The first single-dose COVID-19 vaccine continues to show promise, but it may be months before it is available.

Interim results from first and second phase trials of the Johnson &Johnson COVID vaccine have been published in the New England Journal of Medicine, and they are better than expected. More than 90% of those given the drug showed an immune response, and that response appears to be long-lasting.

The early stage trials do not specifically show how effective the vaccine is against COVID-19, but researchers say evidence of an immune response of promising. J&J hopes to report on its late-stage testing in a matter of weeks. The current Pfizer and Moderna vaccines have been shown to be as more than 90% effective in preventing COVID-19 infections. J&J researchers are hoping for the same.

The J&J vaccine has some significant advantages over others that have been approved for emergency use or still in development. It requires only one dose to be effective. Both the Pfizer, Moderna and AstraZeneca (not yet approved by the FDA) vaccines require two doses, given weeks apart. The Pfizer vaccine also requires deep cold storage, making transport and distribution challenging. Current vaccines also have a very short shelf life. Once opened, all the vaccine in a vial must be used in a matter of hours. The J&J vaccine can be stored at normal refrigerator temperatures for months at a time.

The benefits of having a long-lasting, easily transported and shelf stable vaccine may outweigh the J&J vaccine expected lower effectiveness. J&J Chief Scientific Officer Paul Stoffels said in an interview with Time there was good reason to believe the vaccine would have "high levels of efficacy.” As high as 90%? Stoffels said, “I don't know. The data will tell us.”

Government scientists are not expecting the J&J vaccine to be as effective as the two currently in use. Moncef Slaoui, the chief scientific adviser to the U.S.’s Operation Warp Speed vaccine development and distribution effort, told Time he expects effectiveness in the 80-85% range. That is still extraordinary effectiveness for a vaccine. As they were first being developed, the FDA signaled they would approve any vaccine with an effectiveness of 50% or better. By comparison, the annual Influenza vaccine has averaged less than 40% effectiveness over the last 15 years.

As New Jersey expands the number of people who can start receiving the currently approved vaccine, it's unlikely the J&J shot will be added to the state arsenal anytime soon. Aside from regulatory hurdles there have been reports J&J is falling behind in production. 12 million doses were promised by the end of February, but POLITICO reported this week that J&J may not meet that goal until the end of April. A J&J spokesman did not confirm or deny that report, but told POLITICO they "remain confident in our ability to meet our 2021 supply commitments."

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