For some, the novelty of the COVID-19 vaccinations may be intimidating, and it is normal for concerns about their efficacy to develop. This piece delves into the distinction between effectiveness and efficacy, compares the COVID-19 leading vaccinations to other vaccines, such as the flu shot, and discusses their safety implications.
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The world awaits the effectiveness of Pfizer/COVID-19 BioNTech’s vaccine as it is rolled out across the United Kingdom and the United States.
When comparing the three main vaccine candidates previously reported on, Pfizer/BioNTech claims 95 percent efficacy, Oxford/AstraZeneca claims an average of 70% efficacy, and Moderna claims 94.1 percent efficacy.
However, what does this indicate about their efficacy? And how does it compare to flu, polio, and measles vaccines?
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What is the difference between effectiveness and efficacy?
To begin, it is necessary to distinguish between the terms “effectiveness” and “efficacy.” Despite the fact that news organizations commonly use the terms interchangeably, effectiveness refers to a vaccine’s performance under ideal laboratory settings, such as those found in clinical trials. By contrast, effectiveness relates to how something operates in practice.
In other words, a 90% effectiveness rate in a clinical study indicates that the group receiving the vaccination had 90% fewer incidences of illness than the placebo group.
However, clinical trial participants are usually healthier and younger than the general population, and they do not have any underlying problems. Additionally, researchers exclude some populations from these studies, such as youngsters and pregnant women.
Thus, while vaccination may prevent illness in a clinical trial, its efficacy may diminish when provided to a larger population.
That is not, however, a negative thing.
Efficacy of flu shots
Vaccines do not have to be very effective in order to save thousands of deaths and millions of illness cases.
According to the Centers for Disease Control and Prevention, the widely used flu vaccine has a 40–60 percent efficacy rate (CDC).
However, it averted about “4.4 million influenza infections, 2.3 million influenza-related medical visits, 58,000 influenza-related hospitalizations, and 3,500 influenza-related fatalities” between 2018 and 2019.
Additionally, it is worth mentioning that the flu vaccine’s efficacy changes seasonally, depending on the type of flu virus prevalent that year. Calculating the exact rate of efficacy can be difficult.
Finally, it’s worth noting that increasing the number of doses can also increase the efficacy of certain vaccinations. Two doses of the flu vaccination instead of one can provide an additional layer of protection, although this advantage is restricted to a few select individuals, such as children and organ transplant recipients.
The booster dosage appears to be ineffective in persons over the age of 65 or those with a weakened immune system.
By contrast, as we will see below, vaccinations against polio and measles require a larger number of doses to attain maximum efficacy.
Effectiveness of the polio vaccination
Polio vaccines can be up to 100 percent effective. The CDC states that two doses of inactivated polio vaccine (IPV) are 90 percent or more effective against polio; three doses are 99 percent to 100 percent effective.
However, experts prescribe four doses of IPV. The CDC recommends that children receive one dose of the vaccine at the age of two months, another dose at four months, a third dose between the ages of six and eighteen months, and a final fourth dose between the ages of four and six years.
When these four dosages are combined, they achieve efficacy of 99–100 percent.
The IPV vaccination protects against poliomyelitis, a condition caused by the poliovirus. The poliovirus can induce infection in the brain and spinal cord, resulting in paralysis.
Effectiveness of the measles vaccination
When taken in two doses, the MMR vaccination, which protects against measles, mumps, and rubella, can be up to 97 percent effective at preventing measles.
According to the CDC, one dosage is roughly 93% effective.
The CDC recommends providing the first dosage between the ages of “12 and 15 months” and the second dose between the ages of “4 and 6 years.”
How do the adverse consequences stack up?
When it comes to new vaccinations, everyone’s mind naturally turns to safety.
The phrase “how safe is this vaccine?” may be translated as “what is the risk of having adverse reactions to this vaccine?” And, in addressing this question, it’s critical to remember that no medicine — not even the most often prescribed painkiller — is completely free of adverse effects.
Scientists have classified the expected adverse effects of the BioNTech vaccine — presently the only one approved for use in the United Kingdom and the United States — as “extremely frequent,” “common,” and “uncommon.”
The following are extremely frequent adverse effects, which may affect more than 1 in 10 people:
- pain at the injection site
- tiredness
- headache
- muscle pain
- chills
- joint pain
- fever
The most frequent adverse effects, which may affect up to one in ten persons, are as follows:
- injection site swelling
- redness at the injection site
- nausea
Uncommon adverse effects include enlarged lymph nodes and general malaise, which may affect up to 1 in 100 persons.
By comparison, the CDC lists the following as frequent flu shot adverse effects:
- soreness and redness, swelling, or both, from the shot
- headache
- fever
- nausea
- muscle aches
They note that the flu vaccine, like any other injection, may occasionally induce fainting. The CDC recommends that everyone receive the flu vaccination, with the exception of children less than six months of age and individuals who have severe allergies to the flu vaccine or any of its ingredients.
Certain studies have discovered a small risk of Guillain-Barré syndrome following flu vaccination, whereas others have discovered no such risk. For those who did discover such a possibility, the risk was estimated to be 1–2 in 1,000,000 persons.
The CDC lists the following as common adverse effects of MMR:
- sore arm from the shot
- fever
- mild rash
- temporary pain and stiffness in the joints
Occasionally, the vaccination may cause febrile convulsions, cheek or neck edema, or a transient low platelet count in the blood. None of them, however, are life-threatening or have long-term consequences.
In the case of polio, the CDC notes that “a painful area with redness, swelling, or discomfort around the injection site may occur following a polio vaccine.” Additionally, “like with any medication, there is a very small possibility that a vaccination could cause a severe allergic response, other serious damage, or death.”
COVID-19 vaccination and adverse events
Since the BioNTech vaccine was introduced in the United Kingdom, two patients — both of whom had a history of severe allergies — experienced adverse responses.
This prompted authorities to warn that those with a history of severe allergic responses refrain from receiving the COVID-19 vaccination.
While it is better to err on the side of caution during the early phases of a vaccine’s rollout, it is important noting that all vaccinations, including those for polio, influenza, and measles, have a risk of provoking severe adverse responses.
This risk is around one in 900,000 persons.
The safety results for the COVID-19 vaccine and vaccine candidates are based on tens of thousands of patients who received the vaccination in the Pfizer/BioNTech, Moderna, and Oxford/AstraZeneca trials.
Thus, the safety data obtained from this sample size is sufficient for regulators to determine if a vaccination is safe enough to license. However, it may not be sufficient to detect uncommon occurrences, such as those affecting one in 100,000 persons.
As Dr. Charlie Weller, Head of Vaccines at the Wellcome Trust in London, UK, notes, “far more data would be required to assess if there is any link between the vaccination and these [allergic] responses.” Following that, guidance would be provided to individuals who may be at risk.”
“With the vaccination distribution only getting started, there are still several unresolved issues. Continuous monitoring will assist us in identifying any trends of adverse occurrences. As is customary with any vaccination, thorough and ongoing monitoring of safety and effectiveness data during administration will be critical.”
— Charlie Weller, M.D.
“This does not indicate that the general public should be fearful of obtaining the vaccination,” Prof. Stephen Evans, Professor of Pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, adds.