Does the COVID-19 vaccine still work if there is a longer time between doses? How do we know that the vaccine 4 months between dose 1 and 2 is okay?

The National Advisory Committee on Immunization (NACI)  state the following: “experience with other multi-dose vaccinations after a single dose suggest persistent protection could last 6 months or longer in adolescents and adults.”

What we know about vaccines in general is that we want to complete the vaccine schedule and get the recommended number of doses. Generally, vaccine manufacturing companies and national vaccine advisory bodies specify a minimum interval between vaccine doses but do not specify maximum intervals.

This is because for most vaccines, antibody levels (immunity) will go down over time and do not suddenly fall below protective levels. Even months or years later, another vaccine dose can boost antibodies (immunity) to higher levels.

In fact, for many vaccines, a longer interval to the booster dose results in higher antibody levels. High antibody levels are associated with longer duration of protection. So this is how we know that the 4 month interval between dose 1 and 2 of the COVID-19 vaccines is okay.

For more information:

• In B.C., while vaccine supplies are limited, the time between first and second dose will be extended so more people can receive their first dose, increasing the benefit of limited vaccine supplies. The National Advisory Committee on Immunization supports this strategy.
• Learn more about the evidence and the decision to defer the second dose of COVID-19 vaccine in B.C.