How strong is our defense against Covid-19?

 You may be wondering about your chances of getting infected or, worse, being hospitalized or dying if you get sick now that most US cities and states have dropped masking requirements and other precautions against Covid-19.


Researchers have been investigating this question, and in general, they've discovered that for people who are considered up to date on their Covid-19 vaccines – that is, they get a booster when it's recommended – protection against illness declines over three or four months after your last dose, but protection against hospitalization and death remains high.

This is why: Antibodies, the immune system's front-line defenders, gradually decline after an infection or vaccination. It's normal for them to fade away after a few months. However, it leaves your body vulnerable to another viral invasion.

The good news is that, while antibodies are essential for immune defense, they are not the end of the story. Other cells, such as B and T cells, are imprinted with the memory of the virus or vaccine, allowing them to create a new antibody army if they come into contact with the pathogen again.

It takes time to build an army, so you may experience some symptoms while your body prepares to fight. In the end, your immune system should come to your aid and assist you in recovering quickly.

This is how it is supposed to work in general. However, this process does not always go as planned for everyone. Older adults and those with weakened immune systems may require additional assistance to avoid the worst consequences of a Covid-19 infection.

After-infection defense

This is broken down in data presented this week to the US Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.

Here's how protection fared in real-world situations against an infection with the Omicron coronavirus variant that causes symptoms. If you have:

  • Two doses of the Johnson & Johnson vaccine are 30% effective between two and four months after injections.
  • Your vaccines are 55 percent effective between months 2 and 4 if you take one dose of Johnson & Johnson and one dose of an mRNA shot from Pfizer/BioNTech or Moderna.
  • Your vaccines are 63 percent effective between months 2 and 4 after three doses of an mRNA shot.
According to data from the UK's Health Security Agency, boosters provide almost no protection against Omicron infection after five months.

Protection against hospitalization in the event of a weakened immune system

When it comes to emergency care or hospitalization, the level of protection provided by vaccines is entirely dependent on your immune function.
Sara Tartof, an epidemiologist with Kaiser Permanente in Southern California, has been researching how well a third dose of the Pfizer mRNA vaccine keeps adults in her health system out of the hospital.
The vaccine's effectiveness against hospitalization was 85 percent up to three months after the third dose, but it dropped to 55 percent after three months. However, upon closer inspection, she discovered that these findings were largely influenced by immune status.
"We saw no waning except in the immunocompromised," Tartof said. "Vaccine effectiveness in immunocompromised individuals begins low and gradually declines."

However, for people with normal immune function, vaccine effectiveness against hospitalization remained high after three months (around 86 percent).

Her preliminary findings have been published in The Lancet Repiratory Medicine. Tartof says she'll be updating them soon with results broken down by immune status.
When it comes to the risk of being hospitalized with an infection caused by the Omicron variant, researchers have discovered that for adults 50 and older whose immune systems are functioning normally, protection starts high and remains high – around 84 percent – for up to six months after a booster dose.
Adults 50 and older with compromised immune systems, such as those who have had solid organ transplants or are undergoing cancer treatment, benefit from a booster vaccine initially but declines rapidly.
According to new CDC data, an immunocompromised adult can expect 81 percent protection from hospitalization if they get an infection caused by the Omicron variant up to two months after a booster dose of an mRNA vaccine, but that drops to about 49 percent after four months. One of the reasons this group has been prioritized for additional boosters is because of this.

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