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Research says the second dose of COVID-19 vaccines acts as a booster shot to sustain antibodies in your system

Study shows the need for getting the second vaccine dose as quickly as possible

Public Health Sudbury and District is just one of many health units across Ontario pushing to have higher second-dose COVID-19 vaccine counts.  In the PHSD weekly update published Thursday, the health unit said having low daily COVID case counts and higher vaccine rates is the only way to move forward out of the Step-3 phase of Reopening Ontario.

In line with that thinking, the CanPath organization, the Canadian Partnership for Tomorrow's Health, a research agency, has issued a statement that said a formal national study about COVID-19 antibodies has revealed "a high-degree of variability in the level of antibodies produced by a single dose of a COVID-19 vaccine".  In many cases, the effectiveness of the first dose begins to lose strength over time. 

"These findings highlight the importance of accelerating second doses as the Delta variant continues to spread, particularly with the vast majority of Canadians having received only a single vaccine dose. This is the first pan-Canadian study using samples from a wide range of participants to confirm evidence from vaccine manufacturers’ clinical trials, as well as findings in a recent preprint from the United Kingdom and other smaller studies," said the CanPath report. 

To be accurate, Health Canada figures** show that 78.63 per cent of the population aged 12 and older received at least one dose of a COVID-19 vaccine.

At the same time, based on the Health Canada data, there are 50.04 per cent of Canadians that have received two doses and are considered fully vaccinated.  

** Data was accurate as of noon on Friday July 16, 2021.

Preliminary results, which were based on a sampling of 23,000 adults from across Canada, showed that the level of antibodies from first doses of different vaccine types had varying results, said Dr. Philip Awadalla, National Scientific Director of CanPath. Awadalla said findings also revealed that the mRNA vaccines, in single doses, provided more antibodies than the Astra-Zeneca vaccine. 

“Consistent with earlier reports, we also found that single doses of the mRNA (Pfizer-BioNTech and Moderna) vaccines produced short-term antibody levels over one and a half times greater than those produced by the viral vector vaccine (Oxford-AstraZeneca)," he said.   

The study also reported that early results showed a lag in the development of antibodies after a single vaccine dose. Through a supporting online survey, CanPath said it recorded those who had been vaccinated, the date of vaccination, and the vaccine type and name.  In the winter and spring of 2021, Canada implemented a first-dose strategy of providing vaccines to as many people as possible, as quickly as possible. The interval for second doses was stretched out to allow more Canadians to get their first dose early. 

There was praise for this idea, but now medical experts are urging Canadians to get their second dose as soon as they can. 

“The ‘first-doses-fast’ strategy adopted in Canada has worked extremely well so far in reaching more Canadians. We have seen a drastic reduction in case numbers and hospitalizations, despite the arrival of variants, allowing us to look forward to a better summer,” said Dr. Catherine Hankins,  co-chair of the COVID-19 Immunity Task Force (CITF). 

“That said, this study offers more evidence that Canadians considering only one dose need to know that they are not fully protected. Getting a second dose is vital now with the Delta variant on the rise.” 

Awadalla said studies are now indicating that it is important to get the second shot -- as a booster shot -- to sustain the antibodies in your immune system. 

“Although participants may still be protected through other immune mechanisms, these findings underscore the fact that, after a single dose, antibody production is far from what is produced after two doses,” said Awadalla. 

The study reported high levels of antibodies in participants with two doses of an mRNA vaccine, with levels almost twice as high as those after the first dose. Whereas other studies have shown waning of antibodies after single doses of mRNA vaccines, CanPath found that levels of antibodies after two doses of an mRNA vaccine appear to stabilize over a period of 95 days.

The concern in the medical community is that many Canadians could be thinking that a single vaccine dose is all they need and that many are just not bothering to get their second dose. 

Dr. Theresa Tam, Canada's Chief Public Health officer, said the CanPath study points to an important conclusion. 

“These preliminary study results reinforce the need for Canadians to get their second dose of COVID-19 vaccines. Completing a two-dose vaccine series provides stronger protection against symptomatic infection, severe illness and variants of concern including the Delta variant,” said Tam. 

“Vaccines, in combination with public health measures and individual precautions, continue to be key in reducing the spread of COVID-19," she added. 

As recently as Friday afternoon, Health Canada issued a fresh reminder encouraging Canadians to get their second dose.



Len Gillis, local journalism initiative reporter

About the Author: Len Gillis, local journalism initiative reporter

Len Gillis is a Local Journalism Initiative reporter at covering health care in northeastern Ontario and the COVID-19 pandemic.
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