Regulatory Decision Summary for Spikevax

To support authorization of the Spikevax booster dose, the immune response and safety data from a subset of subjects from the ongoing study P201 Part B were provided. These subjects were 18 years of age and older, had received two doses of Spikevax (100 mcg) as an initial series, and then approximately 6 months after the second dose, they received a Spikevax booster dose of 50 mcg.

Antibody levels in 149 participants on Day 29 after the booster dose were found to be 13 times higher than before receiving the booster dose. The antibody levels in those participants were also compared to the antibody levels in a random sample of participants from the phase 3 Study P301 (N=1055), assessed on Day 57 after an initial series with 100 mcg Spikevax. This comparison indicated a 1.8-fold increase in antibody levels following the booster dose relative to levels following the second dose of the initial series.

171 participants were followed-up for safety for at least 1 month after receiving the 50 mcg Spikevax booster. Safety and immune response data from 6-months and 12-months of follow-up will be provided to Health Canada when available.

The solicited adverse reaction profile for the booster dose was similar to what was identified after the second dose in the primary series. The most common solicited local adverse reactions (ARs) were pain at injection site (84%) and axillary swelling or tenderness (20%). The most common solicited systemic ARs were fatigue (59%), headache (55%), myalgia (49%), arthralgia (41%), and chills (35%). The most common unsolicited AEs were headache (2.3%) and fatigue (2.3%). All unsolicited AEs were mild or moderate in severity. Among the participants who received a booster dose of Spikevax, there were no serious adverse events reported from the booster dose through 29 days after the booster dose. No cases of severe allergic reaction (anaphylaxis), blood clotting events, nerve-related events (Bells palsy, Guillain-Barre Syndrome [GBS]), or heart-related events (myocarditis/pericarditis) were reported.

The exact timing of the booster doses and identification of the appropriate populations who should receive booster doses depend on a variety of factors including the local epidemiological contexts which are continually evolving and may vary between provinces and territories. As such, the decision of when and to whom to offer a booster dose should be made considering relevant vaccine effectiveness data (e.g. evidence of waning effectiveness), taking into account the available safety and immune response data.

Based on the totality of the information, the benefit-risk profile of a 50 mcg booster dose of Spikevax is considered favourable in individuals 18 years of age and older.