Vaccines can get us to herd immunity, despite the variants

AHarvard immunologist said current vaccines appear to be effective enough to end the pandemic, despite growing concerns that more infectious COVID-19 variants would severely blunt the effectiveness of the preventative treatments and set the nation back in its fight against the disease.

Galit Alter, professor of medicine at Harvard Medical School and the Ragon Institute of MGH, MIT, and Harvard, said the fast-spreading U.K. variant seems able to evade some vaccine protection, and the South African variant appears able to skirt even more. Despite that, she said, none have completely escaped the body’s post-vaccination immune responses.

That’s because, Alter said, though much attention has focused on how antibodies boosted after vaccination target their attack on the virus’ spike protein, the immune system has an array of other defenses that vaccination also mobilizes, including antibodies that attack other parts of the virus, and, importantly, T-cells that attack the infected cells the virus hijacks in order to replicate.

“What we’re seeing is that these variants don’t seem to affect T-cell immunity all that much and they [the T-cells] seem to be as effective in recognizing these variants as they do the original virus,” Alter said. “What that means is that we actually have very important backup mechanisms built into our vaccines that will continue to provide protection against these newly emerging variants.”

Alter, speaking during a noontime briefing Wednesday by the Massachusetts Consortium on Pathogen Readiness (MassCPR), said that even if our most effective vaccines’ effectiveness falls to 70 percent from 95 percent, the world still has a path to achieving the herd immunity that can end the pandemic.

“What we see is that immunity conferred by the vaccine can essentially completely limit the breakout of any infections in the population,” Alter said. “These data give us hope that even with the vaccines that do not confer 95 percent protection against these emerging variants, the light at the end of the tunnel is approaching.”

That doesn’t mean the road ahead will be easy, Alter said. She acknowledged that the lower level of effectiveness against the variants means that more people will have to be vaccinated to achieve the same population-wide protective effects. Earlier estimates based on highly effective vaccines held that 50 percent to 60 percent of the population would have to be vaccinated in order to create herd effects. At 70 percent effectiveness, she said, the threshold will rise to roughly 75 percent, significantly higher, but nonetheless still achievable.

Short of that hopeful scenario, Alter said, lies another that is nonetheless preferable to the continuation of the current wave of widespread illness and death. Because the vaccines greatly reduce severe disease and death, a vaccination campaign that removes the most severe cases from the pandemic would mean that those that remained would be mild and asymptomatic cases, something similar to those caused by its close viral cousin: the common cold. In that case, Alter said, though the virus wouldn’t be eliminated, its effect would be blunted enough that the pandemic would also effectively end.

The online event, “Demystifying SARS-CoV-2 Variants,” was sponsored by MassCPR and hosted by HMS Dean George Daley. Daley said as we approach the mid-March anniversary of the World Health Organization declaring the coronavirus a global pandemic, the death toll from the virus has reached heights almost unimagined a year ago. Globally, there have been more than 113 million cases and 2.5 million deaths. In the U.S. alone, there have been more than 28 million cases and 500,000 deaths.

“The toll in lives has been extraordinary and the economic loss, also staggering,” Daley said. “While we in the medical community are guardedly hopeful and optimistic that the vaccines promise the end of the current pandemic, there is cause for concern that with the appearance of viral variants across the globe, we might be facing a decidedly novel stage of the contagion: COVID 2.0.”

Daley pointed out that while mutation is expected and most are harmless, the virus’ global spread gives it many more chances to hit on one that makes it more infectious or deadly. Jeremy Luban, a MassCPR member and professor at the University of Massachusetts Medical School, said that variants will continue to emerge and some, such as the P.1 version detected in Brazil, have caused alarm among scientists. In Manaus, Brazil, a large outbreak early in the pandemic caused scientists to conclude that nearly 70 percent of the population had been exposed and, after a lot of illness and death, the population had reached herd immunity. When the P.1 strain arrived in December, a second surge tore through the city, causing hospitalizations to rocket and raising concern the variant may be able to escape the immune response caused by prior infection.

Other participants discussed the potential for variants to weaken not just the effectiveness of vaccines, but also that of treatments developed to help those already sick. Monoclonal antibodies, which mirror humans’ natural antibodies and also target the virus’ spike protein, are potentially at risk, according to Jonathan Abraham, assistant professor of microbiology. He said that antibodies that attack different parts of the spike can be developed and strategies to attack other proteins important to the virus can also be targeted. Remdesivir, for example, attacks enzymes that play key roles in viral replication. Enzymes are attractive targets, Abraham said, because they mutate less frequently than other proteins in the virus and so could potentially provide lasting protection against different variants.


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