Sarah Bennett
Vaccines are one of the greatest inventions in the history of medicine, saving hundreds of millions of lives. However, no vaccine is 100% effective. For instance, the COVID-19 vaccines developed by Pfizer/BioNTech and Moderna are about 95% effective at preventing symptomatic illness. The flu vaccine is typically 30-70% effective, and the MMR vaccine is about 85% effective after two doses. While no vaccine offers total protection, they are still extremely effective and induce immunity that surpasses natural immunity from exposure to a virus.
| Characteristics | Values |
|---|---|
| Are there any 100% effective vaccines? | No, no vaccine offers 100% protection. |
| Example of vaccines that are not 100% effective | Influenza vaccine, MMR vaccine, COVID-19 vaccines |
| Effectiveness of the Influenza vaccine | Typically in the 30-70% range |
| MMR vaccine effectiveness | Approximately 85% effective after two doses |
| COVID-19 vaccine effectiveness | Pfizer/BioNTech, Moderna, and Johnson & Johnson vaccines are about 95% effective at preventing symptomatic illness |
| Effectiveness of vaccines in general | Vaccines are extremely effective, and they induce immunity that beats natural immunity |
| Example of diseases that are becoming rare due to vaccinations | Polio and diphtheria |
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What You'll Learn
No vaccine is 100% effective
Vaccines have helped in the fight against several deadly diseases. For example, the widespread use of the mumps vaccine in the U.S. starting in 1967 led to a 99% decrease in reported cases in the following decades. Similarly, polio and diphtheria are becoming rare in the U.S. thanks to vaccinations.
However, the recent COVID-19 pandemic has brought the issue of vaccine efficacy to the forefront. While the Pfizer/BioNTech, Moderna, and Johnson & Johnson vaccines were found to be 100% effective in preventing severe disease and hospitalizations in clinical trials, they are not 100% effective in the real world. In fact, no vaccine is 100% effective in preventing infection or transmission.
The flu vaccine, for instance, typically has an effectiveness range of 30-70% due to viral mutations. Even the highly effective MMR (measles, mumps, and rubella) vaccine is only approximately 85% effective after two doses. Despite not being perfect, vaccines still induce immunity that surpasses natural immunity from exposure to a virus.
The key to building confidence in vaccines lies in transparency about their effectiveness, characteristics of individuals for whom they may not work as well, and any rare adverse effects.
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COVID-19 vaccines prevent hospitalisation and death
No vaccine is 100% effective, and they do not totally stop infection or transmission. However, COVID-19 vaccines have been proven to prevent hospitalisation and death.
The COVID-19 vaccines developed by Pfizer/BioNTech and Moderna are about 95% effective at preventing symptomatic illness. This means that vaccinated people in the clinical trials had a 95% lower risk of getting COVID-19 compared to the unvaccinated control group participants.
The Pfizer/BioNTech, Moderna, and Johnson & Johnson clinical trials all found that their vaccines were 100% effective in preventing severe disease six to seven weeks after trial participants had received a first/single dose. No vaccinated people in any of the trials were hospitalized or died of COVID-19 after the vaccines had fully taken effect.
Data has shown that COVID-19 vaccines provide protection against severe illness, even in breakthrough cases. Vaccinated people who still get COVID-19 are less likely to develop serious illness than those who are unvaccinated. Their symptoms tend to be less severe, meaning they are much less likely to be hospitalized or die than people who are not vaccinated.
A 2023 study undertaken by the Indian Council of Medical Research-National Institute of Epidemiology (ICMR-NIE) found that COVID-19 vaccination prevented sudden deaths and did not cause them. The study was conducted in 50 hospitals across India, including about 800 patients of sudden death and about 3,000 healthy controls.
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The flu vaccine is 30-70% effective
No vaccine is 100% effective, and they don't need to be 100% effective to be useful. Vaccines induce immunity that is more effective than natural immunity from exposure to a virus.
The flu vaccine is typically 30-70% effective. Effectiveness varies depending on the season, the age of the patient, antigenic match or mismatch, and the manufacturing process. For example, a study in China during the 2011-2012 influenza season, which was characterised by a mismatch of H3N2 and B viruses, estimated a vaccine effectiveness of 67%. In contrast, a study in the Republic of Korea during the 2017-2018 season showed a vaccine effectiveness of 59.3%.
The flu vaccine's effectiveness is lower than that of some other vaccines, such as the smallpox vaccine, the yellow fever vaccine, and the measles, mumps and rubella (MMR) vaccine. The flu vaccine's effectiveness varies from year to year because viral mutations occur every year.
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MMR vaccine is 85% effective
No vaccine is 100% effective, and they do not necessarily stop infection or transmission entirely. However, vaccines are one of the greatest inventions, saving hundreds of millions of lives.
The MMR vaccine, which protects against measles, mumps, and rubella, is a highly effective vaccine. It has been in use for over 60 years, and in that time, we rarely see the severe effects of the illnesses it protects against. The MMR vaccine is estimated to be 85% to 95% effective after the first dose, with the second dose increasing efficacy to 97% for measles and rubella and 86% for mumps. This small risk of infection is why healthcare providers recommend the MMR vaccine for anyone who can safely get it.
Measles, mumps, and rubella are highly contagious viral infections that can cause serious, life-threatening health conditions, including pneumonia, brain inflammation, blindness, hearing loss, and even death. Before the MMR vaccine was introduced, measles resulted in 2.6 million deaths per year. As of 2012, this number had decreased to 122,000 deaths per year, mostly in low-income countries. Between 2000 and 2018, measles deaths decreased by 73% due to vaccination.
While the MMR vaccine is effective at protecting against all three illnesses, some people may lose immunity to mumps over time and may need an additional dose during a mumps outbreak. Additionally, the MMR vaccine is not recommended during pregnancy due to the presence of live viruses, but it may be given during breastfeeding.
The MMR vaccine has been the subject of controversy, with some media reports linking it to autism. However, rigorous scientific studies and reviews have provided considerable evidence to refute these claims. The decline in vaccination rates due to these reports has had real-world consequences, with measles cases increasing significantly in the UK after the publication of Wakefield's article in 1998.
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COVID-19 vaccines reduce transmission
No vaccine is 100% effective, and they do not necessarily stop infection or transmission. However, COVID-19 vaccines have been shown to reduce the chance of infection and provide protection from severe illness, even in breakthrough cases.
According to a pre-print analysis in The Lancet medical journal, the AstraZeneca-Oxford vaccine reduced the rate of positive PCR tests by half when two doses were administered. A single dose resulted in a 67% reduction. A Cambridge University study suggests that one dose of the Pfizer-BioNTech vaccine can reduce fourfold the number of asymptomatic COVID-19 infections.
A CDC study of COVID-19 transmission in households with children found that the virus was transmitted from people of all ages, both with and without symptoms. However, vaccinated people were much less likely to develop serious illness and were less likely to be hospitalized or die. The study did not find that vaccination reduced transmission within households.
Another study found an 85% reduction in symptomatic COVID-19 infections within 15 to 28 days of receiving a first dose of the Pfizer vaccine, with an overall reduction in infections, including asymptomatic cases, of 75%. Gerald Evans, an infectious disease specialist at Queen's University, said, "If you never get infected, then it's also possible that you won't transmit it to other people."
While the COVID-19 vaccines may not entirely prevent transmission, they play a crucial role in curbing the spread and reducing the severity of the disease.
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Frequently asked questions
No vaccine provides 100% protection against a disease, but they don't need to in order to be effective. Vaccines induce immunity that is far superior to natural immunity resulting from exposure to a virus.
No, the COVID-19 vaccines are not 100% effective. The Pfizer/BioNTech and Moderna vaccines are about 95% effective at preventing symptomatic illness. However, they are 100% effective in preventing hospitalizations and deaths.
Yes, the smallpox vaccine, the yellow fever vaccine, and the measles, mumps, and rubella (MMR) vaccine are all highly effective. The MMR vaccine is approximately 85% effective after two doses.
No medical intervention is 100% effective. In addition, efficacy is complex and can mean a number of different things, making it difficult to compare numbers presented in the press for different vaccines.
