Covid-19 vaccines may cut transmission as well as symptoms

Once again, the Covid-19 health message is getting muddled. Even as officials and scientists urge the public to get vaccinated, they warn that after vaccination, we'll still have to go on isolating and wearing masks.

It's a mistake to oversimplify this way. We should be talking about using the vaccines to end the pandemic - not filling people with dread that they will be stuck with isolation and masks forever. The evidence is compelling that a strong, rapid vaccination campaign could render SARS-CoV-2 less of a threat than seasonal flu through building herd immunity.

Without herd immunity as a shared goal, some might skip the vaccine, influenced by scare stories about side effects and rare allergic reactions, especially if they are young and face only a small chance of dying from the virus.

It's simple enough to tell people that if we all work hard to avoid getting or spreading the disease during the vaccination campaign, and everybody steps up to get the shots, aspects of normal life could resume this year. And even before we reach herd immunity, people who live alone and are vaccinated might be able to visit other vaccinated people without undue fear of disease, guilt or social stigma. There is some encouraging data on herd immunity from the clinical trials of two leading vaccines, says infectious disease doctor Monica Gandhi of the University of California, San Francisco. While the three leading vaccines have proven extremely effective at preventing symptomatic illness, two showed some hints that they limited transmission of the virus as well.

In the trial for the Moderna vaccine, researchers tested all the participants for SARS-CoV-2 when they returned to get a second dose and found that the first dose alone was about 60 per cent effective at stopping so-called asymptomatic cases.

The trial for the vaccine made by Astra Zeneca included some weekly swabbing of participants who reported no symptoms, and concluded about 60 per cent effectiveness at stopping so-called asymptomatic cases.

Gandhi says she's not surprised - there's a biological reason to think vaccines will cut transmission rates. The immune response would presumably help the body fend off or quickly clear infection whether with or without symptoms.

Art Krieg, a doctor specializing in autoimmune disease and biotech founder, agrees. "Once people are getting vaccinated, it's almost inconceivable that this is not going to slow transmission," he says.

Some encouraging news also comes from research newly published in the journal Nature suggesting that protective immunity likely lasts many months, if not years, in those who have been infected. The same might apply to the vaccinated.

Herd immunity won't eradicate the disease, but will significantly slow it down. Earlier estimates have suggested that will kick in when about 70 per cent of the population has been infected or vaccinated, but that percentage may be higher or lower depending on how well the vaccines work against transmission and the rise of new variants that are more easily transmitted. The race against mutations should only serve as another motivating factor for a quick and persuasive vaccination campaign, since the odds of new variants go way down if people get vaccinated quickly. "The more people are infected by this virus, the faster new forms and new mutations are going to evolve," Krieg says.

UCSF's Gandhi says there's enough evidence to justify a hopeful message. "You have this ongoing debate from scientists about what to do after vaccination - do we mask and distance," she says. She worries that the current messages have led people to think they will have to avoid other people forever, "and that's not a way people can live." She's been vaccinated but is still taking precautions, such as wearing a mask at work. But the point of the vaccines, she says, is to end the isolation. (Bloomberg)

Faye Flam