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Reports are trickling in of people who contracted COVID-19 even though they were vaccinated, like these four people in Oregon and these 12 in Hawaii. But these are just a few cases out of millions vaccinated. New research confirms that the vaccines are overwhelmingly effective in real-world use, and that breakthrough cases like these are rare.
According to the phase 3 studies that were required before the vaccines could be approved, the Moderna vaccine worked out to be 94% effective against symptomatic infection and the Pfizer vaccine 95% effective. These numbers refer to vaccine efficacy, a number calculated from lab trials. If the number of cases in a group of vaccinated people is 5% as many as in the control group, that vaccine has an efficacy of 95%. It’s an important number to calculate in a trial, but it’s not the same as real-world effectiveness.
In the same way, the Johnson & Johnson vaccine was calculated as 66% effective, although the vaccine trial was tested in a setting with more of the new variants in circulation, so this number can’t be directly compared to the other two. Experts have said all three vaccines are effective and there’s no strong reason to turn down any one vaccine in preference to another.
What about real-world effectiveness?
A new study out today provides more information on effectiveness in real-world situations. Almost 4,000 people who received the Pfizer or Moderna vaccine in December were followed for three months; they swabbed their noses regularly and sent samples to the CDC to be tested for the coronavirus, whether they felt sick or not.
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The results were excellent: the people in the study were 90% protected from infection once they were fully vaccinated (14 days after their second dose) and 80% protected during the time period that started 14 days after their first dose.
The volunteers in the study were healthcare workers and other essential workers, mainly between ages 18-49, mostly white, and included more women than men.
While the phase 3 trials only tested participants if they had symptoms of COVID, this study tested everybody, so we have a new piece of information: the vaccines are effective against infection, not just symptomatic infection. Until recently, we weren’t sure if the vaccines stopped people from getting the virus or just made them less likely to develop symptoms. This study is among the first to show that the vaccine prevents asymptomatic infections, too.
Breakthrough infections are rare
But there were still breakthrough infections. Among 994 people who were not vaccinated, 161 developed infections. Compared to that, the vaccine was very effective, but not perfect. There were eight infections in people who received only one dose of the vaccine, and only three among people who got both doses.
When you see news reports of breakthrough infections, it’s important to put them in context. If there are so few of these that every handful of cases warrants a news report—among the 51 million people who have been fully vaccinated—that itself is a sign that the vaccines are working pretty darn well.
It’s also important to note that breakthrough infections may turn out to not be as serious as those infections in people who have not received the vaccine. All three vaccines were shown in their trials to be extremely effective against death and severe disease.
Whether breakthrough infections are milder or not is one of many open questions about breakthrough infections that researchers are still trying to answer. Others include whether breakthrough infections in the study may have been caused by newer variants of the coronavirus, or whether the people with breakthrough infections had anything else in common (such as pre-existing medical conditions).
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