How strong is your immunity against Omicron?

For months, scientists, public health officials, politicians and the general public have debated whether prior SARS-CoV-2 infection — touted as “natural immunity” — offers protection against COVID-19 that is comparable to vaccines.

The answer to that debate is complicated, but studies show the best way to protect yourself against the Omicron variant of the coronavirus is to get vaccinated and then boosted. An infection on top of that, while not desirable, offers even more protection.

Recent evidence suggests that “natural” COVID-19 protection depends on many factors, including when the infection happened, the variant involved, whether someone has been boosted or not, and the overall strength of their immune system.

“The question about natural versus vaccination immunity is an important one,” Monica Gandhi, an infectious disease specialist and professor of medicine at the University of California, San Francisco, told Yahoo News. “The CDC showed that up to the Delta surge, no doubt, natural immunity is likely as protective or more protective even than your two-dose vaccines,” she added.

Gandhi was referring to a study published two weeks ago in the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report. It is the same study that GOP lawmakers pointed to this week when introducing the “Natural Immunity Transparency Act,” arguing that the CDC data “demonstrated natural immunity was 3-4 times as effective in preventing COVID-19 compared with vaccination.”

But this claim needs more context. The CDC study analyzed COVID-19 cases in California and New York in 2021, which together only account for about 18 percent of the U.S. population. The data was collected from May 30 to Nov. 20, 2021, a period before and during the Delta wave. The study showed that prior to Delta, which became predominant in late June and July 2021, case rates were lowest for people who were vaccinated and not previously infected with COVID-19. But by early October, when Delta was dominant, the picture changed. Case rates then were substantially lower among both unvaccinated and vaccinated people with previous infections, suggesting that natural immunity during this period was superior to vaccines.

However, it is important to note that the CDC research was conducted during a time when vaccine-induced immunity was waning for many people and before the emergence of the highly transmissible Omicron variant. Additionally, most U.S. adults were not yet eligible to receive booster shots, which are seen as offering the best protection against Omicron.

In general, studies conducted pre-Omicron do support the concept that infection-induced immunity and vaccine-induced immunity are pretty similar in terms of protection. However, Gandhi said there are many reasons vaccines are preferred. Notably, vaccines are free, safe and quick, while getting COVID-19 carries substantial risks, including long COVID, hospitalization and death. “It’s just safer,” Gandhi said.

She also said natural immunity can vary substantially from person to person, depending on many factors like age, the overall strength of the person’s immune system, how severe the COVID case was and the variant that infected them.

“What happens with natural infection is that if you have a mild infection, you may not mount the strong cellular immune response that you need to fight it in the future,” Gandhi said. On the other hand, vaccines were subject to rigorous trials and found to elicit a high immune response. Most experts agree that a vaccine is a more quantifiable, predictable and reliable way to protect the population.

Another downside to relying on natural immunity is that Omicron has replaced Delta as the dominant variant, and Omicron is both more transmissible and more capable of evading immune protection triggered by both vaccines and previous infections.

Shane Crotty, a virologist and professor at La Jolla Institute for Immunology, told Yahoo News that the Omicron variant changed everything. “Omicron is looking so different from the other variants that just infection alone might not be giving you great antibodies against the other variants because it looks so different,” he said. It is still unclear how much immunity one can expect to come out of an Omicron infection, including how long that protection lasts and whether it will apply to future variants.

Based on the epidemiological data available, Crotty said, those who are likely to be the most protected against both infection and hospitalization at the moment are people who have had a breakthrough infection. This means, individuals who have had an infection and then a vaccine, or vice versa.

“Data by tons of labs shows that those people make really broad neutralizing antibodies,” the professor said. “Their antibodies recognize every possible variant and even distant viral species, but they also make really high levels of those antibodies,” he added.

People in this category — both infection and vaccination — have what has become to be known as “hybrid immunity” or “super immunity.” According to a CDC study, those who get fully vaccinated after recovering from COVID-19 have twice the protection of those who do not get vaccinated after their recovery.

Experts warn, however, this doesn’t mean people should purposefully try to infect themselves with the coronavirus to achieve greater protection against COVID-19, since there are serious health risks involved.

People who are boosted also have an especially high level of protection against Omicron. “It’s pretty amazing three doses of the same vaccine, which is just against the ancestral strain. Your immune system is so clever. It’s seeing that old version of the spike protein basically, and the first two times it sees it, it makes neutralizing antibodies against the ancestral strain and a couple of variants, but not Omicron, but just seeing that same vaccine the third time, and now you make neutralizing antibodies against Omicron,” Crotty explained.

Underscoring the value of a third dose, recent studies by the CDC have shown a booster dose of the COVID-19 vaccine significantly reduces a person’s chance of hospitalization from the Omicron variant. One of the CDC reports, which looked at 259 hospitals and 383 emergency departments from late August through early January, found that a third dose of either the Pfizer or Moderna vaccine was 90 percent effective at preventing hospitalization and 82 percent effective at preventing emergency department and urgent care visits.

However, despite the evidence supporting the efficacy of a third dose, many Americans have been hesitant to receive their booster shots. Gandhi says this is unfortunate because boosters could be the ticket back to normal, and those who are unboosted or unvaccinated are more vulnerable to Omicron and future variants that could emerge. “What we need to get through this time is immunity ... so even if you’ve been actually infected, I really would recommend at least one dose of a vaccine,” Gandhi said.