Table of contents

Posted by

Dr. Deena Hinshaw


September 29, 2022



Annual fall influenza vaccines are a familiar routine for us, and right now this routine is lining up with COVID-19 vaccine boosters. Just like getting an annual influenza vaccine, keeping up to date with COVID-19 vaccine doses is important to reduce the chances of becoming seriously ill and needing to be hospitalized.

Bivalent vaccines

We now have the advantage of bivalent vaccines that include an Omicron strain along with the original strain. In Canada, the first bivalent vaccine that is available contains the BA.1 Omicron strain, and early research shows better antibody response against all major Omicron lineages when compared with the original vaccine. This is good news, as this means it is expected that this bivalent vaccine will offer additional protection for not just BA.1, but multiple sub-lineages.

There are also bivalent vaccines containing the BA.4/5 Omicron strain that could be available in mid to late October. Laboratory research on the BA.4/5 bivalent vaccines also shows stronger antibody responses against Omicron lineages than the original vaccine strain.

It is not yet clear whether there will be a difference in protection between the BA.4/5 bivalent compared with the BA.1 bivalent vaccine – both offer broader coverage than the original. For those who are eligible now and are at risk of exposure in the short term, taking the BA.1 vaccine will provide good additional protection sooner than waiting for the BA.4/5 bivalent vaccine.

Vaccine intervals

Boosters were made available in late July to support those who were at highest risk of exposure or severe outcomes from the summer COVID-19 wave, and for whom many months had passed since their last dose. Some who received COVID-19 vaccine in the summer may now be interested in a bivalent booster dose, and want to know how long they need to wait.

The timing of a booster dose is important not just for short term benefit but also longer term benefit. Those who received a summer booster will still have protective effects from that dose and it is recommended to wait at least 5 months before getting another dose of COVID-19 vaccine since we know that a longer time between vaccine doses is better for optimal response. This maximizes the benefit over time, particularly looking at the time of anticipated highest risk in the late fall and early winter.

A shorter minimum interval of 3 months can be considered, particularly for those at highest risk of severe outcomes in the short term such as those living in long term care who will have the opportunity to receive bivalent vaccines through outreach programs beginning in October.

Hybrid immunity

We now know more about the interaction between infection with SARS-CoV-2 (the virus that causes COVID-19) and immunization. While infection does produce an immune response, infection plus immunization provides better protection than infection alone. This combination of vaccine protection and infection results in 'hybrid immunity'.

For those who have had a primary series of vaccine and then had COVID-19, the infection can act like a booster. Because of this, the benefit from another dose of vaccine may be optimized by waiting the same length of time from infection to an additional dose as from one vaccine dose to another. At this time, it’s recommended to wait at least 5 months after infection before getting a booster dose for the same reasons outlined above. Similar to the vaccine interval, those at highest risk of severe outcomes could receive a fall booster at 3 or more months from an infection.

Exposure risk

Finally, an important consideration is the timing of exposure. Knowing that the greatest protection after a COVID-19 vaccine is experienced two weeks to several months after receiving it, it makes the most sense to offer it shortly before a time of high exposure risk.

This is why our annual influenza vaccine campaign happens in October – the highest transmission time for influenza is typically November through January. We do not know exactly what COVID-19 transmission will look like this fall and winter, but it is reasonable to assume the same factors that typically drive influenza risk will also increase COVID-19 risk, and a COVID-19 wave would be anticipated at this same time. For those who are eligible, getting a vaccine from now through October will help to increase protection in the subsequent months.

Current context

We are in a different context this year than last fall. As Omicron and its sub-variants have become our dominant strains, the vaccine’s main benefit over the longer term is to reduce the risk of severe outcomes. Boosters, and especially the bivalent boosters, can address waning protection over time and are also likely to improve protection against infection in the few months following the booster.

If it has been more than five months since a previous dose or infection, for those who have risk factors such as living in seniors’ congregate care settings, age over 50, or medical risk factors such as diabetes or kidney disease, getting a fall booster is one of the best ways to protect yourself against severe outcomes from COVID-19. With the influenza vaccine arriving in pharmacies in mid-October, one option would be to plan to receive both vaccines together at that time, or you can get the COVID-19 bivalent vaccine now and the influenza vaccine next month.

For those without risk factors who have had a primary series (for most people this is two doses) plus a booster in the past year, the risk of severe outcomes from COVID-19 would be very small. However, if it has been more than 5 months since a previous dose or infection, getting a fall booster in the next few months can help protect ourselves and our communities with the additional boost of infection prevention in the several months immediately following that dose. This is particularly relevant for healthcare workers or others who are regularly in close contact with those at high risk of severe outcomes.

Other prevention options for high-risk individuals

Whatever vaccine decisions people make, it is important to remember that there are also early treatment and prevention options for those at highest risk of severe outcomes. For example, Evusheld™ is a type of 'borrowed immunity' that can give extra protection for about 6 months to immunocompromised individuals who may not be able to fully generate their own antibodies against COVID-19 after vaccination or infection. Evusheld™ can be given to those who have had COVID-19 vaccination and can also be used in those for whom vaccines are contraindicated. Albertans wishing to access Evusheld™ are asked to speak with their doctor about whether they may be eligible.


More than 2 years into the pandemic, we continue to learn as the virus evolves and we develop more options to protect ourselves and our communities. We do not know exactly what type of variant we will be facing this winter, but with all the information we have right now, it is clear that vaccines remain an important layer of protection, especially for those at higher risk of severe outcomes. Getting both COVID-19 and influenza vaccines are wise ways to protect ourselves and our communities.


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  2. Miller, J. 2022. Booster Doses of Moderna COVID-19 Vaccines in Adults, Adolescents and Children. ACIP meeting materials. Sept 1. Slides 21-22 (PDF, 948 KB)
  3. Amirthalingam G, et al. 2021. Serological responses and vaccine effectiveness for extended COVID-19 vaccine schedules in England. Nature Communications. Dec 10;12(1):7217
  4. Skowronski DM, et al. 2022 Two-dose SARS-CoV-2 vaccine effectiveness with mixed schedules and extended dosing intervals: test- negative design studies from British Columbia and Quebec, Canada. Clin Infect Dis. Apr 19
  5. Carazo S, et al. 2022. Protection against Omicron BA.2 reinfection conferred by primary Omicron or pre-Omicron infection with and without mRNA vaccination. medRxiv. Jun 27
  6. Higdon, M, et al. 2022. Duration of effectiveness of vaccination against COVID-19 caused by the omicron variant. The Lancet Infectious Diseases. Published online June 22, 2022
  • Dr. Deena Hinshaw

    Dr. Deena Hinshaw

    Dr. Deena Hinshaw was Alberta's Chief Medical Officer of Health from January 28, 2019 to November 14, 2022.