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What We Know About Protection From Vaccines and Infections


  • The BA.5 subvariant of the omicron coronavirus accounts for the majority of COVID-19 cases in the U.S.
  • Recent research has found people who are fully vaccinated and had a previous COVID-19 case had the most robust antibody response.
  • New CDC research on people over age 50 also found that having a 2nd COVID-19 booster does help decrease the risk of infection.

COVID cases are increasing across the United States due to the immune-evasive and highly-transmissible BA.5 variant.

BA.5, which accounts for 65% of infections in the U.S., has mutations on the spike protein — the part of the virus that allows for cell entry — that have helped it spread quickly and partially evade antibodies generated from previous infections or vaccinations.

Recent evidence suggests that the type of variant you were previously infected with can influence your risk of reinfection.

People who previously had Omicron appear to be much more protected against new infections with Omicron subvariants than those infected with past variants like Delta. But even a recent Omicron infection won’t guarantee that you won’t get COVID-19 again sometime soon.

“BA.5 is different enough from some of the other Omicron strains that people have been reinfected fairly quickly after their prior infection,” Dr. Ted Cohen, an infectious disease epidemiologist at the Yale School of Public Health, told Healthline.

Reinfections are possible, even within weeks after a prior infection, but it’s unclear how common reinfections are.

A recent preprint of a study from Qatar found that the strength of immunity from a prior infection largely depends on which variant you were infected with. The study has yet to be peer-reviewed.

People who were infected with a variant that preceded Omicron — such as Delta or Alpha — were estimated to be about 15% protected from a symptomatic BA.5 reinfection. Individuals who developed an Omicron case — which was first detected in the United States in December 2021 — were estimated to be 76% protected against a symptomatic BA.5 reinfection.

“If people have had previous infections with Omicron lineage strains, they can be reinfected, but it’s quite plausible that they have more of the protection than those who had been infected before that,” Cohen said.

Though people who recently had an Omicron case appear to have greater protection, it’s unknown how durable that protection is, says Dr. Julie Parsonnet, an epidemiologist and professor of infectious diseases at Stanford University School of Medicine.

Prior evidence has shown that immunity against symptomatic infections wane with time. In general, the longer out from a past infection, you are, the less robust your immune response will be.

“Even quite recent infection with Omicron BA.1/BA.2 doesn’t provide complete protection against BA.4/BA.5. As the summer wears on, expect any protection to wane,” Parsonnet said.

Though BA.5 can evade antibodies — the initial immune response that protects us from infection — prior infection and vaccination provide strong protection against severe outcomes, according to Cohen.

Previous studies have looked at how vaccines and previous infections can protect against Omicron strains, although the research was done before the rise of BA. 5.

A study published in The New England Journal of Medicine indicated that three doses of the vaccine provided better protection than two doses. Data from a study of people over age 50 from the CDC similarly found that each additional dose boosts protection against infection.

“Booster vaccinations increase antibodies quite a bit, which helps to overcome some of the virus’ immune evasion,” Dr. Anne Liu, an infectious disease doctor, said.

The most severe infections continue to be in unvaccinated people, according to Cohen.

“It seems that the severity of disease is probably significantly less, so there is benefit in terms of prior infections and vaccination for severity of outcomes,” Cohen said.

Currently, daily cases of reported COVID-19 are averaging around 126,000, according to the CDC.

Sewage surveillance, which monitors the levels of the coronavirus in wastewater, has revealed that the current surge is likely much greater than what is being captured with testing.

“That’s an enormous amount of virus going around,” Parsonnet said.

Evidence has suggested that B.A. 5’s immune-evasive properties are raising the infection rate, but at the same time, most people are no longer adhering to the precautions previously used to mitigate the spread of COVID-19.

“The number of people infected by a single infected person also may increase because there are fewer precautions being taken now among the general population,’ Lui said.

Hospitalizations have increased nationwide by about 10% for the week ending July 10 compared to the previous week. But according to Parsonnet, the hospitalization rate can be difficult to pin down because many people may be admitted for other health issues but may simultaneously carry the virus, so they are listed as COVID infections.

The most important marker to track is the death rate, and at this time, deaths do not appear to be rising.

“Data continue to show that deaths among vaccinated are still lower than among unvaccinated, meaning that the vaccines are still doing what they are meant to do: save our lives,” Parsonnet said.

As BA.5 spreads rapidly across the country, many people are increasingly concerned about being reinfected. Recent evidence suggests that which variant you were previously infected with influences your risk of reinfection — people infected with Omicron appear to be more protected than those infected with an earlier variant like Delta or Alpha.

To get the most robust protection against coronavirus, experts recommend being fully up to date on COVID-19 vaccines no matter your previous COVID-19 history.



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