Over 50 million people worldwide have been infected with the novel coronavirus, and over 1 million people have died. Effective, safe vaccines will be an important public health tool in preventing further loss of life. It is however not the be-all end-all, and we will have to keep doing what has been shown to be effective in limiting spread, like physical distancing, wearing a mask, staying home when ill, and washing hands often. Some of these infection prevention habits are relatively easy for some, but sometimes there are unbearable emotional and economic sacrifices.
Frankly, vaccines may not always be 100% effective in doing what we would like them to do, but they have been effective enough to help us eliminate or significantly reduce a number of terrible infectious diseases over the decades, saving millions of lives. For example, although I received the measles-mumps-rubella vaccine as a child, I did get a mild case of mumps, but we must admit that mumps, like polio, are not that common anymore.
What is mRNA?
Prior to the recent emergency use authorisation of a COVID vaccine, there has been no vaccine made from mRNA that has been licensed for widespread clinical use. mRNA or messenger ribonucleic acid/messenger RNA is, simply put, similar to your DNA – your genes that determine what you look like. The authorised COVID vaccines introduce mRNA that tells the body to make a specific part of the COVID virus called the attachment spike – the part the virus uses to attach to and cause infection in the body. Your body then sees these spikes and makes antibodies that will stick to and counteract the spikes on actual live virus that you may come in contact with in the future, thereby protecting you from infection and from COVID. It is a lot easier to make a piece of gene that codes for a small part of a virus than it is to grow live virus and then have to inactivate the virus so it becomes harmless, and then package that as a vaccine. This is what we have been doing when making vaccines up to now. For example, the flu vaccine: we grow live influenza (flu) virus in chicken eggs and harvest them, and that is a process that takes a long time. There are other mRNA and non-mRNA vaccines being investigated, including nearly 50 in clinical trials, and over 160 in pre-human trials. mRNA-based technology has allowed the rapid production of a highly effective vaccine against the novel coronavirus that causes COVID.
What is the right immune response for protection?
There is a particular graph that stands out in one of the scientific publications on the Moderna vaccine – one of the COVID-19 vaccines that is going through the approval process. The researchers looked at the type of immune responses seen in unvaccinated persons who had had COVID and recovered. It is clear that the type and quality of immune responses vary significantly from person to person, with some persons showing no or little antibody response, some persons falling somewhere in the middle, and a few persons having really robust antibody responses. In stark contrast, persons who received the Moderna vaccine all showed very robust antibody responses.
Figure. Immune responses in persons receiving the Moderna COVID vaccine in a Phase 1, dose-escalation clinical trial and unvaccinated persons who recovered from natural infection with the novel coronavirus. (Adapted from The New England Journal of Medicine 383;20)
Whether the COVID vaccine is safe for persons who have already had COVID is an important question, yet some clinical trials actually exclude such persons. For other viruses like dengue, it is well known that antibodies produced to one strain of dengue can make infection with another strain (or from vaccination, speculatively) result in worse disease and greater risk of dying. So far, fortunately, analyses of the type of immune responses elicited by vaccination do not seem to raise any immediate flags around this issue.
The elderly came out strong
One of the more surprising but welcome findings is the robust immune response in older persons. Ageing affects the entire body, including the immune system, which means that the body’s ability to mount an immune response to germs or to vaccines is significantly reduced with advanced age. For the vaccine against the flu, for example, there are formulations for the elderly that contain about a 4-times higher vaccine dose to try to get the same response and protection as younger persons. It is therefore quite remarkable that at least one of the mRNA COVID vaccines is just as good at protecting older persons from infection as it is for younger persons – 95% effective across all age groups overall, and more than 93% effective in persons over 55 years of age in a Pfizer vaccine study.
What is just as intriguing is that older persons tended to have less severe reactions to the vaccine than younger persons. For example, 78% of persons 16-55 years old had reactions at the injection site like pain or redness, compared to 66% of persons over age 55 years. The most common systemic side effects reported were fatigue, headache, muscle pains and chills, which also tended to occur less in persons over 55 years, but a growing number of allergic type reactions raises concern. The COVID vaccine is highly effective in preventing infections in the elderly, who are most at risk for severe disease and dying from COVID.
COVID vaccines are new. The technology for producing them is relatively young. Although side effects and adverse effects reported to date have been mostly relatively mild to moderate, only observation over time will reveal any true safety concerns that may exist, especially as more people get vaccinated. COVID is claiming lives worldwide every day, and safe, effective vaccines definitely improve our ability to save lives.