Questions About Waning Immunity, Answered

By Amichai Perlman, PhD, PharmD
Medically reviewed checkmarkMedically reviewed
January 2, 2022

In recent weeks, the CDC has expanded eligibility and updated the recommendations for COVID-19 vaccine boosters. The CDC now recommends that everyone aged 18 and older should get a booster shot, 6 months after completing the primary mRNA COVID-19 vaccination series. These recommendations have become especially pertinent with the renewed and rapid rise in the number of COVID-19 cases across the country.

What does waning immunity look like in the Covid-19 vaccines?

While initially there was some controversy regarding the need of boosters, it has now become very clear they are necessary to maintain immunity and reduce transmission in the face of the ongoing pandemic. 

The first doses of the vaccines, especially mRNA vaccines, create high levels of neutralizing antibodies, which dramatically reduce the risk of coronavirus infection. However studies have demonstrated that antibody levels significantly decline within 5-6 months, and that with this decline comes an increase in “breakthrough” infections. This phenomenon has been observed across age groups and vaccines, and happens with disease-induced immunity (AKA “natural immunity”) as well. There is also a decline in vaccine-protection from severe COVID-19, albeit a smaller one. 

Can I take an antibody test to see if I need a booster shot?

The immune response to COVID-19 is complex and includes both antibody as well as cell-mediated immunity. The exact contribution of the various components has yet to be determined. It has been shown that the levels of antibodies correlate with the risk of COVID-19 breakthrough infection. This data does not necessitate that each individual with low, or even unmeasurable antibodies, has lower immunity than each individual with higher levels of antibodies. Only that on average people with higher antibodies are better protected. Moreover the data is insufficient to establish definitive levels of antibodies which are protective, as there are additional variables that are correlated with the level of antibodies, time from vaccination, and risk of infection. In the future we may have additional information allowing us to infer immunity from antibodies, however current data is limited. So with the exception of possible “edge cases”, the primary measure for when one should get a booster is the time elapsed from the previous vaccination.

What role do the new variants play against my immunity?

As the coronavirus replicates inside human cells, small parts of its genetic code occasionally mutate. Most of these mutations are either meaningless or dysfunctional (result in a virus less fit to replicate and transmit). However, because the virus is so widespread and is replicating in many people around the world, it has many opportunities to develop a random mutation which is more contagious, causes more severe disease, or evades immunity conferred by current versions of the vaccine (as well as prior infection). 

When variants of the virus are identified as potentially more contagious, dangerous, or able to evade current vaccines or treatments, they are designated “variants of concern”. In retrospect, the concern regarding some variants turned out correct – such as the Delta variant which is considerably more contagious than previous variants. Other variants of concern had less of an impact. While there was concern regarding the efficacy of COVID-19 vaccines against Delta, it now appears the vaccines provide very effective protection against this variant as well, and the appearance of reduced efficacy was primarily due to vaccine waning.

It is too early to know what impact the new variant on the block – Omicron – will have. Scientists have identified many Omicron mutations as potentially impacting COVID transmissibility, severity, or vaccine evasion. However, actual data to date is very limited. Initial data suggests Omicron is more contagious than the Delta variant, that there is some reduction in vaccine effectiveness, and that people previously infected with coronavirus are more susceptible to reinfection with omicron. However, as our immune response involves developing antibodies and immune cells able to identify many parts of the coronavirus spike, it is most likely that vaccines retain at least partial efficacy in reducing the risk and severity of infection. In fact, recent news from Pfizer, on the levels of Omicron neutralizing antibodies in vaccinated individuals, suggest some protection from the vaccine, and that the booster likely confers significant protection. Among individuals who received a booster neutralizing antibody levels are similar to those seen against the original variant after two doses. Indeed, early data from Britain shows that compared to non-vaccinated people, individuals who received the Pfizer vaccine-booster were 76% less likely to catch the Omicron variant.

At what point, should I look at getting the booster shot?

The CDC recommends that if you were originally vaccinated with an mRNA vaccine (Pfizer-BioNTech for those 12 and older, or Moderna for those 18 and older), and have completed your primary vaccination series five months ago or more, you should get a booster. If you receive the Johnson & Johnson vaccine originally, you should get boosted when 2 months or more have elapsed from the receipt of the original dose. In most situations, the preferred booster for people originally vaccinated with Johnson & Johnson’s vaccine is an mRNA vaccine.

According to the CDC, there can be cases when boosters are warranted earlier, and for younger individuals as well, such as for some individuals who are immunocompromised – so contact your healthcare provider when in doubt.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Amichai Perlman, PhD, PharmD

Dr. Perlman is a clinical pharmacist and pharmacoepidemiologist, with over 10 years of experience advising patients and clinicians on medication use, personalization, and safety. He has extensively published peer-reviewed research addressing medication safety.