There is no clear data on the vaccine’s efficacy in the current monkeypox outbreak since the disease has only been spreading in non-endemic countries since May 2022, and the Jynneos vaccination campaign only recently began in the US. We’ll likely have some more answers on how well the shot’s working sometime next year.
How long is too long to wait for the second dose?
According to Dr. Gandhi, there’s strong evidence to suggest that spacing out vaccine doses can improve a person’s immune response in the long term. This has even been observed with the COVID vaccines, for example; preliminary evidence suggests that waiting up to 11 or 12 weeks between doses may provide stronger protection than giving the shots three weeks apart. “If you exceed the one-month interval [with the Jynneos vaccine], you’re still fine—in fact, you may be even better off,” Dr. Schaffner says, as long as you eventually complete the full monkeypox vaccination series.
So, is there an amount of time that could be too long to wait for the second dose? The short answer is no, according to Dr. Schaffner. This hasn’t been specifically studied in the Jynneos series, but past research strongly reinforces this line of thinking. “We’re really quite confident that even if you go two, five, six, eight months, a year later and you get that second dose, that your immune system—primed by the first dose—will have a really big second-dose response,” Dr. Schaffner says.
The FDA also recently decided that the Jynneos vaccine, which was originally approved for subcutaneous (beneath-the-skin) use, can be given intradermally (between layers of skin) and at lower doses. It based that decision, in part, on a 2015 study that found intradermal injections at 1/5th the dose led to a similar immune response compared to those who got the full dose injected into the arm muscle.
How to stay safe until you can get your second monkeypox vaccine
All that said, the full two-dose series is needed for optimal protection against monkeypox. “Until you get your second dose, you could assume that maybe you have partial protection, but probably not full protection,” Dr. Gandhi says. Peak protection kicks in about two weeks after you receive the second dose.
Monkeypox can spread in various ways, but intimate, prolonged skin-to-skin contact is driving the current outbreak, the CDC says. While you’re waiting for your second dose, the most effective way to lower your risk is to limit intimate or sexual activity, says Dr. Gandhi, or at least be especially cautious about it. Practicing good hand hygiene (which we’re sure you know how to do by now!) and avoiding close skin-to-skin contact with anyone who has a suspected monkeypox rash can also reduce your chances of infection.
In the meantime, rest assured that more doses are coming. The US Department of Health and Human Services recently ordered an additional 5.5 million doses of the Jynneos vaccine and public health experts expect them to become available later this year. Because an ample supply of Jynneos doses is on the horizon, public health experts do not expect the country to use the ACAM2000 vaccine. Dr. Schaffner says he’s not even aware of any providers that carry ACAM2000, since it’s associated with adverse effects and is more difficult to administer.
Unfortunately, just as experts learned during the height of the COVID pandemic, only time will tell us just how effective the one-dose strategy is. As the monkeypox public health emergency accelerates, health officials say the most prudent thing to do is to make sure vulnerable people have at least some protection against the virus while we wait.