We need your help now

Support from readers like you keeps The Journal open.

You are visiting us because we have something you value. Independent, unbiased news that tells the truth. Advertising revenue goes some way to support our mission, but this year it has not been enough.

If you've seen value in our reporting, please contribute what you can, so we can continue to produce accurate and meaningful journalism. For everyone who needs it.


FactCheck: A claim that Covid -19 vaccines don’t stop transmission of the virus is misleading

A now suspended account on Twitter made the claim, but does it have any truth to it?

For Covid factchecks

A POST CLAIMING that Covid -19 vaccines don’t “stop transmission” has gained traction on social media platforms.

A version of the claim originated from a suspended account with the handle @Alex_Zeck on Twitter, before being re-shared on other platforms.

Alec Zeck is a co-founder of Health Freedom for Humanity, a group for the “reclamation and defence of health freedom” according to the group’s website.

His Telegram channel with over 40,000 subscribers regularly features anti-vaccine messages and posts opposing health mandates like vaccine passports.

Zeck has made many claims about the Covid vaccine but is he right on this one? Do vaccines not stop transmission?

The Claim

Zeck claimed on Twitter that Covid-19 vaccines “don’t even stop transmission” of the virus.

His initial Tweet on 23 November read: “I’m honestly asking anyone who’s willing to answer: what’s the ethical, scientific and logic [sic] justification to force the entire world to receive a product made by habitually criminal companies who aren’t liable for injury or death, when the product doesn’t even stop transmission?

Screenshot 2022-02-18 13.07.38 Tweet from @Alec_Zeck reposted on Facebook Facebook Facebook

The tweet went to have a second life at Facebook where it was reposted by 167 groups and public pages, where it garnered 66,000 interactions.  

Zeck once had 85,000 followers on his Instagram page, according to the Guardian, but it has since been removed. 

The Evidence

This is where things get a bit complicated. 

Initial clinical trials of Covid-19 vaccines by Moderna, Pfizer and Johnson & Johnson focused on whether they prevented serious illness and death, and not whether they stopped transmission. 

Early studies indicated that vaccines improved infection rates.

An Israeli study examined Covid-19 cases in healthcare workers from December 2020 to 2021, comparing infections in vaccinated and unvaccinated workers.

It found an 85% adjusted rate reduction in symptomatic Covid cases in workers 15 to 28 days after their first Pfizer dose. 

The study was limited because it had a small sample size of workers from a medical centre; the results therefore might not be the same in the general population, while asymptomatic cases were not examined as a separate category. 

A UK study on household transmission following vaccination from January to February 2021 found that if an index patient (ie the first identified case) was vaccinated, then the likelihood of them passing Covid-19 on to a household contact was 40 to 50 per cent lower than if the index patient was not vaccinated. 

A research team in the Netherlands also examined vaccine effectiveness against transmission in household and close contacts of confirmed cases from February to May 2021.

They found that infection rate of household contacts was 11% for fully vaccinated index cases compared with 31% of unvaccinated cases.

That study calculated that the VET (vaccine effectiveness against transmission) rate was 73% when considering the transmission of the Alpha variant of Covid-19 to unvaccinated household contacts. 

However, when the same researchers performed carried out another study after the Delta variant became dominant, the effectiveness of vaccines against transmission to unvaccinated households contacts dropped to 63%.

The study acknowledged that because the Delta variant is more transmissible than Alpha, a reduced vaccine effectiveness against transmission score was “not unexpected”. 

Ultimately, the study found “results indicate that vaccination confers protection against onward transmission from vaccinated index cases, albeit somewhat less for Delta than for Alpha”.

However, results showed the vaccines’ effectiveness against transmission to household contacts was “stronger” when both the index case and the contact were vaccinated. 

Last year an Imperial College of London study showed that vaccination status had little impact on peak viral load – that is, the highest amount of the SARS-CoV-2 virus found in the throat and nose when a person has Covid-19.

However, fully vaccinated individuals cleared the virus faster, meaning they were infectious for a shorter period of time.

The study contained a mixture of Alpha and Delta cases and showed that unvaccinated household contacts were more likely to be infected than household contacts.

But when it came to transmission, the likelihood of household contacts being infected with Covid-19 was 25 per cent by a vaccinated index case and 23 for an unvaccinated case. 

But does that mean that vaccination status does little to change the rates of transmission? No, according to the study’s author Professor Ajit Lalvani. 

In a previous FactCheck, Professor Lalvani told The Journal that vaccines reduce transmission in two ways.

“First, by reducing the number of people who get infected; second, by reducing the infectiousness of those who do get infected,” he said. 

There is not much research available yet on how Omicron tests vaccine effectiveness against transmission, given the variant was only recorded a few months ago.

A pre-print from a Danish study published in December 2021 found that, compared to the Delta variant, transmission rates for Omicron increased in household contacts increased regardless of vaccination status.

The SAR (ie the likelihood of infection after being exposed) for unvaccinated individuals with Omicron was 1.17 times higher than with Delta, 2.61 times for fully vaccinated people and 3.66 times higher for boosted individuals.

But when it comes to passing on the virus, vaccine status evidently played a part.

The study found that “booster-vaccinated individuals generally had a reduced transmissibility and unvaccinated individuals had a higher transmissibility compared to fully vaccinated adults”.

However, this research is yet to be peer reviewed. 


A claim was made on social media that Covid-19 vaccines don’t reduce transmission.

Research shows vaccines reduce transmission of Covid-19 but they do not stop transmission completely. The Delta and Omicron variants in particular reduced the effectiveness of vaccines against transmission.

However, the results of multiple studies still show that transmission is curtailed in Covid-19 patients who have been vaccinated compared to those who have not. Ultimately, vaccines still help to prevent Covid-19 infection. 

Therefore, the claim that vaccines don’t ‘even’ stop transmission is MISLEADING.

As per our verdict guide, this means the claim either intentionally or unintentionally misleads readers.

TheJournal’s FactCheck is a signatory to the International Fact-Checking Network’s Code of Principles. You can read it here. For information on how FactCheck works, what the verdicts mean, and how you can take part, check out our Reader’s Guide here. You can read about the team of editors and reporters who work on the factchecks here.