is an increase in effectiveness that would be valuable," said Infectious Disease specialist Dr. David Bronstein with Kaiser Permanente.

"You're going to have more side effects.. Our body is going to feel the fact that you've been exposed before," said Kim.

All vaccines have risks of side effects so most experts agree it's better to err on the side of caution. There have been reports of a very small number of dangerous blood clots occurring in people who received the Johnson & Johnson vaccine. Most of the cases resolved themselves, but it led the U.S. government to briefly pause its rollout in April.

Following a safety review, the CDC and the FDA resumed its use.