Watch a recording of the Wednesday, July 28 community update in which Roby Bhattacharyya and Deb Hung discuss the latest science around the COVID-19 Delta variant, and read Roby's answers to some of Broadies' questions asked during the update.
Broad-wide community update on COVID-19
Roby Bhattacharyya and Deb Hung shared what infectious disease experts know (and still don’t know) about the Delta variant of COVID-19 and what it means for public health.
Watch a recording:
COVID-19 Q&A with Roby
If the virus continues to mutate and we don't have a sufficient vaccination rate, could future mutations be vaccine-resistant?
It's very unlikely that vaccinated, immune-competent people will be at as much risk as they were before vaccines. Vaccination induces a polyclonal antibody response and T-cell immunity that will be hard for viruses to fully evade without the spike proteins losing the functions that make SARS-CoV-2 an effective virus.
From the perspective of unknown, long-term health effects of infection, should vaccinated people be worried about getting infected with COVID-19 even if they’re not hospitalized?
It's difficult to say at this point. Repeat exposures to other coronaviruses aren't so bad, but this is a new virus.
What is the timeline for pediatric emergency approval for the three available vaccines? And what age groups do you expect to be authorized?
Pfizer is planning to submit for approval to vaccinate children 5-11 years old by September, 2-5 years old shortly after, and 0.5-2 years old later this fall. However, FDA approval remains unknown. When cases were lower, they were suggesting they might want to wait an additional 2-4 months. It is possible they might reconsider that now.
How are “milder” symptoms defined? Are they very mild cold-like symptoms, or just not hospitalized but very sick at home?
"Mild" encompasses a whole range of symptoms, from asymptomatic to sick at home.
How do we know that the decrease in the percentage of cases leading to death is mainly due to the vaccine, instead of the currently more widespread Delta being perhaps less death-causing?
Based on what we've seen in places like India and Africa, and what we're seeing in our own hospitals, it seems like the Delta variant is more severe, not less, in unvaccinated individuals. The Delta variant in the UK looks to cause just as or more severe disease than the Alpha variant in unvaccinated people. Canada apparently has similar data now, per CDC (not publicly released yet). Alpha, in turn, was more contagious and caused more severe illness than the wild-type virus. This plot summarizes it most clearly for me. There is no doubt that vaccines are responsible for the disconnect between cases and deaths in the Delta surge in highly vaccinated countries.
How long does the protection from the vaccine last?
Still unknown, but protection from severe disease (hospitalization or death) appears to still be less than 95 percent at least eight months out. There is some reduction in apparent efficacy against milder cases, but that is very hard to tease apart from the different variants that are circulating now compared to when the trials were done (in other words, it may not be waning vaccination, it may be more evasive variants). The age-dependence of vaccine rollouts also complicates interpretation: If waning is seen, it’s not clear that the kinetics will be the same for younger people who were vaccinated later.
Since the efficacy of the current vaccines is likely to drop against new variants, is herd immunity still a thing that the U.S. should aim for?
It's important that we vaccinate as fast as we can. At some point, everyone in the world — to a first approximation — is likely to be exposed or vaccinated. Once we have all some degree of exposure, the pandemic may become more manageable. Immunity will get us most of the way there.
In Cambridge, of 83 confirmed or probable cases, 42 percent were vaccine "breakthrough" cases, meaning they were fully vaccinated but still got infected. 42 percent seems high! Should we worry about this?
The data suggests that Delta spreads more by transmission through unvaccinated individuals than by "evasion" of vaccines. Remember, as a higher fraction of people are vaccinated, and especially as those vaccinated people change their risk behavior, the expected percentages change — in MA, 84 percent of adults have had at least one vaccine dose; Middlesex County is more vaccinated than average for the state. (At the extreme, once everyone is vaccinated, 100 percent of cases will occur in vaccinated people.) And severe cases in the vaccinated are uncommon. But we are still learning about the risk of vaccinated people spreading Delta, so I think it’s fair to consider your risk of spreading to others when case counts are high, even if you’re vaccinated.
Are the breakthrough infections occurring among sufficiently vaccinated populations? How do we know if one active COVID-19 case in entirely vaccinated groups can cause infections to occur?
No vaccine is 100 percent perfect. We expect that as more contagious variants crop up and more people get infected, breakthrough cases will go up. However, vaccines are extremely effective against disease. The data suggest that vaccinated individuals who are infected may transmit, but they are less likely to be infected, and even if infected they are probably less likely to transmit (this was clearly the case with prior variants; we’re still waiting on quantitative data with Delta). The risk is higher for vaccinated individuals transmitting to unvaccinated individuals — not to other vaccinated individuals.
Roby Bhattacharyya (he/him)
Infectious Disease and Microbiome Program
MGH Division of Infectious Disease
Deb Hung (she/her)
Core Institute Member Co-director, Infectious Disease Program
Infectious disease physician at BWH and MGH
Jesse Souweine (she/her)
Chief Operating Officer