Omicron Variants: CDC Finds Fourth Dose Increases Protection Against COVID

Thinking about whether a fourth dose will help keep you from contracting COVID-19? Here's what a recent study run by the CDC revealed about Omicron variants.

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A second booster shot of an mRNA vaccine is significantly effective in warding off severe illness that some Omicronn variants can trigger, a study by the U.S. Centers for Disease Control and Prevention (CDC) examining the effectiveness of fourth doses of COVID-19 vaccines has found.

More than 200,000 emergency department visits and 58,000 hospitalizations with COVID-19 were analyzed in the study, which looked at effectiveness against Omicron BA.1 and BA.2/BA.2.12.1. 

BA.4 and BA.5 are more recent strains that are thought to be predominant among the current wave of COVID-19 cases in Canada and other areas and were not part of the study. 

After an individual has had a first booster shot, the study found that the effectiveness of the vaccine against severe illness with Omicron variants BA.1 and BA.2/BA.2.12.1 was found to be just 68 percent in the first six months. That figure dropped to 52 percent after this point.

However, after a second booster shot, the CDC found the effectiveness against severe illness with the variants mentioned above increased to 80 percent during the first six months. No data about the effectiveness of a fourth dose of the vaccine after the first six months are available.

Hospitals and emergency departments also saw fewer visits related to BA.1. and BA.2/BA.2.12.1 from people who had had fourth doses. 

According to the CDC, this is one of the first reviews of the impact of second booster shots when fighting Omicron variants. 

Based on these findings, it's safe to say that if you are eligible for a second booster, you may want to strongly consider getting one to bolster your protection against the virus and potentially help reduce the need for a visit to the emergency department related to COVID-19, leaving hospitals and healthcare resources more available for those who need them. 

In Canada, many provinces and territories are offering second booster shots to vulnerable populations including the elderly or immunocompromised. Some regions have expanded that eligibility to include more groups from the general population. 

The report from the CDC was published Friday, July 15 in their Morbidity and Mortality Weekly Report. Data from 10 states and 19 institutions was used, including academic organizations and public and private clinical and research organizations, between December 2021 and June 2022. 

The odds of hospitalization or emergency department visits between those vaccinated with one, two, three or four doses in addition to those who were completely unvaccinated, were used to determine the effectiveness of the vaccine. 

After a fourth dose, vaccine was 80 percent effective in preventing hospitalization with COVID-19, while vaccine effectiveness against visits to the emergency room increased from 32 percent after the third dose to 66 percent after fourth doses.  

Previous COVID-19 infections were not factored into data from patients, but could have impacted their immunity. 

While the variant patients had was not confirmed via lab testing, they sorted them based on timing of when patients tested positive and which variants were known to be dominant (comprising more than 75 percent of cases) in that region during that time period. 

Fourth Dose Eligibility 

UPDATE: The Government of Ontario has expanded eligibility for fourth doses to offer an extra layer of protection against both the Omicron BA.1 and BA.2 variants. As of July 14, 2022, populations eligible for a fourth dose include:

  • Adults aged 18 to 59 who had a third shot at least five months ago (or have been free from COVID-19 infection for three months)

Previously, eligibility was restricted to:

  • Individuals aged 60 years and over at the time of vaccination. 
  • Anyone who identifies as a First Nation, Inuit or Métis and their non-Indigenous household members aged 18 years and over at the time of vaccination. 

Get Your COVID-19 Test 

You might consider coupling your fourth dose with COVID testing for peace of mind, or if you require a COVID-19 test for travel. We can schedule your RT-PCR Test or Antigen Test, or answer any questions you may have about COVID Certificates. 

To learn more about safe travel or to schedule your COVID-19 test prior to traveling, contact a COVID Travel Test location near you.

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