IN A SEMI-VACCINATED WORLD, vaccinated people may get together with each other. For most everyone else, falling case numbers along with rising vaccination rates and new vaccines in the pipeline are raising hopes for making future plans —for next month, next summer, next year.
The many unknowns, meanwhile, create ongoing worries—that vaccinated people might still be able to spread the virus; that vaccine protection could last as little as three months; and that new variants may be able to evade current vaccines—although in each case, new research counters some of the worst possibilities.
One year into the pandemic, one theme prevails, notes local public health expert Lauren Greenberger: “I think there is still a lot that could change as more data becomes available—especially longitudinally.”
Those who have been vaccinated should be safe with each other, according to George Washington University health policy professor and former Baltimore health commissioner Leana Wen. “A couple who want to get together with another fully vaccinated couple are probably fine to do so, including to hug and see one another indoors, without masks. They should probably still avoid large gatherings.”
For the near future, “vaccines might never bring us to herd immunity but they can help end the pandemic,” writes Sarah Zhang in the Atlantic. Zhang notes that the definition of “herd immunity” is very precise: “a population reaches herd immunity when the average number of people infected by a single sick person falls below one. Patient zero might infect another person, but that second person can’t infect a third.”
Increasing the pace of vaccination to three million shots/day could make “total immunity” possible by May and “vaccine immunity” by July, according to the PHICOR public health research group—although both deadlines could change with the relaxation of social distancing and the spread of more contagious variants. “Total immunity” includes both the vaccinated and the previously infected, but it depends on estimates of those with infection-produced immunity; whereas “vaccine immunity” is based on real numbers and may be easier to predict, but it can change depending on the length of a vaccine’s effectiveness.
Instead of a herd-immunity goal, many experts focus on transforming Covid-19 from a much-feared cause of hospitalization and death into something closer to the seasonal flu via a combination of expanding vaccinations, improving treatments and maintaining social restrictions. The only caveat: Even mild Covid infection can cause debilitating, long-lasting symptoms.
Consorting with others, meanwhile, means observing the most conservative measures desired by the most worried person: Among those who have been vaccinated, although the risk of becoming infected is low, some worry about that small percentage of risk and ask others to wear masks and keep their distance.
A vaccinated visitor to an unvaccinated “pod” may be asked to stay somewhere safer than a hotel, like an Airbnb; to wear one or more masks when venturing into public spaces; and to take a Covid test following domestic air travel—even with the knowledge that those results will reflect, not post-flight infection status, but that of several days earlier, because that’s the rule of the pod.
Still unknown is what happens in the case of a sneeze from a vaccinated person who may have been recently exposed to infection. Injections into arm muscles create immunity in the body but may have no effect on viral particles that can reside in the nose and throat for five days or longer—and whether that amount of virus, or viral load, is sufficient to transmit the infection remains under study.
Using “viral load” as a proxy for infectiousness, the small number of people in one study who became infected two to four weeks after receiving the Pfizer vaccine had a “significant drop” in viral load compared to those who became infected during the first two weeks.
Also, the Pfizer vaccine showed 85% effectiveness in blocking not just symptomatic but also asymptomatic infection, according to new, unpublished research—providing “the first evidence that Pfizer’s vaccine might block transmission,” according to Nature.
Another troublesome data void is the length of immunity conferred by the vaccine. The most recent CDC recommendations stick to the three month limit: “vaccinated persons…are not required to quarantine if they…are within 3 months following receipt of the last dose in the series.”
On the other hand, studies have shown the persistence for at least eight months of immunity following Covid-19 infection—immunity conferred, not by antibodies, but by a different weapon of the immune system known as “memory B cells.”
Ever-mutating variants may become capable of evading immunity created by either vaccines or infection. Variants discovered recently in New York and California may increase the need for surveillance of travelers within the U.S., not to mention those going back and forth to Europe. Meanwhile, vaccine creators are working hard to find ways to adjust current products as well as to create boosters—to deal both with expiring immunity as well as mutations in variants.
For vaccinated travelers, Wen says, the risk is “already pretty low [and] can be reduced further by vaccinated visitors avoiding other social gatherings before travel.”
Reagan and Dulles airports expect to offer Covid-19 testing to travelers, both rapid tests and the more reliable PCR tests, within the next month, but offerings can differ by airline and may be more cumbersome and more expensive than visiting a free testing site after arrival.
The coronavirus continues to be devastating in sickness and lives lost, as well as in unemployment, poverty and many related ills. At the same time, the virus is creating better understanding of the interconnectedness of our world and our communities, and of how to take better care of each other—as well as of viruses themselves, which usually attack but can also contribute to our bodies’ health.
Eloquently exploring many unusual facets of viruses, Carl Zimmer addresses one basic question, whether they are dead or alive—quoting a 1930s New York Times article: “Enough is known about matter, organized and unorganized, to assure us that there may be things ‘twixt heaven and earth which are not so alive as an eel or so dead as a rock…”
Mary Carpenter has been closely following Covid-19 developments.