PSA: Booster (4th doses) for those immunocompromised.

In Canada, those who are moderately to severely immunocompromised and qualify for a three-dose primary series are eligible to receive a booster (4th dose), regardless of which vaccines they received for their 1st, 2nd or 3rd dose.

In Ontario, they are eligible to get a booster 4th dose as long as they are 84 days past 3rd dose. Interval for other provinces vary between 5-6 months.

In the US, the CDC guidance is similar: “Moderately or severely immunocompromised people who received an mRNA vaccine primary series and an additional primary mRNA vaccine dose should receive a single booster dose (preferably with an mRNA COVID-19 vaccine) at least 5 months after completing their additional primary dose. Those who received a single dose Janssen vaccine primary series should receive a single COVID-19 vaccine booster dose two or more months after the first dose, preferably with an mRNA vaccine instead of the Janssen vaccine.”