While some who have had COVID-19 might not have an interest in getting vaccinated, a growing body of evidence and cautionary tales from other countries indicate that natural immunity won’t be the answer to beating the pandemic.

The most vulnerable people are those with no previous infection or vaccine, but new studies on vaccines and variants show that people who have had the virus but no vaccine are at more risk than those who are fully vaccinated.

“The notion that you’ve had the virus before and you’re protected: we’re seeing time and again now that that’s untrue,” said Dr. Vin Gupta, a physician and professor at the Institute for Health Metrics and Evaluation at the University of Washington. “We don’t have robust protection because of prior infection particularly because of transmission of these variants.”

The variant that originated in the United Kingdom, the B.1.1.7 variant, is the most common circulating in Washington state, and it has thus far been associated with more transmission and in some cases, more severe disease.

The U.K. variant is also associated with the highest number of breakthrough cases in the state so far, with 98 recorded cases of people who’ve been fully vaccinated testing positive with the variant.

People testing positive for the virus in recent months are, in essence, experiencing a different COVID-19 infection than those who were infected a year ago. Viruses mutate, and the more people don’t get vaccinated, the more opportunities the virus has to change its form, getting better in some mutations at evading antibody treatments or spreading faster.

Currently, the available vaccines in the United States are performing well against the variants, so much so that immune responses seen in fully vaccinated people are stronger than those who have had previous COVID-19 infection, experts say.

Gupta said he has been explaining this to his patients, especially those who have had COVID-19 and think they are immune. If the coronavirus hadn’t changed or evolved, their immunity might be stronger, but that’s not the reality.

“The antibodies you develop from infection from the original virus aren’t as useful,” Gupta said.

Vaccines are producing a more robust response at the biological level, he added.

Studies that measure antibodies in people who have had previous COVID infection have varied results, and scientists don’t yet know how long natural immunity lasts. Furthermore, some research has shown that antibody responses might be correlated with how severe a person’s disease was.

While some studies say a person who had the virus will have antibodies for months following infection, other studies show that variants can change that trajectory.

A May 2020 study from a placebo-controlled vaccine trial found that people who had had an older strain of COVID-19, before the South African variant was circulating, did not have reduced risk for getting infected again with the South African variant.

“The weakest form of protection looks like natural immunity,” Mike Famulare, a modeler with the Institute for Disease Modeling, said. “So the vaccines look as effective or better in terms of protecting you over a six-month time horizon of getting infected.”

On the opposite end of the spectrum, a person who has had COVID-19 and is fully vaccinated is likely the most protected a person can be against the virus.

“Having COVID plus vaccine is the most protected you can be,” Famulare said.

The Centers for Disease Control and Prevention changed its guidance for when people who tested positive for COVID-19 can be vaccinated in recent months. As soon as a patient with COVID-19 has resolved their symptoms and finished their isolation period, they can get vaccinated. The one exception to this rule is if a patient was treated in a hospital with monoclonal antibodies or convalescent plasma, the CDC recommends those patients wait 90 days before getting a vaccine.

Addressing ‘herd immunity’

To get to a level of immunity that will drive down the reproductive rate of the virus, health experts add together the number of people who have naturally acquired immunity to COVID-19 and the immunity gained by those who get vaccines.

In Washington, natural immunity is quite a bit lower than other parts of the country because residents here adhered to guidance so well. Lives were saved as a result, and now that means the state likely has more people vulnerable to the virus than other states with larger outbreaks or higher infection rates.

The Institute for Disease Modeling estimates that between 10% and 15% of Washington residents have natural immunity to COVID-19 from prior infection, according to Famulare.

If this is correct, combined with the 41% of Washington residents who have been fully vaccinated, a little more than 50% of the total state population has reached immunity status. This isn’t good enough for herd immunity levels, and health officials are now aiming for adequate vaccine coverage instead, with a goal of getting more than 70% of Washington residents the ages of 16 and over vaccinated in order to really keep the virus at bay.

The actual herd immunity threshold, Famulare said, is difficult to calculate due to the ever-changing nature of the virus, and even if we hit that magical threshold, COVID-19 won’t disappear immediately.

“What is herd immunity today may not be herd immunity tomorrow, so there will be a cat and mouse game we’ll play with this virus for many months,” he said.

What the future holds

COVID-19 won’t disappear when vaccination rates are higher, particularly in communities with low vaccination rates. There’s also the likelihood that we haven’t seen the end of the vaccine campaign either.

The idea of an annual vaccination or booster shot is definitely still on the table, Dr. John Lynch, infectious disease specialist at the University of Washington, said this month.

The danger remains for people and communities who do not get vaccinated, however, and in these nonimmune environments, variants will continue to mutate. So far, the vaccines have held up against variants, but if that is to change in the coming months or year, things could get a lot more challenging.

“Is it theoretically possible that a variant can get past vaccine immunity? I think it’s a theoretical concern,” Lynch said.

Gupta thinks it is possible that this coming fall and winter could be a “dangerous scenario” especially with seasonal changes, people gathering indoors and the lack of herd immunity. Hospitalizations could surge again.

“There’s a clear worry that that’s going to happen,” Gupta said.

The future Gupta is worried about is already happening on a smaller scale in some places with low vaccination rates today. Just ask health officials in northeastern Washington where an outbreak overwhelmed Republic’s critical access hospital after a superspreader event.

Roughly 30% of each county in northeastern Washington is fully vaccinated, leaving the majority of people vulnerable to the virus. And while local health officials don’t have a good indicator of how many people might have had the virus and now have some level of immunity, it likely isn’t so many people that there is more than 50% immunity in the region.

“In Eastern Washington we’re in this funny position where I think we’re going to deal with this longer than the West Side that has more people vaccinated, and our situation is reflected right now in our numbers,” Dr. Sam Artzis, health officer of the Northeast Tri County Health District, said earlier this month.

Ultimately, there is not going to be a hard stop to the pandemic where the virus just disappears, and Famulare thinks this coming year will likely bring a sort of adjustment to the virus in our lives instead of the pandemic suddenly being over. What that looks like depends a lot on vaccination rates.

“(Either) the way we live with the virus is different and better because everyone has gotten vaccinated or ugly because more people will die because they aren’t vaccinated,” he said.