Highlights of COVID-19 Vaccine


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i Everyone,

Here is some highlights from my hospital’s ID and pharmacy department about COVID-19 vaccination.

Pfizer Covid Vaccine Series:  2 doses, 21 days apart

The Pfizer Vaccine was approved under an EUA. What is an EUA?  Emergency Use Authorization.  This means that it is technically not approved by the FDA by the usual means/methods.  The process and rationale as it pertains to the COVID-19 vaccine is explained here.

What kind of vaccine is the Pfizer vaccine?  It is an mRNA vaccine.  It contains no live coronavirus and will not cause COVID-19.


How many people were in the study?  So far we have data from 38,000 people, approximately half (~19,000) received the vaccine and half placebo.


How long have study participants been followed?  Data has been reported for a median timeframe of 2 months after the 2nd dose was administered


How effective is the vaccine?

·         The vaccine showed a 95% efficacy at Day 7 after Dose 2 (this is based on a finding of 8 COVID-19+ cases in the vaccine group, compared to 162 COVID-19+ cases in the placebo group).

·         Results based on subgroup analysis for age/race/sex/high-risk comorbidities all still resulted in viral efficacy at least greater than 89.3%.

·         The onset of protection after vaccine administration becomes apparent at approximately 14 days after Dose 1, which can be seen in the graph below.  After Day 14 COVID-19 cases steadily accumulated in the placebo group (red line), while remaining virtually flat after vaccine (blue line).

What type of protection does the first dose (of the 2-dose series) provide?

·         During the 21-day timeframe between Dose 1 and Dose 2 there is an estimated 52.4% viral efficacy.

·         If you were only to receive Dose 1 (and never receive Dose 2), there is an estimated viral efficacy of 82%—but this was not a primary outcome of the study, and purely theoretical/extrapolated.  (Based on 50 cases of COVID-19 in the vaccine group, compared to 275 cases in the placebo group after only 1 dose).

·         Overall, the vaccine elicited higher antigen-binding and neutralizing responses in participants < 55 years old than in older participants >55 years. The boost effect after receiving Dose 2 was most pronounced for older participants (>55 years).

·         It is not recommended to only receive one dose of the vaccine.

How long does immunity last?  Will I have to get a COVID vaccine yearly?  It’s too early to tell given we only have ~2 months of follow-up data. 

Safety & Side Effects

·         Most systemic events were mild or moderate, arose within the first 1-4 days after dosing, and resolved within 1-3 days of onset.

·         Below are 2 charts displaying the most common side effects (Fever, Fatigue, Headache, Chills, Vomiting, Diarrhea, Muscle Pain, Joint Pain) within 7 days of administration of Dose 1 (top row) and Dose 2 (bottom row).  The different colors on the bar describe how many people had mild-moderate-severe symptoms.

·         The first chart is for younger patients <55 years, and the 2nd chart for those >55 years old.  Older patients experienced lower rates of side effects.

·         Data shows that reactions after the Dose 2 are more common/pronounced than after Dose 1.

·         These results show that the vaccine can have a relatively high “reactogenicity”— the physical manifestation of the inflammatory response to vaccines.  Meaning your body produces a strong immune response to the vaccine—which is a good thing!  Unfortunately it also means you may feel unwell for up to a few days as your body is doing what it is supposed to do.

Are there any serious side effects worth mentioning?

·         In the median 2 month follow up, of all reports of severe reactions after vaccine administration, there were 3 events that investigators deemed related to the vaccine: 1 each of shoulder injury related to vaccine administration, ventricular arrhythmia, and lymphadenopathy.

·         There were a total of 12 participants with serious events of appendicitis: 8 in the vaccine group and 4 in the placebo group. None of the cases were assessed as related to the vaccine by the investigators, given an observation of 12 appendicitis cases across both treatment groups is not greater than would be expected based on prevalence rate in the US.

·         This is all based on a relatively small population (as compared to the global population).  As more and more people receive the vaccine and time goes on, trends in side effects may become more apparent.  These reports are purely based on what was shown in the study population (~19,000 people who received vaccine) for the median 2 month follow-up.

·         For example, in the study population no patients experienced an immediate allergic reaction after receiving the vaccine, however last week there were two healthcare workers (who had a baseline history of severe allergies/anaphylaxis) that developed symptoms of an anaphylactoid reaction after receiving the vaccine. Since then it has been recommended not to administer the vaccine to patients who have a history of any vaccine allergy.

What are the long-term side effects?   We only have data for ~2 months post-dose, so it is impossible to know at this point.


The following information comes from the CDC for recommendations in special populations :


Pregnant women

·         There are no data on the safety of COVID-19 vaccines in pregnant women

·         Animal developmental and reproductive toxicity studies are ongoing

·         Studies in humans are ongoing and more planned

·         mRNA vaccines are not live vaccines and are degraded quickly by normal cellular processes and don’t enter the nucleus of the cell

·         Pregnant patients may be at an increased risk of severe illness due to the COVID-19 disease (ICU admission, mechanical ventilation and death), and of adverse pregnancy outcomes (preterm birth)

·         If a woman is part of a group (e.g., healthcare personnel) who is recommended to receive a COVID-19 vaccine and is pregnant, she may choose to be vaccinated. A discussion with her healthcare provider can help her make an informed decision.

·         Considerations for vaccination: – level of COVID-19 community transmission, (risk of acquisition) – her personal risk of contracting COVID-19, (by occupation or other activities) – the risks of COVID-19 to her and potential risks to the fetus – the efficacy of the vaccine – the known side effects of the vaccine – the lack of data about the vaccine during pregnancy

·         Pregnant women who experience fever following vaccination should be counseled to take acetaminophen as fever has been associated with adverse pregnancy outcomes

Breastfeeding/Lactating women

·         There are no data on the safety of COVID-19 vaccines in lactating women or the effects of mRNA vaccines on the breastfed infant or milk production/excretion

·         mRNA vaccines are not considered live virus vaccines and are not thought to be a risk to the breastfeeding infant

·         If a lactating woman is part of a group (e.g., healthcare personnel) who is recommended to receive a COVID-19 vaccine, she may choose to be vaccinated

Persons with a history of SARS-CoV-2 infection

·         Vaccination should be offered to persons regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection

·         Data from phase 2/3 clinical trials suggest vaccination safe and likely efficacious in these persons

Persons with known current SARS-CoV-2 infection

·         Vaccination should be deferred until recovery from acute illness (if person had symptoms) and criteria have been met to discontinue isolation

·         No minimal interval between infection and vaccination.  However, current evidence suggests reinfection uncommon in the 90 days after initial infection and thus persons with documented acute infection in the preceding 90 days may defer vaccination until the end of this period, if desired

Persons who previously received passive antibody therapy for COVID-19

·         Currently no data on safety or efficacy of COVID-19 vaccination in persons who received monoclonal antibodies or convalescent plasma as part of COVID-19 treatment

·         Vaccination should be deferred for at least 90 days to avoid interference of the treatment with vaccine-induced immune responses

·         Based on estimated half-life of therapies and evidence suggesting reinfection is uncommon within 90 days of initial infection

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