How a Cape Cod Covid outbreak upended what we know about vaccines – and could put us back in masks

Stunning findings from a 4 July cluster have upended the medical community’s assumptions, writes Helen Elfer

People bike down Commercial Street on May 25, 2020 in Provincetown, Massachusetts (Getty Images)

When Joe Biden delivered his first ever primetime address to the nation as president, he spoke of his high hopes that 4 July this year would "mark independence" from Covid-19 – as long as people got vaccinated.

Perhaps beachgoers in Provincetown, many of them comfortable in the knowledge that they’d done just that, remembered his words as they celebrated Independence Day over a relaxed weekend of barbecues, parties, packed bars and restaurants in the Massachusetts town on the tip of Cape Cod.

In fact, that weekend led to a Covid-19 outbreak that shocked health officials and upended medical assumptions, demonstrating as it did, that the Delta variant may be as transmissible by vaccinated as unvaccinated people.

As the Centers for Disease Control and Prevention (CDC) put it in a leaked data report revealed by the Washington Post: “The war has changed.”

Before Provincetown, it was considered extremely rare for a vaccinated person to become infected with Covid-19, let alone pass it on to others. But among the almost-900 confirmed Covid-19 cases linked to the cluster, 74 per cent were among vaccinated people.

The outbreak was “a pivotal discovery” about the Delta variant, said CDC chief Dr Rochelle Walensky in a statement about the new information, and it had led swiftly to the agency’s release of new guidance about wearing masks earlier in the week.

The fresh guidelines announced by the CDC urged vaccinated people in Covid-19 hotspots to resume wearing masks in indoor public places, regardless of their vaccination status. It also recommended indoor masks for all teachers, staff, students and visitors at schools nationwide.

It was in part a retraction of the CDC’s earlier guidance from May, which had said that vaccinated people no longer needed to wear masks in most settings, operating on the understanding that vaccines would largely prevent virus transmission.

But the latest CDC report, released on Friday, said that 127 vaccinated people infected with the Delta variant during the outbreak appeared to carry as much virus as 84 unvaccinated or partially vaccinated people who become infected.

Explaining the link between the Delta variant and so-called “breakthrough cases” where a person gets infected despite being fully vaccinated, Dr Walensky’s statement said: “High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with Delta can transmit the virus,” adding: “This finding is concerning.”

Underscoring just how much of a concern the Delta variant’s contagiousness could be, a leaked CDC slide presentation described the Delta variant as being as infectious “as chicken pox,” reported the Washington Post. Chicken pox affected as many as four million Americans a year before a vaccine was made available in the mid-1990s.

The Delta variant is more transmissible than the common cold, seasonal flu and smallpox according to the document, and each person infected with it can, on average, end up spreading the virus to eight or nine others.

“It is not a welcome piece of news that masking is going to be a part of people’s lives who have already been vaccinated,” Dr Walensky had said to reporters when she initially announced the CDC’s update. “This new guidance weighs heavily on me.”

But while the new CDC mask guidance was been read by many as a step backwards in America’s fight against the virus, not everyone interpreted the Provincetown outbreak the same way.

Alex Morse, the town’s manager, said that as he saw it: “The vaccines are working.”

“Day by day, things are improving,” Mr Morse told Yahoo News, adding that though it was unwelcome, the town’s speedy reimposition of a mask mandate had been crucial in improving infection rates.

Mr Morse also made a key point about the positive cases coming out of Provincetown: while 70 per cent of the cases were symptomatic, the symptoms were generally mild, there had been no surge in hospitalisations – and most importantly of all, none of the seven patients who were hospitalised with Covid-19 had died.

While any outbreak is “of course tragic,” said Washington, DC internist Dr Lucy McBride, this one “demonstrates the power of the Covid vaccines,” which have ensured that the overwhelming majority of Provincetown cases have been either mild or asymptomatic.

In contrast to commentators who have taken the new data on breakthrough cases to question the efficacy of vaccinations, the Provincetown cluster is in fact, she said, “a stark reminder of the critical importance of getting vaccinated”.

The CDC’s leaked document, despite its alarming comparisons to other infectious diseases, echoed her analysis. It said vaccinated people are safer, with the risk of severe disease or death decreasing 10-fold and the risk of contracting infection reducing as much as three times.

Vaccines may be less effective at preventing infection or transmission, but “prevent more than 90 per cent of severe disease” it said.