Understanding vaccine safety

 

In the first instalment last week, we discussed whether Covid-19 vaccines were effective and what that meant.

In this segment, we’ll discuss the safety of Covid-19 vaccines. However, we need to first understand how safety is being assessed and measured for medications and vaccines.

Safety of a medication or vaccine is measured through two methods: i) short-term safety; and ii) long-term safety. In this instalment, we will cover short-term safety.

What does short-term safety mean? It means that when you are taking the medication or receiving the vaccine, you do not get an effect which is not part of the intended effects of the medication or vaccine. For example, taking a Covid-19 vaccine is intended to stop you from getting symptomatic or severe diseases. That is the intended effect of the vaccine.

However, certain individuals may experience unintended effects from taking a vaccine. These effects can be divided into two: i) adverse events; and ii) side effects. Many people often mix these terms up, so it is worth explaining in more detail what these terms mean since they mean quite different things.

An adverse event is an undesired effect that occurs from getting a medication or vaccine at the proper dose. These adverse events can be a Type A reaction or a Type B reaction.

Type A reactions are predictable and usually dependent on the dose of medication given; with its reactions being mild, moderate or severe. Stopping the medication will usually bring an end to these problems. Type B reactions, however, are completely unpredictable and are usually influenced by patient factors such as drug allergies or intolerance.

A lot of concern has been raised pertaining to individuals with allergies when it comes to Covid-19 vaccines as worries abound on whether they will get a Type B reaction to the vaccine.

The US Centre for Disease Control and Prevention is tracking these data; and so far only 2-5 people for every one million (that’s about 0.000002%) are showing severe allergic reactions (or anaphylaxis) when given the Covid-19 vaccine. Detailed information is available here: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/adverse-events.html

On the other hand, a side effect is an undesired effect that occurs when a medicine or vaccine is given to an individual irrespective of the dose of the medicine being given. An example of this is taking 20 tablets of adult paracetamol or Panadol. You are not supposed to take this medication at such doses and when taken, you get side effects of acute poisoning with liver damage.

Side effects are effects that are already known (from when the drug or vaccine is tested in clinical trials) and then the patient is told to be aware of them while on medication or after being given a vaccine. Side effects usually resolve on their own over time.

Interestingly, some medications are even utilised for their side effects. One example of this is the drug mirtazapine, which is used to treat depression and some related disorders. The drug has a side effect of causing weight gain. So, it is actually used to treat anorexic patients just for this beneficial side effect.

Other common drugs which are being studied for their beneficial side effects include aspirin, which is used as a “blood thinner” and prescribed to many people to prevent them from getting heart attacks. Ongoing studies are now looking to see whether it has another beneficial side effect where a protein activated by aspirin may restrict the growth of cancer cells for certain cancers.

Another common drug that many of us take is metformin, prescribed for many of us to control our blood sugar and a mainstay of diabetes treatment. Ongoing studies are now looking to study a beneficial side effect of metformin which may be used to reduce the risk of breast cancer.

Many people ask this question: If we already know that a medication or vaccine has these kinds of side effects, why are we approving it for use by patients? The answer for this is simple, and really is about the possible benefits far outweighing the possible issues from side effects.

Simply put, taking the vaccine may cause some temporary side effects, but confers on you the protection of not getting a severe form of Covid-19 which has a much higher chance of killing you or causing long-term effects that may last a lifetime. Should we even be thinking about it?

Next up: Long-term safety profiles of Covid-19 vaccines and how we are tracking this globally

INFOVAX is a community education and awareness series on Covid-19 vaccines brought to you by the Malaysian Medical Association Public Health Society (MMA PHS). Feel free to ask questions and clear your doubts about Covid-19 vaccines by putting them to us at infovax21@gmail.com. Your questions and answers will be collated and answered in the following sessions. 

-FMT