Fortunately, vaccines are forming a bulwark against severe disease, hospitalization and death. But with the specter of delta and the potential for new variants to emerge, is it time for booster shots — or even a new COVID vaccine?
For now, public health experts say the far bigger emergency is getting first and second doses into people who haven’t had a single shot. Most people don’t need boosters to prevent severe illness, and it’s not clear when or if they will. But companies are already looking into updating their vaccines for coronavirus mutations, and there is a good chance that third shots are coming soon for some people. Already, the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) have greenlighted booster shots for immunocompromised individuals.
“I think we’re looking at an inevitable move toward boosters, at least in higher-risk people like those of advanced age and obviously the immunocompromised,” said Dr. Eric Topol, a professor of molecular medicine at The Scripps Research Institute in California.
Vaccine developers are working on the question of whether future COVID-19 shots will need to be tweaked for the delta variant, or other new variants. For now though, initial evidence hints that boosters of the original vaccine should add protection against delta.
Vaccine efficacy against delta
While all the COVID-19 vaccines in the U.S. are doing a fabulous job of preventing severe disease and death, it’s clear that breakthrough infections are more common with this variant. Data on efficacy is still emerging, and efficacy is a moving target depending on a lot of factors. It’s hard to make apples-to-apples comparisons between countries or hospital systems, said Jordi Ochando, an immunologist and cancer biologist at the Icahn School of Medicine at Mount Sinai. Different countries have different levels of vaccination, have used different vaccine mixes with different dose scheduling, and have different populations with different age stratification, comorbidities and levels of previous infection.
Still, synthesizing data from different countries suggests the mRNA vaccines by Pfizer-BioNTech and Moderna are probably up to 60% or as low as 50% protective against infection with delta, Topol wrote on Twitter. That’s right on the border of efficacy at which the Food and Drug Administration would approve a new COVID-19 vaccine. The J&J vaccine is probably less protective against symptomatic illness than a two-dose mRNA vaccine, based on studies finding that it elicits lower levels of neutralizing antibodies (which block the virus from entering cells).
Data is now emerging that the J&J vaccine likely prevents severe disease from delta as well. Though people with symptomatic breakthrough infections can spread the delta variant, the vaccines do still seem to reduce the likelihood of transmission by making any infection that does occur shorter. A study conducted in Singapore found that viral load started at similar levels in vaccinated and unvaccinated individuals who were infected with delta, but it dropped much faster in vaccinated individuals, beginning a steeper decline around day 5 or 6 of illness. This could mean that vaccination shortens the infectious period. However, more confirmation is necessary to show whether the Singapore results will hold up. The discovery that vaccinated people can have viable virus in their noses if infected is what made the CDC reverse its recommendation that vaccinated people did not need to wear masks.