You are correct that the second Shingrix dose is to be administered 2 to 6 months after getting the first dose according to the Centers for Disease Control.
This administration schedule, like most vaccines, was determined mostly from data obtained from clinical trials for the vaccine.
In fact, according to the study published in the journal Vaccine, three different dosing schedules were tested for Shingrix:
- Two doses, with the second dose being administered 2 months after the first (i.e. 0-2).
- Two doses, with the second dose being administered 6 months after the first (i.e. 0-6)
- Two doses, with the second dose being administered 12 months after the first (i.e. 0-12)
The results of the study concluded that the '0-2' dosing schedule and the '0-6' dosing schedule were 'non-inferior', a statistical term meaning that both schedules are considered to be as effective as one another (within a given deviation).
The '0-12' dosing schedule did not demonstrate 'non-inferiority' to the other two which is why Shingrix is only recommended to be dosed 2-6 months after the first dose.
Unfortunately, there have been no studies completed testing whether or not Shingrix loses effectiveness, or if there is an increased risk of side effects if the second dose is given too soon.
Nevertheless, there certainly is a concern that not following the recommended wait time between doses could cause it to be less effective when it comes to preventing shingles.
The Centers for Disease Control has a fairly extensive practice guideline covering vaccine schedules and minimum dosing intervals. They state that getting doses too close together could result in a reduced immune response:
"In clinical practice, vaccine doses occasionally are administered at intervals less than the minimum interval or at ages younger than the minimum age. Doses administered too close together or at too young an age can lead to a suboptimal immune response."
Although there are no studies that evaluated whether or not getting the second dose of Shingrix too soon reduces immune response, the Advisory Committee on Immunization Practices recommends the following:
"The recommended interval between RZV [Shingrix] doses is 2 to 6 months. The minimum interval between doses of RZV [Shingrix] is 4 weeks. If the second dose is given less than 4 weeks after the first dose the second dose should be repeated at least 8 weeks after the invalid dose."
So, there is a definitive recommendation to repeat the second dose of Shingrix if it was accidentally given less than one month (4 weeks) from your first dose.
In your situation, even though you received your second dose before the recommended interval (6 weeks) you are still within the acceptable minimum interval (4 weeks). You do not have to have your dose repeated. Nevertheless, it is unknown whether or not the vaccine is as effective in this case versus following the recommended schedule.
In regard to an increased risk of side effects, it isn't known if getting the second dose prior to the recommended interval increases their incidence.
Most side effects experienced after receiving the vaccine are minor and transient. We wrote an article detailing them, which can be found here:
The fever and chills you are experiencing are fairly commonly reported side effects. In fact, 'shivering' was reported in over 35% of individuals aged 50-59 and fever was reported in over 27% of individuals in the same age group.
They should begin to resolve after a few days. If they are not getting better, or they become more severe, it is important to speak to your doctor to be properly evaluated.
Answer SummaryShingrix is given in two doses. The recommended dosing schedule is for the first dose to be given initially, followed by a second dose administered anytime between 2 and 6 months later. However, the Advisory Committee on Immunization Practices (ACIP) states that the minimum interval between doses Shingrix is 4 weeks. It is unknown whether or not receiving the second dose prior to 2 months (8 weeks) decreases effectiveness or increases side effects. If the second dose is given less than 4 weeks after the first dose, the second dose should be repeated.
- ^ Immunogenicity, reactogenicity and safety of 2 doses of an adjuvanted herpes zoster subunit vaccine administered 2, 6 or 12 months apart in older adults: Results of a phase III, randomized, open-label, multicenter study. ScienceDirect
- CDC Timing and Spacing of Immunobiologics.
- CDC Recommendations of the Advisory Committee on Immunization Practices for Use of Herpes Zoster Vaccines.