Haven’t received the latest COVID-19 vaccine? You might want to reconsider
Researchers from the Institute for Pandemics and the Centre for Vaccine Preventable Diseases found that neither vaccine-induced, infection-induced, or hybrid immunity to COVID-19 lasts forever
By Tedd Konya and Ishani Nath
With the holidays around the corner, many people will be attending large indoor gatherings — and with the rising number of COVID-19 cases caused by highly contagious variants, those gatherings can put people at risk for infection. A new study shows that even if Canadians got previous COVID-19 vaccines or were infected in the past, it is still important to get the latest updated COVID-19 vaccine to stay protected against the virus as it continues to evolve.
“COVID-19 vaccines, experience of a COVID-19 infection, or their combination, commonly referred as ‘hybrid immunity’, teaches the body to fight off the virus, but we're learning that such protection does not last forever,” says Nelson Lee, Director of the Institute for Pandemics (IfP), the lead author of a new research published in Clinical Infectious Diseases.
The study was conducted by researchers across Ontario, Canada, including from the Institute for Pandemics and the Centre for Vaccine Preventable Diseases (CVPD). Researchers looked at how well COVID-19 vaccines and/or a previous infection protects adults over the age of 50 against Omicron-associated severe outcomes, hospitalization or death, from January 2022 to June 2023.
The results show that as the XBB virus variant emerged, the individuals studied were not as protected against COVID-19 death and hospitalization. Researchers also noted that protection begins to fade six months after an individual’s last COVID-19 vaccine dose, but it can be restored with an updated vaccine which covers newer Omicron strains. According to national data, as of December 1st, only 3.4% of the Canadian population has been vaccinated in the past six months according to recommendations, which includes the most recent updated vaccine booster.
The study further showed that although ‘hybrid immunity’ tends to last longer, it also does not provide strong protection against newer variants, and previous infection alone offers little protection. The researchers conclude that neither vaccine-induced, infection-induced, nor hybrid immunity provide long-lasting protection against severe COVID-19 outcomes as SARS-CoV-2 continues to evolve.
The reason that some infectious diseases require boosters, while others do not, comes down to the individual pathogens causing the disease, explains Jeff Kwong, senior author and Associate Director of the CVPD. “Some pathogens tend to be more stable while others are constantly evolving, and the ones that are constantly evolving, such as SARS-CoV-2 and influenza, keep us on our toes because they can evade the immunity that our bodies have developed through vaccination or prior infection,” says Kwong. “That’s why we need to get influenza vaccines every year, and why we may need to get COVID-19 vaccines once or twice per year moving forward.”
Other studies have also shown immunity wanes over a period of time but this study provides new data on Omicron subvariants and looks at a longer period (15 months) since the last vaccine dose. These findings support the approach to review vaccine composition based on continual surveillance and offer booster doses periodically, especially for high-risk individuals, alongside other health recommendations.
Kwong, who is also a family physician in Toronto, emphasizes that COVID-19 vaccines are generally very safe and the risk of serious side effects is small. By contrast, he says that “[COVID-19] infections commonly lead to all kinds of serious complications and repeated infections likely increase the risk of long COVID.”
The study reiterates the importance of continuing to get vaccinated as updated COVID-19 vaccines and boosters become available.
As the holiday season approaches, Lee says these findings are a good reminder to get the latest COVID-19 vaccine to stay protected. “Regardless of whether you’ve been infected with COVID-19 or have received previous vaccination doses, or both, immunity doesn’t last forever,” he says. “People should consider getting the updated vaccine if it has been more than 6 months since their last vaccination or infection.”