Pfizer mRNA Vaccine and Reported Side Effects

Disclaimer: Although I am a medical professional, the information below is for your education only and not meant to be medical advice.  Please consult with your physician to determine if you are safe to receive any current or future vaccines involving SARS-CoV-2. 

On (12/10/2020), the CBER and VRBPAC will meet to discuss emergency use of the Pfizer vaccine in the general population (you can google the names, but basically the groups that approve vaccine use).  Prior to today (12/8/2020), we did not have access to all the data reported on the vaccine’s side effects.  However, that information packet has now been released to the general public.  Below is a quick synopsis of the data and my thoughts on it.

Before we dive in, let’s get a couple things out in the open.  Vaccines cause side effects.  Now, we must ask what a side effect is.  Is a fever a side effect?  Muscle soreness at the injection site?  Fatigue?  All these symptoms are signs of our immune system doing its job.  If you look at my last post on the vaccine, I discussed this a little more in detail.  We EXPECT to see these short-lived side effect responses after inoculation.   

I will mention this below as well, but it bears repeating.  A SEVERE adverse event after a vaccine during a vaccine trial does not mean that the vaccine (or placebo for that matter) caused the event.  People over the age of 55 have health issues like stroke, heart attack, and other complications.  This also happens during vaccine trials.  However, all events must be reported that occur during the trial, even if the event has absolutely no relation to the inoculation event.  

Requirements for the Vaccine

It has been reported that for approval of a COVID-19 vaccine, the efficacy should be >50% and any benefits of the vaccine should significantly outweigh the risks.  We already know that the reported efficacy for the mRNA vaccines have been between 90-95%, so we checked that box.  

When looking at the risks, or side effects, vaccine trials go through a series of phases.  Phase 1 and 2 trials are for serious side effects or severe COVID infection in this trial.   Phase 3 focuses on common and expected adverse reactions shortly following vaccines, as well as monitoring participants for up to 2 months for vaccine efficacy long term.  Phase 1 and 2 duration is typically longer than Phase 3.

Adverse Events (Side Effects) Data:

Comparing the data of the placebo vs treatment group,

0.4% of both the treatment and placebo group after the 1st shot and 0.3% and 0.2% respectively after the 2nd shot had immediate reactions within 30 minutes (ie soreness at the site or other mild events typical for an injection at the site).

When looking at symptoms within 7 days after injection, the treatment group had a much higher reported number of reactogenicity symptoms (your typical post-vaccine symptoms) at the injection site than placebo group (78.6% vs 12.8% with the first shot, and 73.1% vs 10.6% in the 2nd shot).  This is expected, as the body’s immune system is responding to the vaccine.  These symptoms include pain, redness, or swelling at the site, with pain being the most frequently reported symptom.  This was the same for both the 18-55 year-old group and the >55 year-old group.

In terms of systemic symptoms within 7 days (those symptoms not related to the site of the shot), the numbers were much closer together surprisingly (59.1% vs 47% after dose 1 and 69.9% vs 33.8% after dose 2 when comparing the vaccine group to the placebo group).   

In order of frequency of these symptoms from more common to less common, they include fatigue, headache, muscle pain, chills, diarrhea, joint pain, fever, and vomiting after the 1st dose in the 18-55 year-old group.  Interestingly, the placebo group also complained of fatigue, chills, diarrhea, vomiting, muscle pains, joint pains, etc, which makes one wonder if some of these symptoms reported are due to other illnesses or exposures after inoculation unrelated to the injection itself.   Symptoms after the 2nd dose increased in frequency in the treatment group, whereas it decreased in the placebo group.

The other interesting aspect with this data is that these systemic side effects within 7 days post inoculation were reported more frequently in the 18-55-year-old group when compared to the >55-year-old group, who shared the same symptoms.  

Serious Adverse Events

Let’s discuss something before we get into the numbers.   As mentioned above, If ANYTHING happens during the vaccine trial time period, these get reported as possible serious adverse events.  You will see below that appendicitis gets reported as well as heart attacks and stroke.  The general population experiences these situations without being in a vaccine trial, so having these reported does NOT mean the vaccine or placebo caused them.  However, when assessing vaccine safety, ALL cases must be reported.  Even a facial fracture was reported in the data; and no, the vaccine did not cause the bones of the face to spontaneously break.  

The big question everyone asks is were there any severe events due to the vaccine?  Let’s address deaths: 2 people in the vaccine group and 4 people in the placebo group died during the study.  This does NOT mean they died from the vaccine (or the placebo for that matter).  The causes of death were reported as a heart attack, stroke, arteriosclerosis, or 2 unreported causes in the placebo group.  Of the 6 total, 5 were >55 years of age (the 2 in the treatment group were both >55).  When reviewing the information on these deaths, it was determined that they were UNRELATED to the vaccine or placebo.

When looking at the full time period of the study (dose 1 through 1 month after dose 2), the percentage of reported serious adverse events not related to death were 0.6% in the treatment group and 0.5% in the placebo group.  The vaccine group had an increased number (by a very small amount) of cases of appendicitis, heart attack, and stroke, whereas the placebo group had an increased incidence of pneumonia, atrial fibrillation, and syncope (passing out).  So, did the placebo cause these?  Did the vaccine cause appendicitis?  Most likely not, and when reviewed by the FDA and study investigators these situations were calculated to be in comparison to the normal population and not thought to be vaccine related.  

Now, we need to include everything in the discussion here.  There were THREE events that were determined to possibly be caused by the vaccine.  One was lymphadenopathy (enlarged lymph nodes) in the patient’s axillary (arm pit) area, which self-resolved.  Our lymph nodes swell when fighting infection, so I am not sure I would truly classify this as adverse (but that is just me).  The second was an abnormal heart rhythm in a patient who already had a known cardiac condition.  The third was reported as a shoulder injury, but no other information was given


The study released was not done to include pregnant participants.  However, sometimes people become pregnant while in a study due to, well, life.  Once determined someone was pregnant, they were removed from the study.  A total of 23 pregnant participants were reported during the trial.  These participants were still monitored after removal from the study to assess for any potential side effects involving the mom or unborn fetus.  At this point there were no obvious adverse events reported in the vaccine group, however this study was NOT designed for pregnant patients, thus data can not fully be interpreted.  There was a case of spontaneous abortion and another of retained products of conception, both in the placebo group, and no reported adverse outcomes in the vaccine group.  Again, this data is not meant to be interpreted to use with pregnant patients, but I wanted to include it.

Other populations with limited data on vaccine use

Children under the age of 16 were not included in the study.  The population of 16 and 17 year old participants also only included 1 positive COVID case in the participants, so it is hard to know the efficacy in this age range; but one may assume it is similar to the young adult population in the study.

Patients with previous COVID infections prior to the study were not included, thus efficacy of the vaccine in this population was not studied.

Patients who are immunocompromised were also not a part of the study in a significant number to have appropriate data.  

Ability to transmit the virus after being vaccinated was also not studied.  No, I am not talking about making others sick from the mRNA in the vaccine.  I am talking about getting the two doses of the vaccine, developing an immunity, and then being exposed to the live virus in the community.  You may not get sick, but you could still spread it.  

My Thoughts

After reviewing this information and data, it reads like other vaccines trials.  You expect to get some symptoms after a vaccine due to your immune system responding to the foreign antigen.  However, no significantly reported adverse events were reported in high enough numbers compared to the general population to warrant a hold on its use.  At least, I assume that will be the decision come 12/10.

Do we have significant long-term data on the vaccine?  No, because the virus has only been around for less than a year.

Do we know how the vaccine affects patients who are pregnant, under the age of 16, or are immunocompromised?  No, but the study was not designed to follow this.  Some studies are underway at this point, and I am hopeful we will see more data on this as the months pass.  

In the end, I am comfortable getting the vaccine once I can get it.  I am a health care worker, so I suspect I will get it before most of the general population.  However, I am not considered high risk, so there is a chance I may get passed over due to vaccine availability.  

With that said, I understand that this vaccine trial DOES NOT study TRANSMISSION of the virus after vaccination.  Thus, even when I do get the vaccine, I will STILL WEAR A MASK, SOCIAL DISTANCE, WASH MY HANDS, AVOID CROWDED AREAS, etc, until we know it is safe to do otherwise.  

Stay healthy out there

Imperfect Dad, MD


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