A word about booster shots:
When COVID-19 vaccines started to be rolled out a year ago, some of you may remember that there was already uncertainty regarding how long the vaccines would protect us and whether we would need additional shots down the road.
Now that a year has passed, we are largely able to answer some of the key questions below about the protection vaccines give you and why you should get your booster:
1. How long does immunity to SARS CoV-2 last?
We have learned that immune protection from reinfection after vaccination is strong, but it doesn’t last all that long i.e it lasts for several months, not years. Similarly, immunity following infection starts to wane a few months after infection. This is similar to what we see for other coronaviruses so none of this is a big surprise. By 6 months, the protection against infection is far below what it was in the first few months.
2. Does natural infection with SARS CoV-2 provide better immunity than vaccination?
No, actually the opposite is true. Immunity following vaccination is stronger and tends to last longer than from natural infection, especially if the natural infection was mild.
3. How do viral mutations i.e. Delta, Omicron impact immunity?
We learned with Omicron that prior infection with Delta did not protect one from being infected with Omicron. We also have recently learned that after a few months after being infected with Omicron, one can get re-infected with Omicron. Prior infection though does provide some protection from getting more serious disease.
4. How have vaccines changed as the virus has mutated?
The vaccines we have received were made against the original strain that was identified in Wuhan 2 years ago. It has not been modified to specifically target the mutant strains that have subsequently developed like Alpha, Delta, and Omicron. There are a few of reasons why the vaccine hasn’t changed (yet).
a. The vaccines still protect against serious disease, although not as well against infection compared to the original strain, especially with Omicron;
b. Changing the vaccine early on would have delayed roll out leaving more people unprotected.
c. It isn’t clear which strain to make the new vaccine against—with frequent mutants emerging, the vaccine industry has needed to better understand what strains need to be targeted.
It is clear though that at some point this year, it is very likely that vaccines will be developed against newer mutants strains.
5. Why is a third dose (booster) necessary? Given the waning immunity issue mentioned above and given that two doses only weakly protects against infection with Omicron, booster doses are necessary. Otherwise, Omicron can continue to spread widely in vaccinated and unvaccinated people, making it very hard to control spread to the unvaccinated and immunocompromised/vulnerable populations, leading to high levels of hospitalization. Studies have shown that booster doses significantly restore protection against infection and offer additional protection against serious disease.
To sum up, considering people fully vaccinated with two doses is now out-of-date thinking. It is now clear that we will require at least a 3rd doses, and likely regular booster doses in the years to come.
It is interesting to me that while we as health care workers are very highly vaccinated with our first two doses, we have been less keen on getting booster doses. So far, about 76 per cent of staff have received their booster shot, and in some areas the rates are significantly lower.
I hope this note makes it clear that those boosters are needed and that as time goes on, those people with only two doses will be less and less immune with time.
I strongly encourage those of you who are eligible to get a booster dose to go ahead and do so.
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