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MLHU Clarifying Second Dose Intervals and Medical Officer of Health Strongly Endorsing Vaccine Interchangeability

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In order to maximize protection against the emerging Delta variant of COVID-19, the Middlesex-London Health Unit is accelerating second doses for anyone who received a vaccine on or before May 9th. In addition, the Health Unit is clarifying the rebooking intervals for those who are eligible to schedule new second dose appointments. A press release issued June 15th incorrectly implied a minimum eight-week interval for all clients. The eight-week minimum is only for those who received AstraZeneca for their first dose. For those who received Pfizer or Moderna for their first dose and are eligible to re-book a second-dose appointment, the minimum rebooking interval is 28 days after receiving their first dose.

Criteria for rebooking second doses earlier include:

In addition, the Medical Officer of Health is strongly endorsing use of any available mRNA vaccine for second doses. Clinics will provide the same vaccine as the first dose, if it is available. If it isn’t available, another vaccine will be provided. Emerging data and consensus among experts is that Pfizer and Moderna are interchangeable. This principle of interchangeability is an important component of the Health Unit’s effort to deliver more vaccine to more people more quickly.

“Regardless of what you received for your first dose, Pfizer and Moderna are both excellent options for a second dose, and clients will receive the vaccine that is available,” says Dr. Chris Mackie. “AstraZeneca is also a great second dose option for those who received it for their first dose.”

How to book a new second-dose appointment:

  • Book online at (new appointments open daily at 8:00 a.m.)
    • For those vaccinated on or before May 9th who need to re-schedule a shorter-interval second dose appointment, enter Gate #4 I need to re-book my scheduled second dose.
    • For individuals who received their first dose in another setting or out of region and need to book a second dose within four weeks of their first dose, enter Gate #5, I received my first dose elsewhere and now need to book a second dose.
  • Phone lines are often busy, and online is the recommended route for rebooking. However, calling remains an option at 226-289-3560 (8:00 a.m. to 7:30 p.m., Monday to Sunday)

Media Contact:
Dan Flaherty, Communications Manager, Middlesex-London Health Unit, 519-663-5317 ext. 2469 or 519-617-0570 (cell.)

Dr. Chris Mackie, Medical Officer of Health, Middlesex-London Health Unit

Tags: COVID-19, Vaccine