A pharmacy technician takes delivery of the first batch of Covid-19 vaccinations at Croydon University Hospital in south London © Gareth Fuller/Pool/AFP/Getty

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The writer is a science commentator

In 2009, Natalie Morton, a British teenager, collapsed and died after receiving the human papillomavirus vaccine at school. The tragedy was splashed across newspapers and raised fears over a vaccine that had been given to more than 1m girls.

Natalie’s death turned out to be a terrible coincidence. A postmortem revealed the schoolgirl had an undiagnosed large malignant tumour in her heart and lungs that could have killed her at any time. Her death, experts concluded, was unrelated to the vaccine.

The mass rollout of the Covid-19 vaccines will surely be beset by many such coincidences — with considerable potential for unnerving the public. The jabs are being prioritised for use in the oldest and most vulnerable, among whom the risk of suddenly dropping dead or falling ill is higher than for teenagers. That has the potential to feed anti-vaccination sentiment. Public confidence in the rollouts, which begin on Tuesday in the UK and in mid-December in the US, may rest on convincing people that many of the unfortunate things that happen by chance soon after vaccination would have occurred without the jab.

One US researcher involved in drawing up the US Centers for Disease Control’s priority lists for vaccination recently voted against elderly care home residents being immunised first, partly because their higher rates of death and ill-health might be mistakenly ascribed to Covid-19 vaccines. Helen Keipp Talbot, an associate professor at Vanderbilt University, also dissented because clinical trials have not proven that the formulations work in this specific group. The over-65s fit enough to be recruited to trials, she told Stat news service, are not representative of the often very frail residents in nursing homes.

Other researchers are similarly concerned that the ever-present background noise of medical misfortune will be misread as vaccine side-effects. Bob Wachter, who heads the department of medicine at the University of California, San Francisco, crunched the numbers on the usual run of maladies and mortality expected in a group of 10m Americans over the course of two months: he calculates around 4,000 will have a heart attack; another 4,000 will have a stroke; about 9,500 will be newly diagnosed with cancer; 60 will be diagnosed with multiple sclerosis; and 14,000 will die of various causes.

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Illnesses that usually go unremarked upon may acquire sinister significance when they appear after vaccination, despite being unconnected. Derek Lowe, who writes a blog for Science Translational Medicine, pointed out last week that “you are literally going to have cases where someone gets the vaccine and drops dead the next day (just as they would have if they didn’t get the vaccine). It could prove difficult to convince that person’s friends and family of that lack of connection, though. Post hoc [association] . . . is one of the most powerful fallacies of human logic.”

The rollout still calls for extreme vigilance. Amid the expected quota of deaths and disease, there may be genuine cases of rare adverse events to Covid-19 vaccines that the trials have not been large enough to detect. The challenge will be to distinguish the signal from the noise.

Natalie’s family fought hard to stop their loss being wrongly paraded as a signal that vaccines cause harm. Three months after her death, her 18 year-old sister Abigail announced she would have the same immunisation. “I know Natalie died of a tumour and not the vaccine,” Ms Morton said. The HPV jab is so effective that the World Health Organization now believes it can help to eliminate cervical cancer by 2030.

That, after all is what vaccines are designed to do: protect us from death and disease, not cause them.

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