The Coronavirus Is Threatening a Comeback. Here’s How to Stop It. - The New York Times

Across the United States, and the world, the coronavirus seems to be loosening its stranglehold?

So far, the two vaccines authorized in the United States are spectacularly effective, and after a slow start, the vaccination rollout is picking up momentum.

Scientists say a contagious variant first discovered in Britain will become the dominant form of the virus in the United States by the end of March.

The road back to normalcy is potholed with unknowns: how well vaccines prevent further spread of the virus; whether emerging variants remain susceptible enough to the vaccines; and how quickly the world is immunized, so as to halt further evolution of the virus?

But if Americans let down their guard too soon — many states are already lifting restrictions — and if the variants spread in the United States as they have elsewhere, another spike in cases may well arrive in the coming weeks.

The United States has now recorded 500,000 deaths amid the pandemic, a terrible milestone.

The virus’s latest retreat in Rhode Island and most other states, experts said, results from a combination of factors: growing numbers of people with immunity to the virus, either from having been infected or from vaccination; changes in behavior in response to the surges of a few weeks ago; and a dash of seasonality — the effect of temperature and humidity on the survival of the virus.

The vaccines were first rolled out to residents of nursing homes and to the elderly, who are at highest risk of severe illness and death.

But young people drive the spread of the virus, and most of them have not yet been inoculated.

The B.1.1.7 variant is thought to be more contagious and more deadly, and it is expected to become the predominant form of the virus in the United States by late March.

A minority of experts were more sanguine, saying they expected powerful vaccines and an expanding rollout to stop the virus.

The vaccines have proved to be more effective than anyone could have hoped, so far preventing serious illness and death in nearly all recipients.

In a model completed before the variants surfaced, the scientists estimated that vaccinating just one million Americans a day would limit the magnitude of the fourth wave.

About 50 infections with those two variants have been identified in the United States, but that could change.

Because of the variants, scientists do not know how many people who were infected and had recovered are now vulnerable to reinfection.

South Africa and Brazil have reported reinfections with the new variants among people who had recovered from infections with the original version of the virus.

Yet the biggest unknown is human behavior, experts said.

Taking into account the counterbalancing rises in both vaccinations and variants, along with the high likelihood that people will stop taking precautions, a fourth wave is highly likely this spring, the majority of experts told The Times.

Despite the uncertainties, the experts predict that the last surge will subside in the United States sometime in the early summer.

If the Biden administration can keep its promise to immunize every American adult by the end of the summer, the variants should be no match for the vaccines.

Combine vaccination with natural immunity and the human tendency to head outdoors as weather warms, and “it may not be exactly herd immunity, but maybe it’s sufficient to prevent any large outbreaks,” said Youyang Gu, an independent data scientist, who created some of the most prescient models of the pandemic.

“Sometimes people lose vision of the fact that vaccines prevent hospitalization and death, which is really actually what most people care about,” said Stefan Baral, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

The virus will still be circulating, but the extent will depend in part on how well vaccines prevent not just illness and death, but also transmission.

Over the long term — say, a year from now, when all the adults and children in the United States who want a vaccine have received them — will this virus finally be behind us.

Many scientists said their greatest worry post-pandemic was that new variants may turn out to be significantly less susceptible to the vaccines

We might have slightly less good vaccines than we have at the moment,” said Andrew Read, an evolutionary microbiologist at Penn State University