COVID-19 Vaccine Comparisons: Efficacy

COVID-19 Vaccine Comparisons: Efficacy

As people worldwide start getting vaccinated, it is important to understand that the differences in vaccine statistics, especially efficacy, do not completely determine their effectiveness or their safety. Although sometimes inaccurate, efficacy helps people quantify how much safer people who take the vaccine are compared to the unvaccinated people. Efficacy is usually presented as a percentage since it represents the percentage of risk reduction of the disease in vaccinated people compared to unvaccinated people. A 95% efficacy does not mean that 5% of vaccinated people will get sick. It means that a vaccinated person is 95% less likely to get infected and get sick. Usually, a vaccine’s efficacy is determined through clinical trials, where the vaccine is tested on large amounts of people.

The four main COVID-19 vaccine producers (Pfizer, Moderna, Johnson&Johnson, AstraZeneca) all have different efficacy rates. The vaccines from Pfizer and Moderna have extremely high efficacy: 95% and 94% respectively. However, Johnson&Johnson and AstraZeneca only have an efficacy of 66% and 82% respectively. If people only look at the percentages at face value, it seems as if the Johnson&Johnson and AstraZeneca vaccines are much less effective than the Pfizer and Moderna vaccines.

Knowing how efficacy is produced is important in understanding that the COVID-19 vaccines are similar in quality, effectiveness, and safeness, regardless of their efficacy. Efficacy is calculated using the results of large-scale clinical tests, which sometimes require tens of thousands of people. The people in the trials are broken into two groups: half of which get the vaccine, and half of which get a placebo. The scientists then monitor the health of the subjects, recording the number of people who get infected with the disease in each category. If an equal amount of people get infected in each category, it means that people are equally as likely to get sick with the vaccine as without it, thus suggesting that the vaccine has 0% efficacy. If no one in the vaccinated category got sick, but some people in the placebo category got sick, it would suggest that the vaccine has 100% efficacy. For example, in the Pfizer category, 5% of the people who got sick were in the vaccinated group and 95% of the people who got sick were in the placebo group. Thus, the Pfizer vaccine has a 95% efficacy.

A vaccine’s efficacy seems like a rather reasonable and accurate measure of vaccine effectiveness on the surface. However, each vaccine’s testing could have been done in extremely different circumstances. Both the Pfizer and Moderna vaccines were conducted in the United States, during a time period with relatively few cases and no variants. However, Johnson&Johnson conducted their trials not only in the United States but also in other countries, such as South Africa and Brazil. Since the other countries had more frequent cases and more infectious variants compared to the United States, the efficacy of the Johnson&Johnson vaccine was lower. Experts theorize that if all the vaccines were conducted in similar conditions, the efficacy of the vaccines would have been much more similar.

One crucial fact about vaccines, especially COVID-19 vaccines, is that they are not always meant to make a person completely immune to a certain disease. They just need to prevent the person from developing serious symptoms or dying. In the absolute best circumstances, vaccines give you complete protection against the virus. Realistically, COVID-19 vaccines most likely only have the ability to make an infection feel like a cold, which is much better than the alternatives: hospitalization or death. Regardless of the efficacy rates, all vaccines can prevent COVID-19 from exhibiting more severe symptoms in your body.

As Dr. John Torres says, “[The] best vaccine is the one that’s available to you first”. Even though the efficacy or other statistics are different between the vaccines, they all do one thing perfectly: prevent you from dying.


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