Vaccination against COVID requires side effects of vaccines are scrutinized very closely. Would we be more reassured if the number of side effects were zero? A scenario that is unlikely to occur.
Most of the side effects seen so far with these vaccines are the same as with the flu shot: injection site pain, headache, fatigue, chills, nausea, weakness, fever, dizziness, sore muscles, increased heart rate.
Even with a placebo
However, it should be remembered that even placebos “cause” side effects. During the Pfizer / Biotech vaccine clinical trials, those who received a first injection of saline water reported fatigue (33.4% against 47.4% in those who received the vaccine), headaches (33.7% against 41.9%), chills (6.4% vs. 14%), vomiting (1.4% in both categories), diarrhea (11.7% vs. 11.1%), and muscle pain (10.8% vs. 21.3%).
This is called the effect nocebo. One more person expects to have effects (positive – placebo effect, or negative – nocebo effect), the more likely it is. Thus, patients who anticipate side effects may suffer from them, even if they only receive an injection of saline water or a sugar pill.
In a review of 31 studies published in 2012 and reported in the New York Times, German researchers found that several patients had dropped out of clinical studies because of the side effects, even though they were receiving the placebo. Among the causes mentioned: anticipation of adverse effects, previous experiences associating medication and symptoms, attributing to the treatment received discomfort felt by pure coincidence in the days that followed, or anxiety. All of this can cause patients to be so on the lookout for side effects that they will feel them, or think they are feeling them.
This nocebo effect may also occur in patients who receive the real vaccine, making it difficult to distinguish between minor side effects caused by the vaccine and those caused by anticipation and anxiety, thus skewing the data on side effects of drugs.
More serious side effects
This is not to minimize the side effects which are more serious and which cannot be attributed to a placebo. The most serious is anaphylactic shock, an allergic reaction that can be fatal. The Center for Disease Control and Prevention (CDC) in the United States listed in its first review of the vaccination campaign 21 anaphylactic shocks among the first 2 million doses of Pfizer vaccine distributed before the holidays. In one with second (released February 12) extending through January 18 and covering the vaccines from Pfizer and Moderna, there were 66 anaphylactic shocks in 18 million doses, a rate of 3.6 per million (or 0, 00000003%). In comparison, the flu vaccine generates an average of 1.3 anaphylactic shock per million doses administered. Polyethylene glycol, a compound in the lipid “capsule” that carries the vaccine, has been mentioned as possible suspect to explain this difference.
No one has died from side effects related to the vaccination campaign in the United States, and as of January 18, 32 of those 66 people had required hospitalization.
However, countries are closely monitoring the adverse effects of vaccines on their populations. A pan-canadian study with one million patients, which will analyze the side effects of COVID-19 vaccines, was launched in January.