Demystifying the Pfizer/BioNTech Covid-19 Vaccine

Q&A with CHRHS Director, Dr. Adam Levine

With a Covid-19 vaccine now being rolled out in the U.S. including here in Rhode Island, we thought it would be an opportune time to catch up with CHRHS Director and Associate Professor of Emergency Medicine, Dr. Adam Levine to help us better understand the safety and efficacy of the Pfizer/BioNTech Covid-19 vaccine. Dr. Levine's responses are in reference to the Pfizer Vaccine Study, published in New England Journal of Medicine, which you can read here. For those of you who are not familiar with Dr. Levine's work, he is intimately aware of COVID therapeutics, and is site lead on several trials including convalescent plasma and a monoclonal antibody. 

- Take Home Point -

In a large, multicenter, randomized controlled trial, the Pfizer/BioNTech Covid-19 vaccine was found to be 95% effective at preventing Covid-19, which is very good for a vaccine. Adverse events related to the vaccine were generally mild or moderate, and there was no difference in the rate of serious adverse events between vaccine and placebo recipients.

What does the vaccine involve?

Vaccination consists of two intramuscular injections given 21 days apart, in the deltoid muscle. While the vaccine starts providing some protection about two weeks after the first dose, it is only 52% effective after just one dose, rising to 95% with the second dose, so it’s important to get both doses.

How do we know it works?

The vaccine was studied in a Phase 3 randomized controlled trial of about 44,000 participants, which is the gold standard for vaccine trials. In the study, half the participants randomly received two doses of the vaccine and half the participants received two doses of saline. Just 8 people were diagnosed with a new Covid-19 infection more than 1 week after the second dose in the vaccine group compared to 162 people in the saline group, which means that the vaccine was about 95% effective at preventing symptomatic infection (a separate study will be published soon showing how effective the vaccine is at preventing asymptomatic infection). For comparison, the flu vaccines we receive each year are generally only 40-60% effective at preventing influenza, depending on the year.

The study also found that only 1 person in the vaccine group developed severe Covid-19 infection (i.e. requiring ICU admission) compared to 9 people in the saline group, suggesting that vaccination provides protection against severe disease even in the small percentage of people who are infected with Covid-19 after vaccination.

The study included both men and women, as well as large numbers of White, African American, and Latino/a patients. The vaccine worked about as well in all of these subgroups. The study included adults/adolescents ranging in age from 16-90, and the vaccine worked just as well in those over 55 as those under 55.

What are the common side effects?

The most common adverse event (or side effect), was mild to moderate pain at the injection site, which about ¾ of study participants in the vaccine group experienced after both the first and second dose. Less than 1% experienced severe pain and only 5% had any redness or swelling, which was mostly mild. About half of vaccine recipients experienced mild to moderate fatigue, and about a quarter experienced headache, chills, or muscle aches, which were somewhat more common after the second dose and generally lasted about 1-2 days. Fever was rare after the first vaccine dose, but about 16% of people under 55 and 11% of people over 55 had fever after the second dose, usually mild and resolving after 1-2 days.

What are the serious side effects?

Serious adverse events, such as those resulting in hospitalization or death, were very rare (<1%), and occurred at the same frequency in the vaccine and placebo groups, so were unlikely to be related to the vaccine. Based on the number of participants enrolled, the study would be able to detect adverse events occurring in at least 0.01% of vaccine recipients, which means that it could have missed very rare events occurring in less than 1 out of every 10,000 people. Also, since the first participants were enrolled in July, it would not be able to detect long term effects that did not show up in the first few months after vaccination.

What if I have underlying medical conditions?

The study included patients with a wide range of chronic medical conditions, including a significant proportion of patients with diabetes, pulmonary disease, cancer, obesity and even some patients with heart disease, kidney disease and HIV. This means the vaccine is likely to be safe even in people with common chronic medical conditions.

Importantly, the study excluded pregnant and breastfeeding women. It also excluded immunocompromised patients or those receiving immunosuppressive therapy, including prednisone, as well as those with bleeding disorders. Perhaps most importantly, it excluded patients with a history of severe adverse reaction, such as anaphylaxis, to any prior vaccine. It also excluded patients under 12 years and only tested a small number of patients between 12 and 15. People in these groups do not have good data on which to make a vaccination decision, and if offered the Pfizer/BioNTech vaccine they will need to make an individual decision or wait until more data is collected.

Can we trust the FDA’s decision to approve the vaccine?

Given the severity of the Covid-19 pandemic, with over 3,000 people dying of the disease each day in America, the FDA absolutely accelerated its usual timeline for vaccine approval. It also certainly faced pressure from the White House to approve the Pfizer/BioNTech quickly. However, the FDA based its decision on an independent scientific advisory board of public health, vaccine, and infectious disease experts, who reviewed all the data themselves and overwhelmingly voted to recommend the vaccine for immediate use.

More importantly, the results of the trial were published on December 10th in the prestigious New England Journal of Medicine, after rigorous peer review by independent experts with no relation to the FDA and no relationship to the company. All the information provided above is from the publication in the New England Journal of Medicine, not from the FDA.