Are 75% of people infected with Delta Covid strain already vaccinated? No. Facebook post mangles CDC study

“Kan julle die teendeel bewys? CDC in VSA het bevind dat 75 persent van mense wat positief toets met Delta variant is reeds ten volle geent,” reads a message posted on Facebook in South Africa on 26 August 2021. “Alie [al die] middels is ter sprake. Weet jy dit minister?”

This is Afrikaans for: “Can you prove the opposite? CDC in USA found that 75% of people who test positive with Delta variant have already been fully vaccinated. That includes all the vaccines. Do you know that minister?”

The message seems to be a screenshot of a discussion on social media. “Minister” probably refers to a minister heading a South African government department.

The CDC is the Centers for Disease Control, the US government agency leading that country’s response to the Covid-19 pandemic.

The highly contagious Delta variant of the Sars-Cov-2 coronavirus that causes Covid-19 was first identified in India in December 2020. It is now the dominant strain of the virus in many countries, including South Africa, Kenya and Nigeria, and the US.

“Breakthrough” infections happen when a person gets a disease they have been vaccinated against. But has the CDC found that two thirds of people in the USA who test positive for the Delta coronavirus strain are already fully vaccinated against Covid-19?

Summer festivities in Provincetown

After an extensive online search, Africa Check found that the only information that remotely matched the claim was a CDC Morbidity and Mortality Weekly Report released on 30 July. This details a Covid outbreak of just 469 people that started in a small town in Massachusetts, a state of about 7 million people in the northeast corner of the US.

A CNBC news report on it is headlined: “CDC study shows 74% of people infected in Massachusetts Covid outbreak were fully vaccinated.”

The outbreak, the CDC says, began during “multiple summer events and large public gatherings” in a Barnstable county town. Media reports identify the town as Provincetown, a popular tourist destination on the northern tip of the Cape Cod peninsula on the US Atlantic coast.

“Persons with Covid-19 reported attending densely packed indoor and outdoor events at venues that included bars, restaurants, guest houses, and rental homes,” the CDC says in its report.

The 469 people who made up the outbreak were Massachusetts residents who lived in or had travelled to Provincetown in the two weeks from 3 to 17 July. Of the 469 people infected, 346 were fully vaccinated. That’s 74% of the total cases.

The vaccinated people had received either both doses of the Pfizer-BioNTech or Moderna vaccines, or the single Johnson & Johnson jab. These are the Covid vaccines currently authorised for use in the USA, but not all the Covid vaccines available, as the message claims. The New York Times coronavirus vaccine tracker identifies 13 vaccines in early or limited use across the world, and eight approved for full use.

CDC study recommends masks

From a sample of 133 patients, it seems most of the people infected in the outbreak had the Delta variant. Covid-19 symptoms appeared in 274 of the vaccinated people: most commonly cough, headache, sore throat, muscle pain and fever.

Five of the 469 people in the outbreak were hospitalised. Four were fully vaccinated. Three of the five – one unvaccinated, two vaccinated – had underlying medical conditions.

No deaths were reported.

The CDC study got wide media coverage in the US, mainly because it prompted the agency to reverse its advice on wearing masks.

The study’s summary reads: “Jurisdictions might consider expanded prevention strategies, including universal masking in indoor public settings, particularly for large public gatherings that include travellers from many areas with differing levels of Sars-Cov-2 transmission.”

Vaccines prevent sickness, hospitalisation – and death

The US had an estimated population of 328 million people in 2019. A small study of a Covid outbreak from a single town, totalling 469 patients, doesn’t represent the entire country.

And no vaccine, against any disease, is perfect. Covid vaccines do prevent people from getting the disease. More than this, they prevent serious Covid sickness, prevent people from having to go to hospital, and prevent them from dying.

Gavi, a Switzerland-based organisation that works to increase vaccination rates in less developed countries, explains:

With large numbers of people being vaccinated, and as almost all Covid-19 restrictions are lifted in some countries, it is inevitable that a small proportion of fully vaccinated individuals will become infected. An even smaller proportion will become seriously ill and die. What's important is that the risk of a serious outcome is vastly lower for those who have been fully vaccinated against Covid-19, compared to those who have received no vaccine doses.

In early August, CDC data reported in the media – including the conservative Fox News – showed that more than 164 million people in the USA had been fully vaccinated against Covid-19.

Of those, just 0.0038% of the vaccinated population – 6,239 people – had been admitted to hospital with Covid. And just 0.00077% of the vaccinated – 1,263 people – had died from the disease.

That means just one person out of about 26,000 vaccinated people had been hospitalised, and one out of 130,000 had died.

On 23 August, the CDC published a report that began with a blunt statement. “The bottom line: Covid-19 vaccines protect people against severe illness, including disease caused by Delta and other variants circulating in the US.”

The message uses a single study of 469 people to suggest that all people in the USA – a country of hundreds of millions of people – who test positive for the Delta Covid variant have been vaccinated. It is untrue, and deliberately misleading.