COVID-19 vaccines are highly effective but don’t prevent the disease completely; unvaccinated people place themselves and others at risk as a reservoir for virus spread

'Remember to get vaccinated or a vaccinated person might get sick from the virus they got vaccinated against because you're not vaccinated'
Misleading: COVID-19 vaccines are very effective at preventing illness. However, no vaccine is 100% effective, and a small proportion of fully vaccinated people can still get sick if they become infected.
Lack of context: Unvaccinated people are much more likely to become infected, offering more opportunity for the virus to spread and reducing the population's immunity. A higher number of infections increase the chances for the virus to mutate, facilitating the emergence of new variants. This poses a greater risk of transmission to others, including vaccinated people.
The three COVID-19 vaccines authorized for emergency use by the Food and Drug Administration prevent COVID-19 hospitalization by at least 89% and are an effective way to protect oneself and others against the disease. However, they don’t completely prevent it. Unvaccinated people facilitate the spread of the virus, increasing the risk of exposure, infection, and severe illness among all the community members, including those who are fully vaccinated.

FULL CLAIM: 'Remember to get vaccinated or a vaccinated person might get sick from the virus they got vaccinated against because you're not vaccinated'


In early July 2021, this meme claiming that “a vaccinated person might get sick from the virus they got vaccinated against because you’re not vaccinated” went viral on social media platforms. The meme received more than 65,000 interactions on Facebook, Instagram, and Twitter, according to the social media analytics tool CrowdTangle.

This meme is yet another addition to a line of social media posts questioning the effectiveness of COVID-19 vaccines by implying that the vaccines aren’t effective, since vaccinated people can still be infected by unvaccinated people.

As we discuss below, this line of reasoning fails to account for two important considerations. The first one is that no vaccine is 100% effective, so a small proportion of vaccinated individuals might still get sick. The second one is that unvaccinated individuals are more likely to get infected, favoring the spread of the virus within the whole community and the emergence of new variants.

COVID-19 vaccines are highly effective, but a small percentage of people who are fully vaccinated may still get COVID-19 if they are exposed to the virus

The three COVID-19 vaccines authorized by the U.S. Food and Drug Administration (FDA) are highly effective at preventing severe disease. According to the U.S. Centers for Disease Control and Prevention (CDC), they all reduced the number of COVID-19 patients needing hospitalization by at least 89%. The Pfizer-BioNTech and Moderna mRNA COVID-19 vaccines showed 95% and 94% efficacy, respectively, at preventing symptomatic COVID-19[1,2]. A single dose of the Johnson & Johnson COVID-19 vaccine demonstrated 85% efficacy at preventing critical illness[3].

Evidence from several studies also confirmed the effectiveness of FDA-authorized COVID-19 vaccines in real-world conditions. One study from Israel showed that two doses of the Pfizer-BioNTech mRNA COVID-19 were more than 96% effective at preventing hospitalization and death. The vaccine was also 91% effective at preventing infection[4]. Interim results from the U.S. Centers for Disease Control and Prevention (CDC) also showed that both mRNA COVID-19 vaccines were more than 91% effective at preventing infection among health care workers and other frontline workers[5].

However, no vaccine is 100% effective and the COVID-19 vaccines are no exception. This means that a small proportion of people who are fully vaccinated will still get infected. Such cases are known as vaccine breakthrough infections. Breakthrough cases are expected and don’t render COVID-19 vaccines useless, as the post implied. Although a few cases might end up in hospitalization or death, breakthrough cases are rare and tend to be milder than in unvaccinated individuals[5,6].

As of 6 July 2021, the CDC received 4,909 reports of hospitalizations and 988 deaths due to breakthrough infections among the more than 157 million people who have been fully vaccinated against COVID-19. As the CDC website explains, about one-third of these cases were asymptomatic, and their hospitalization or death was unrelated to COVID-19.

Unvaccinated people are more likely to contract the disease themselves, favoring the spread of the virus and the risk of outbreaks

As Health Feedback explained earlier in this review, the vast majority of COVID-19 deaths and hospitalizations in the U.S. now occur in unvaccinated people. The director of the CDC, Rochelle Walensky, explained in a 1 July 2021 White House briefing that over 99% of the COVID-19 deaths that occurred in the U.S. between January and June 2021 were among unvaccinated people, according to preliminary CDC data.

Viruses are obligate parasites, which means that they can only survive by infecting new people. When most individuals within a community are protected against the disease, the virus has less opportunity to spread. Therefore, vaccination indirectly reduces the risk of infection among all the individuals within that community, even unvaccinated people. This effect is known as population immunity or herd immunity.

More infections within a population mean that more people will get exposed to the virus, including those who are vaccinated. This increases the likelihood of disease outbreaks. Such was the case in the 1989 measles outbreak in the U.S., which originated in areas with low vaccination coverage and caused more than 55,000 cases and 123 deaths. Even though the proportion of vaccine breakthrough cases is small, a higher exposure translates into more vaccinated people who will become sick.

Furthermore, certain groups of people are particularly at risk because they rely solely on herd immunity to protect them. These groups include people who can’t receive the vaccine, like children under the age of 12 or people who are allergic to some vaccine component, and people who are unable to mount an adequate immune response to vaccination. For example, vaccines tend to be less effective in immunocompromised people[7].

A higher number of infections increases the chances for the virus to mutate

Each time the virus replicates during the infection process, it can produce mutations or changes in its genetic sequence. The more infections the virus causes, the more times it replicates, increasing the likelihood of generating new mutations. Many of these changes don’t affect the viral function or may even weaken it. However, some of them may increase the ability of the virus to infect cells or cause severe disease, resulting in a more dangerous variant.

Although variants of the virus can also emerge in vaccinated populations, clusters of unvaccinated individuals are much more likely breeding grounds for new variants to arise. The reason is that mutations are more likely to occur during longer infections and when more people are infected[8].

Real-life data suggests that FDA-authorized COVID-19 vaccines are effective against currently circulating variants of concern. One study from Qatar found that the Pfizer-BioNTech COVID-19 vaccine was more than 97% effective against severe disease or death from the Alpha variant, first detected in the U.K, and the Beta variant, first identified in South Africa[9].

First identified in India, the Delta variant has become dominant in many countries, including the U.S. A preliminary report from the U.K.’s Public Health England in 3,975 essential workers found that two doses of the Pfizer-BioNTech COVID-19 vaccine are still effective against the Delta variant, preventing disease by 88% and hospitalization by 96%. In a 1 July 2021 news release, Johnson & Johnson reported that their COVID-19 vaccine was also effective against the Delta variant eight months after vaccination, and two doses generated an immune response in 95% of the individuals[10,11].

Because clusters of unvaccinated individuals make it easier for the virus to spread within a community, they also make it more likely for new variants to emerge. If some of these variants escape the immune response elicited by COVID-19 vaccines, they would spread easier and faster among the population, causing a resurgence of COVID-19 cases.


Although COVID-19 vaccines are highly effective against severe disease, they can’t prevent it completely. This imperfection doesn’t render vaccines useless, as the meme implied, as the vaccines greatly reduce the number of infections, hospitalizations, and deaths arising from COVID-19. The presence of unvaccinated individuals within a community makes it more likely for transmission to occur and favours the emergence of new variants, thereby posing a risk for themselves and vaccinated individuals.



Published on: 15 Jul 2021 | Editor:

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