Ask the Pharmacist: How do vaccines differ?

Q) I understand there have now been three more vaccines approved for use in Canada in addition to the Pfizer and Moderna versions. What can you tell me about them and how do they differ from the first two?

A) Actually, while the original press release made it sound like there are three new vaccines, in fact there are only two.

The AstraZeneca (AZ) vaccine developed in conjunction with Oxford University in the United Kingdom is identical to the vaccine whose trade name is Covishield. The only difference is this name is used to identify those lots of the vaccine manufactured by the Serum Institute of India since AstraZeneca uses multiple manufacturing sites throughout the world for their vaccine.

The other new option is produced by Johnson & Johnson (J&J) and it was just approved for use in Canada on March 5th, roughly a week after the United States did so. There is in fact, a 5th vaccine being studied by Health Canada called Novavax but its approval is still weeks to months away, if all goes well.

So, let’s turn to the two new entries and discuss what makes them different.

For one, they use a different technology to induce immunity than the first two which relied on the novel mRNA process. These are both known as viral vector type vaccines, as is the Russian COVID vaccine known as Sputnik V. Viral vector vaccines use another harmless virus as a sort of vehicle to deliver a small portion of the SARS-COV-2 virus. Basically, a small portion of this carrier virus gets replaced with some of the genetic information of the SARS-COV-2 virus that causes it to produce the distinctive “spike” proteins.

As we know from centuries of existence, viruses are very efficient at entering into our cells and using the machinery there to reproduce. Traditionally, this leads to infection and subsequent antibody production. In this case, since the virus has been modified, once it is injected into our arms it travels to our cells and induces our cells to make this same “spike” protein from the genetic information it received without making the rest of the virus. Our immune system recognizes these spiked cells as not belonging to our body (i.e. foreign) and, in response, it begins producing antibodies and activating other immune cells to “fight off” what it perceives to be an infection. The end result is that our body has a ready-made defence against the COVID-19 virus before it ever encounters it.

This type of technology has been used for years in gene therapy and in the creation of the vaccine that protects against the Ebola virus. Viral vector vaccines have the advantage of being both easy and cheap to make, which is critical when looking at vaccinating millions of people in as short a time as is possible without completely breaking your budget.

Their disadvantage is that some of us have antibodies in our system already from past colds that may target the vaccine thereby making it less effective. This may be why the “numbers” are lower for the AZ and J&J versions. Whereas the mRNA vaccines are over 90% effective in preventing disease, both of these are significantly lower. The J&J version is believed to be at 66% and the AZ may be at 62%.

Before you go insisting on an mRNA vaccine that you may well have to wait for as supplies are limited, (although Canada received some rare good news on this front on March the 5th in that 1.5 million more Pfizer doses will be delivered this month and another 2 million that were set to arrive in the summer will instead be delivered in April & May. Hurray!!) keep in mind that these are not head-to-head comparisons. These trials were done in different populations, with different end points and perhaps differing viral variants circulating around.

An end point is the main result being looked for i.e. death, infection, hospitalization etc.. As such, it is impossible to know for certain, at this point, which vaccine is the most effective. What is known is that all four options are safe and work far better than nothing, which is critical when a third wave of the pandemic is expected almost any time now.

The two new options are extremely effective against severe COVID-19 infections. In clinical trials, the AZ version was 100% effective in preventing hospitalization or death from COVID and the J&J version was at least 85% effective in doing this. Most of us do not mind getting a little sick, we just don’t want the course of the rest of our lives to be affected when it happens.

All four of the vaccines appear to accomplish this by limiting the damage to our body. They all seem equally safe as well from an adverse reaction standpoint. There is ongoing debate as to whether the AZ version should be used in those over the age of 65 due to mixed messaging from the government and the National Advisory Committee on Immunization (NACI). Health Canada approved the vaccine for all people 18 and over (AZ is currently conducting a study on its use in kids 6 to 17 years of age), whereas the NACI recommended it be reserved for those who are under the age of 65. This is due to a lack of data in the trials about using the AZ vaccine in our oldest seniors. However, real world data in the U.K. seems to prove it is both safe and effective above the age of 65.

This has caused countries such as France and Germany, which were initially in agreement with the NACI, to change course and approve it for all adults. Perhaps the best thing about these two new vaccines is that they are much more stable meaning that they can be stored in a fridge for up to three months rather than requiring the use of an ultra-cold freezer like the Pfizer vaccine. This will really help facilitate the rapid distribution of vaccines into easily accessible venues such as community pharmacies.

In fact, there are 380 or so pharmacies in the Toronto, Windsor and Kingston areas that will receive the AZ vaccine this week and start injecting it into the arms of adults aged 60 to 64. If this pilot project proves successful, it should be sooner rather than later that the various pharmacies along the shores of Lake Huron will be included.

The last significant difference applies strictly to the J&J vaccine. It is a unique COVID vaccine in that it requires only a single dose, much like the annual flu shot. This takes away any debate as to how long to space booster doses or the like. This will greatly decrease the costs to our economy due to the massive manpower it takes to administer vaccines to millions of people and the loss of productivity as people take time off from work to receive a second dose. It also lessens the worry about the many people who forget to receive their booster dose or decide to forgo it as the pandemic becomes less and less prominent in our lives (hopefully!!!).

With the other vaccines, there is a decent chance their immunity will fade in short order allowing them to be susceptible to a virus that is likely here with us to stay. For more information about this or any other health related questions, contact your pharmacist.