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COVID-19 case counts in Canada and also other countries are on the rise yet again, prompting some experts to claim to be in a summer wave. Additional booster doses beyond the first booster dose are currently being offered by some countries (i.e., 4th dose to older adults and 5th dose for immunocompromised ones). As infections climb, several provinces are beginning to expand their eligibility requirements for 4th doses of the COVID-19 vaccine. Ontario's COVID-19 test positivity climbs as new details of 7th wave emerge with report of more deaths related to the virus and rising numbers of hospitalizations and ICU admissions. The biggest jump was among children aged 0-4, with cases in that group spiking by 40 %. Case rates remain higher among those 20 and over and are still highest among those 80 and up. Ontarians between 18 and 59 years old who had a first booster shot at least 5 months ago will be able to book an appointment get a second one.

WHO, with support of the Strategic Advisory Group of Experts (SAGE) on Immunization and COVID-19 Vaccines Working Group, is reviewing emerging evidence on need for and timing of an additional vaccine dose. SAGE is continuously reviewing literature and has reached out to vaccine manufacturers, research community and Member States to obtain the most complete and recent data on the issue. Health authorities’ guidelines offer Covid booster vaccine to those aged 50 and over this autumn to top up their immunity and reduce risk of becoming severely ill. The updated advice from Joint Committee on Vaccination and Immunisation (JCVI) advises governments in England, Scotland, Wales and Northern Ireland to offer booster to:

  • All aged 50 and over

  • Health and social care staff

  • Carers over the age of 16

  • Greater health risk people including pregnant women

  • Sharing house with someone with a weakened immune system

Drug companies have been developing updated vaccines to tackle newer variants; however, it is still uncertain which vaccine will be used. The details of the rollout have not been confirmed, however, it is thought immunisation will start with the oldest and most vulnerable from September.

Analysis for booster doses

Main reasons why COVID-19 vaccine booster doses may be needed can be evaluated as:

  • Declining protection against infection or disease over time such as waning immunity

  • Decreased protection against variant(s) of concern (VOC)

  • Insufficient protection from currently recommended primary series for risk groups for which evidence from the Phase 3 clinical trials may have been lacking

The rationale for booster doses may differ by vaccine product, epidemiological setting, risk group, and vaccine coverage rates. With widespread transmission of Omicron globally, continued viral evolution with emergence of new variants is already being seen. Hence, the composition of currently available COVID-19 vaccines may need to be updated to offer better protection against new VOCs which may be antigenically distinct.

Health authorities believe the application of booster doses should be evidence driven. The decision to recommend a booster dose is complex and hence, requires specifically a consideration of national strategic and programmatic aspects, and crucially an assessment of the prioritization of globally limited vaccine supply. The duration of vaccine-induced protection is likely to depend on variables such as the vaccine product, primary vaccination schedule, age, primary medical conditions of the vaccinee, risk of exposure, and circulation of specific variants. In light of this knowledge, prioritization should be given to the prevention of severe disease condition.

Global scenario related to Omicron and need for second booster

As Omicron has been designated a Variant of Concern, few actions WHO recommends countries to undertake, including enhancing surveillance and sequencing of cases. A new version of Omicron, BA.5, is now responsible for more than half of new infections in U.S. It is believed this virus is different enough from the original version—and even from previous versions of Omicron—that the vaccines and booster shots everyone has been getting are less effective against BA.5. Plus, any immunity that people generate, whether after getting vaccinated or infected naturally, wanes after few months.

Introducing booster doses should be firmly evidence-driven and targeted to the population groups in greatest need. The rationale for implementing booster doses should be guided by evidence on waning vaccine effectiveness, in particular a decline in protection against severe disease in the general population or in high-risk populations, or due to a circulating VOC. WHO is carefully monitoring the situation and continues to work closely with countries to obtain the data required for policy recommendations.

When should one get a second booster- now or wait?

There's no simple answer to that should one wait to get or right away receive their 4th COVID-19 vaccine dose. Additional doses of the COVID-19 vaccines received after completing the primary series are called booster doses, which are important as protection from a primary series decreases over time. Booster doses increase protection by activating immune response to restore protection that may have decreased over time. Boosters may also reduce the risk of post COVID-19 condition. Health authorities highly recommend a second booster shot to any one immunocompromised or over age 60. People are considered to be moderately or severely immunocompromised or have a weakened immune system due to several types of conditions such as undergoing cancer treatment, received organ transplant, taking medicine to suppress immune system, Active treatment with high-dose corticosteroids or advanced or untreated HIV infection.


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