Two (2) doses of Moderna Spikevax XBB.1.5 or 3 doses of Pfizer-BioNTech Comirnaty XBB.1.5 are recommended, with an 8-week interval between doses. An additional dose is recommended for individuals who are moderately to severely immunocompromised, with an interval of 4 to 8 weeks between each dose (see Table 1 for schedules and dosages).
The 8-week interval is longer than the authorized interval and is recommended as a better immune response has been associated with a longer interval between doses. For those who are moderately to severely immunocompromised, the 4 to 8-week interval between doses needs to balance a potentially better immune response with longer intervals with the need for earlier protection due to risk of exposure from circulating SARS-CoV-2 and the risk of severe COVID-19 disease.
Those who are moderately to severely immunocompromised are recommended to receive an additional dose in the primary series compared to those who are not immunocompromised in order to help improve the immune response and vaccine effectiveness in this group (based on data from adults). Those who are moderately to severely immunocompromised generally respond less well to COVID-19 vaccines and are at higher risk for severe illness.
If children 6 months to under 5 years of age started the primary series with a non-XBB.1.5 vaccine (i.e., original monovalent, BA.1 bivalent or BA.4/5 bivalent) but did not complete the series, they should complete the primary series with an XBB.1.5 vaccine (see Table 2).
For children 6 months to under 5 years of age who are moderately to severely immunocompromised, a 3-dose series of the Moderna Spikevax (25 mcg) vaccine is preferred over 4 doses of Pfizer-BioNTech Comirnaty (3 mcg) because there is likely higher acceptability and more feasible implementation due to fewer doses in the schedule using Moderna Spikevax.
A mixed product schedule using vaccines from different manufacturers can be offered for the primary series, however if both Pfizer-BioNTech Comirnaty and Moderna Spikevax vaccine products are used in the same primary series for an individual 6 months to under 5 years of age, the total number of doses in the series should follow the Pfizer-BioNTech Comirnaty schedule (see Table 2).
Children who started the primary series with a non-XBB.1.5 vaccine at less than 5 years of age and turn 5 years of age before completing the series, should receive the number of XBB.1.5 vaccine doses recommended as per Table 2 for those 5 years of age and older (including relevant footnotes). Children who started a primary series with an XBB.1.5 vaccine at less than 5 years of age and turn 5 years of age before completing the primary series, should receive the following with the age-appropriate dosage for their current age: