Ask the Pharmacist

Q) I expect to get one of the COVID vaccines sometime in the next two months. I understand my second shot will probably be 4 months later. When will I likely have some degree of protection from this virus?

A) As of March 25th, almost two million Ontarians have received at least one dose of a COVID vaccine and 304,386 of these have been fully vaccinated having already received their second dose.

As Ontario continues to ramp up their vaccination scheduling (almost 80,000 doses were administered on the 25th) with plans to make the AstraZeneca and eventually the Johnson & Johnson vaccines even more readily available by allowing various selected pharmacies and doctor’s offices throughout the province to administer them, this is a question which will hopefully soon impact most Ontarians.

Immunity from a vaccine does not occur suddenly, as if by magic, right after receiving your second dose. In fact, the CDC in the States does not consider you to be fully vaccinated until at least two weeks after your second dose. The good news however is that long before this time, your body will start to form the defense mechanism against the virus that we call immunity and it is a process that occurs gradually over days to weeks.

This is true not only of the various COVID vaccines but also applies to all other vaccines as well. This is why we administer the flu vaccine before the flu season and travel vaccine shots at least a couple of weeks before you enter the endemic area.

Initially, not much happens after your first injection. That is why it is not surprising when you hear of people becoming infected with COVID just days after receiving their shot. The vaccine did not “cause” the infection (just as the flu shot does not cause the flu although there are some who remain utterly unconvinced of this). It is incapable of doing that. It is also, unfortunately, initially incapable of preventing the infection either, at least until your immune system “learns” to protect itself some time thereafter.

What happens is that, when you receive your first injection, the serum essentially delivers the equivalent of a set of instructions to the body. Over the next few days to weeks, your various immune cells engage in several steps designed to help it understand and act upon these “instructions”.

The first step occurs as quick-acting immune cells study the vaccine’s contents (which are modified forms of the virus that have been killed or at least greatly weakened) and carry the information back to our B cells. These are the immune cells that make antibodies and T-cells. They create these virus killing cells and teach them to zero in on the invasive pathogen with incredible precision.

As time goes on, there is even a competition of sorts that occurs between the various B & T cells such that the weaker ones are eliminated further enhancing our immune response. This whole process means that gradually, day by day after our first injection, we will have a greater and greater chance of fighting off this virus if we are exposed to it. The data seems to support this as well.

For instance, the Moderna vaccine is 92% effective, on average, 14 days after the first dose. The data for the Pfizer shot has been similarly positive. Its efficacy is believed to be 89% by days 15 to 21 after the first shot.

For the much maligned (and most of it because the manufacturer has a done an extraordinarily poor job of managing the vaccine’s roll out and clearly communicating with the general public when challenges have arisen) Astra Zeneca vaccine, its immune boosting effects were noted 14 to 20 days after the first injection and reached 60% effectiveness at the 28 to 34 day mark with slight increases noted thereafter.  NOTE: Its numbers are much higher when it comes to its ability to prevent severe disease and death even at this early stage.

As for the Johnson & Johnson vaccine, the only one of the candidates that requires just a single dose (although research is now being conducted to see if there would be any additional benefits gained by giving a booster shot of this vaccine so time will tell if it remains the lone “single-dose vaccine”), it has been found to be 67% effective after 2 weeks with the numbers rising to 72% shortly after that (these numbers are from the US, they are slightly lower elsewhere in the world).

Now, it is important to remember these numbers are an average among all people. In other words, some will not respond as robustly or as quickly as others will. For example, the range in response for the Pfizer shot varies from 52% to 97%. It is a regrettable fact that the people who are most likely to be in the lower range are also the same ones that are the most vulnerable to the virus (i.e. the very old and the immune impaired such as those already battling cancer and other disease states). It is this variation in response which is causing our vaccine experts to debate whether our most vulnerable should actually wait a full four months before receiving their second dose.

There will be lots of debate and study on this subject in the weeks to come. Regardless, the numbers don’t lie. All four of these vaccines provide very good protection within weeks of just a single dose (even in our most elderly, just check out the plunging mortality numbers in our long-term care homes despite the surge in infections) which is, at least, somewhat stress-relieving for our many health care workers and our most elderly seniors as the third wave crashes down upon us. The protection at that point isn’t nearly enough that they can discard their masks and hug long missed friends, but it seems more than adequate to keep them out of the hospital or morgue.

For more information about this or any other health related questions, contact your pharmacist.