Which COVID-19 vaccine has the lowest rate of breakthrough infections?

The majority of COVID-19 cases in America are currently occurring in unvaccinated individuals. However, a small number of cases occur in people who have been vaccinated. These cases are called breakthrough infections. Is there a difference between the number of breakthrough infections and which vaccine someone received?We don't know the exact answer, but we do have some clues in the data. Although the Johnson & Johnson vaccine seems to have higher rates than Moderna and Pfizer vaccines for breakthrough infections, this was expected based upon clinical trials. Although some early indications suggest that the Moderna vaccine has a lower rate of breakthrough infection than the Pfizer vaccines, this early data is only based on two million individuals and may not reflect the entire country.Related: 5 myths that are dangerous about vaccinesSince no vaccine is perfect, breakthrough infections are expected at the beginning of vaccine rollout. Clinical trials showed that about 0.04% of those who received the Pfizer vaccine were infected by SARS-CoV-2. This compares to 0.07% for Moderna and 0.59% for Johnson & Johnson.Scientists now have the ability to monitor how many new infections are discovered in real-world settings, after vaccines have been approved. Current data indicates that most people will experience mild symptoms if they become ill. A small number may develop severe illness, need hospitalization, or even die from the breakthrough.However, the recent rise in the highly transmissible delta variant could increase the risk of developing breakthrough infections. A recent Centers for Disease Control and Prevention study published as a Morbidity and Death Weekly Report (MMWR), Aug. 6, found that the prevalence of the delta variant in Mesa County, Colorado, between May and June, was higher than other Colorado counties.The reporting of breakthrough infections is now largely up to the states. Of the 25 states that do report them, many don't provide data on the number and severity of each brand. Live Science discovered this through a search on state health department websites.This information is made public by Washington, D.C., and Oklahoma. The DC Health website says that these data can provide "early indicators" about how vaccines are working and new variants as they emerge. Despite this, the data is limited in that each vaccine was administered to different people, and it's difficult to interpret the data due to the time of administration.Related: Coronavirus variants - Here's how SARS-CoV-2 mutants compareAccording to DC Health data, more than 299,000 D.C. residents were fully vaccinated as of August 1. Nearly 151,000 people received the two-dose Pfizer vaccine; 124,700 received the two dose Moderna vaccine; and 24,000 received the Johnson & Johnson one-dose vaccine.The highest number of breakthroughs in this population was among those who received the Johnson & Johnson shot. This is 77 people or 0.32% out of approximately 24,000 recipients. Pfizer recipients had the second highest rate, with 308 (or 0.2%) of them testing positive for the virus. The breakthrough infection was finally caught by 161, or 0.13 percent, Moderna recipients.These cases include mild, moderate, severe, and asymptomatic cases. People with mild or asymptomatic infections might not be tested. This would mean that their cases may be overlooked, which could lead to an undercount in breakthroughs.Related: 20 of The Worst Pandemics and Epidemics in HistorySimilar results were reported by Oklahoma.According to the Oklahoma State Department of Health, more than 1.5 million Oklahomans were fully vaccinated as of August 2. About 817,000 people had received Pfizer shots. 674,000 received Moderna, and 102,000 received Johnson & Johnson. The highest number of breakthrough cases was again seen in Johnson & Johnson recipients. 215, or 0.21% of them, tested positive for the virus. 1,468 Pfizer recipients (0.17%) were among the recipients who caught the virus. 831 Moderna recipients (0.12%) also tested positive.The snapshots taken in Oklahoma and D.C. may not give a complete picture of breakthrough cases. It is also unclear whether the patterns observed are representative of the entire country. We need more data to compare vaccine brands, especially the delta variant, said Robert Darnell, a New York physician scientist at The Rockefeller University.Reuters reported that preliminary research suggests Moderna's vaccine is more effective against the delta variant of the disease than Pfizer's. This could explain differences in breakthrough rates. A study published Aug. 8 on bioRxiv included more than 50,000 patients from the Mayo Clinic Health System. It found that Moderna's real-world effectiveness dropped from 86% to 76% in January and July when delta became popular. Pfizer's effectiveness dropped from 76% to 42% during the same time frame.The results of this study have not yet been peer-reviewed, so they need to be confirmed.Original publication on Live Science